Encapsulated Co-ZnO nanospheres as degradation tool for organic pollutants: Synthesis, morphology, adsorption and photo luminescent investigations

Zinc oxide (ZnO) nanostructures, both undoped and Co-doped, were synthesized through the solution combustion process. The diffraction patterns from powder XRD revealed that the materials were crystalline. The morphology of the spherically formed nanoparticles was visualized in SEM micrographs. FTIR spectra verified the existence of a defect-associated peak in Co-encapsulated ZnO (Zn_0.98Co_0.02O) NPs. Photoluminescence studies are undertaken. Malachite Green (MG) dye is used as a representative organic pollutant to study the adsorptive degradation of Co-doped ZnO nanomaterial. Moreover, the adsorption properties, including isotherm and kinetics, are investigated by analyzing the degradation of MG dye. Experimental parameters, such as the concentration of the MG dye, dosage and pH, were varied to ascertain favorable conditions for the degradation study. The results indicate that the MG dye is 70% degraded. After Co-doping, near-band edge emission in undoped ZnO changed into intense red defect emission and was directly correlated with changes in PL emission.

Adsorptive removal of Rhodamine B dye from aqueous solution by using graphene-based nickel nanocomposite

In this work, reduced graphene oxide-nickel (RGO–Ni) nanocomposite is synthesized. X-ray diffraction (XRD), scanning electron microscopy (SEM) and SEM–EDS (Energy Dispersive X-Ray Spectroscopy) are used to study the crystalline nature, morphology and elemental composition of the RGO–Ni nanocomposite, respectively. As synthesized RGO–Ni nanocomposite is used to develop selective adsorptive removal of Rhodamine B (RhB) dye from the aqueous solution. The experiments have been performed to investigate RhB uptake via RGO–Ni nanocomposites which include, contact time (60 min), initial dye concentration (50 mg/100 ml), adsorbent dosage (0.5 mg) and pH 8 of dye solution. The equilibrium concentration is determined by using different models namely, Freundlich, Langmuir and Tempkin. Langmuir isotherm has been fitted well. Langmuir and Tempkin equations are determined to have good agreement with the correlation coefficient data. The kinetic study concluded that RhB dye adsorption follows with the pseudo-second-order kinetic model. Further, adsorption mechanism of RGO–Ni is proposed which involves three steps. The synthesized adsorbent is compared with the other adsorbents in the literature and indicates that RGO–Ni nanocomposite used in this study shown better results for a particular adsorption capacity than polymeric, natural and synthetic bioadsorbents. The regeneration and reusability experiments suggest RGO–Ni nanocomposite can be used for many numbers of times for purification/adsorption.

Synthesis and characterization of Zinc oxide nanoparticles utilizing seed source of Ricinus communis and study of its antioxidant, antifungal and anticancer activity

ZnO nanoparticles have been synthesized using solution combustion technique and its antioxidant, antifungal, anticancer activity was studied. Ricinus communis plant seed extract used as fuel in synthesis by the solution combustion technique. Powder X-ray diffraction (PXRD) demonstrates the arrangement of a crystalline hexagonal stage (ICDD card number 89-1397) with space aggregate P63mc (186) and cell parameters a = b = 3.253, c = 5.213 Å. The normal crystallite measure is 20 nm which is ascertained by Debye - Scherer's formula. The Purity of the sample and metal to oxygen bond development was affirmed by utilizing Fourier transformation infrared (FTIR) spectroscopy and the particle size and shape was confirmed by HRTEM. Antifungal action of ZnO NPs was studied against Aspergillus and Penicillium by well dispersion strategy. The antifungal activity shows that ZnO NPs constitute as an effective fungicidal agent against both Aspergillus (4 ± 0.5 mm) and Penicillium (3 mm ± 0.4 mm) at 30 μg/mL fixation. ZnO nanoparticles were subjected to antioxidant activity. The objective of the study was to analyze the anticancer property of ZnO NPs on MDA-MB 231 cancer cells. To check the efficacy of the synthesized drug ZnO NPs MTT assay was performed, that determines % viability and/or cytotoxicity. IC₅₀ of ZnO NPs in case of MDA-MB-231 breast cancer was 7.103 μg/mL. Anticancer outcome demonstrates that ZnO NPs is active against in MDA-MB-231 cells.

Charge compensation assisted enhancement of photoluminescence in combustion derived Li+ co-doped cubic ZrO2:Eu3+ nanophosphors

Red light emitting cubic Zr_0.99Eu_0.01O₂:Li⁺ (0-9 mol%) nanoparticles are synthesized by a low temperature, self-propagating solution combustion method using oxalyl di-hydrazide (ODH) as fuel. In this study, we report systematic investigation of the effect of lithium ion (Li⁺) concentration on the structural properties and the photoluminescence of zirconia. With increasing lithium concentration, the crystallinity of the samples increases and the lattice strain decreases. The higher crystallinity is likely due to charge compensation achieved by replacing one Zr⁴⁺ ion by a Eu³⁺ and a Li⁺ ion. Scanning electron micrographs (SEM) reveal a mesoporous structure characteristic of combustion derived nanomaterials. Photoluminescence (PL) spectra show that the intensity of the red emission (606 nm) is highly dependent on Li⁺ ion concentration. Furthermore there is a promising enhancement in the associated lifetime. Upon Li⁺ doping, the PL intensity of the samples is found to increase by two fold compared to the undoped sample. Variation of PL intensity with Li⁺ concentration is attributed to the differences in probability of non-radiative recombination (relaxing). Intensity parameters (Ω₂, Ω) and radiative properties such as transition rates (A), branching ratios (β), stimulated emission cross-section (σ_e), gain bandwidth (σ_e × Δλ_eff) and optical gain (σ_e × τ) are calculated using the Judd-Ofelt theory. The calculated values suggest that in optimally co-doped samples, in addition to improved crystallinity and charge compensation, the lowering of Eu³⁺ site symmetry and the increase in the covalency of Eu-O bonding due to interstitial Li are responsible for the observed enhancement in PL intensity.

A single phase, red emissive Mg2SiO4:Sm3+ nanophosphor prepared via rapid propellant combustion route

Mg2SiO4:Sm3+ (1-11 mol%) nanoparticles were prepared by a rapid low temperature solution combustion route. The powder X-ray diffraction (PXRD) patterns exhibit orthorhombic structure with α-phase. The average crystallite size estimated using Scherer's method, W-H plot and strain-size plots were found to be in the range 25-50 nm and the same was confirmed by Transmission Electron Microscopy (TEM). Scanning electron microscopy (SEM) pictures show porous structure and crystallites were agglomerated. The effect of Sm3+ cations on luminescence of Mg2SiO4 was well studied. Interestingly the samples could be effectively excited with 315 nm and emitted light in the red region, which was suitable for the demands of high efficiency WLEDs. The emission spectra consists of four main peaks which can be assigned to the intra 4-f orbital transitions of Sm3+ ions 4G5/2→6H5/2 (576 nm), 4G5/2→6H7/2 (611 nm), 4G5/2→6H9/2 (656 nm) and 4G5/2→6H11/2 (713 nm). The optimal luminescence intensity was obtained for 5 mol% Sm3+ ions. The CIE (Commission International de I'Eclairage) chromaticity co-ordinates were calculated from emission spectra, the values (0.588, 0.386) were close to the NTSC (National Television Standard Committee) standard value of red emission. Coordinated color temperature (CCT) was found to be 1756 K. Therefore optimized Mg2SiO4:Sm3+ (5 mol%) phosphor was quite useful for solid state lighting.

Synthesis, characterization and photoluminescence properties of Bi³⁺ co-doped CaSiO₃:Eu³⁺ nanophosphor

Ceramic luminescent powders with the composition Ca(0.96-x)Eu0.04Bi(x)SiO3 (x=0.01-0.05) were prepared by solution combustion method. The nanopowders are characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) techniques. PXRD patterns of calcined (950°C for 3h) Ca(0.96-x)Eu0.04Bi(x)SiO3 powders exhibit monoclinic phase with mean crystallite sizes ranging from 28 to 48 nm. SEM micrographs show the products are foamy, agglomerated and fluffy in nature due to the large amount of gases liberated during combustion reaction. TEM micrograph shows the crystalline characteristics of the nanoparticles. Upon 280 nm excitation, the photoluminescence of the Ca(0.96-x)Eu0.04Bi(x)SiO3 particles show red emission at 611 nm corresponding to 5D0→7F2 transition. It is observed that PL intensity increases with Bi(3+) concentration. Our work demonstrates very interesting energy transfer from Bi(3+) to Eu(3+) in CaSiO3 host.

Synthesis, luminescence properties and EPR investigation of hydrothermally derived uniform ZnO hexagonal rods

One-dimensional (1D) zinc oxide (ZnO) hexagonal rods have been successfully synthesized by surfactant free hydrothermal process at different temperatures. It can be found that the reaction temperature play a crucial role in the formation of ZnO uniform hexagonal rods. The possible formation processes of 1-D ZnO hexagonal rods were investigated. The zinc hydroxide acts as the morphology-formative intermediate for the formation of ZnO nanorods. Upon excitation at 325 nm, the sample prepared at 180°C show several emission bands at 400 nm (∼3.10 eV), 420 nm (∼2.95 eV), 482 nm (∼2.57 eV) and 524 nm (∼2.36 eV) corresponding to different kind of defects. TL studies were carried out by pre-irradiating samples with γ-rays ranging from 1 to 7 kGy at room temperature. A well resolved glow peak at ∼354°C was recorded which can be ascribed to deep traps. Furthermore, the defects associated with surface states in ZnO nano-structures are characterized by electron paramagnetic resonance.

Zn2TiO4:Eu(3+) nanophosphor: self explosive route and its near UV excited photoluminescence properties for WLEDs

A simple and low-cost solution combustion method was used to prepare Eu(3+) (1-11mol%) doped Zn2TiO4 nanophosphors at 500°C using zinc nitrates as precursors and oxalyl di-hydrazide (ODH) as fuel. The final product was calcined at 1100°C for 3h and then characterized by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-visible absorption (UV-Vis). The PXRD patterns of the sample calcined at 1100°C show pure cubic phase. The crystallite size was estimated using Scherrer's method and found to be in the range 20-25nm and the same was confirmed by TEM studies. Effects of Eu(3+) (1-11mol%) cations on the luminescence properties of Zn2TiO4 nanoparticles were studied. The samples exhibit intense red emission upon 395nm near ultra violet (NUV) excitation. The characteristic emission peaks recorded at ∼578, 592, 613 and 654nm may be attributed to the 4f-4f intra shell transitions ((5)D0→(7)Fj=0,1,2,3) of Eu(3+) cations. The CIE chromaticity co-ordinates and CCT were calculated from emission spectra and the values (x, y) were very close to NTSC standard values for red emission and CCT was close to Plankian locus. Therefore, the present phosphor may be highly useful for display applications.

Role of flux on morphology and luminescence properties of Sm(3+) doped Y2SiO5 nanopowders for WLEDs

The study involves preparation of samarium doped Y2SiO5 (YSO) nano powders by solution combustion method using urea as a fuel for the first time. Effect of different fluxes on the crystallization behavior, morphology and photoluminescence (PL) properties of YSO:Sm(3+) (1-9 mol%) were investigated. The final product was characterized by Powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM) and UV-Vis spectroscopy. The average crystallite size estimated by Debye-Scherer's and Williamson-Hall plots were found to be in the range of 10-50 nm. Samples calcined at 1100°C show pure monoclinic X1 phase; whereas, samples calcined at 1200 and 1300°C show pure X2 phase of YSO. Photoluminescence (PL) studies of Sm(3+) (1-9 mol%) doped YSO for near ultra violet (NUV) excitation (407 nm) was studied in order to investigate the possibility of its use in white light emitting diode (WLED) applications. The emission spectra consists of intra 4f transitions of Sm(3+), such as (4)G5/2→(6)H5/2 (∼560 nm), (4)G5/2→(6)H7/2 (600-613 nm), (4)G5/2→(6)H9/2 (∼650 nm), (4)G5/2→(6)H11/2 (715 nm) and (4)G5/2→(6)H13/2 (763 nm) respectively. The emission intensity of the phosphor was found to be enhancing after addition of fluxes. Further, the emission at 600-613 nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for near ultra violet excitation.

GdAlO3:Eu(3+):Bi(3+) nanophosphor: synthesis and enhancement of red emission for WLEDs

GdAlO3, GdAlO3:Eu(3+) and GdAlO3:Eu(3+):Bi(3+) nanophosphors were synthesised by solution combustion technique. Pure orthorhombic phase was obtained from powder X-ray diffraction (PXRD) studies. Scanning electron microscopy (SEM) micrographs showed the porous, agglomerated and irregular shaped particles. The particle size obtained by transmission electron microscopy (TEM) measurement was in good agreement with the values obtained by Debye Scherrer's and W-H plots. The selected area electron diffraction (SAED) pattern show single crystalline nature of the sample. Photoluminescence (PL) measurements were carried out for GdAlO3:Eu(3+) and GdAlO3:Eu(3+):Bi(3+) phosphors excited at a wavelength of 274nm. The characteristic emission peaks of Eu(3+) ions were recorded at 590, 614, 655 and 695nm corresponding to (5)D0→(7)FJ (J=1, 2, 3, 4) transitions respectively. However, with addition of Bi(3+) ions in GdAlO3:Eu(3+), PL intensity drastically enhanced. Orange red color was tuned to deep red color with the addition of Bi(3+) ions in GdAlO3:Eu(3+) phosphor. Therefore, the phosphor was highly useful as red component in WLEDs. A single well resoled glow peak at 225°C was recorded in GdAlO3 and GdAlO3:Eu(3+). Further, with addition of Bi(3+) ions, an additional peak at 300°C was recorded. TL glow curves of different UV-exposed GdAlO3:Eu(3+):Bi(3+) show two TL peaks at 207 and 300°C respectively. The 207°C peak show simple glow peak structure and its intensity increases linearly up to 25min and after that it decrease.

Role of Cu2+ ions substitution in magnetic and conductivity behavior of nano-CoFe2O4

Cobalt copper ferrite nanopowders with composition Co1-xCuxFe2O4 (0.0≤x≤0.5) was synthesized by solution combustion method. The powder X-ray diffraction studies reveal the formation of single ferrite phase with particle size of ∼11-35 nm. Due to increase in electron density with in a material, X-ray density increase with increase of Cu2+ ions concentration. As Cu2+ ions concentration increases, saturation magnetization decreases from 38.5 to 26.7 emu g(-1). Further, the squareness ratio was found to be ∼0.31-0.46 which was well below the typical value 1, which indicates the existence of single domain isolated ferrimagnetic samples. The dielectric and electrical modulus was studied over a frequency range of 1 Hz to 1 MHz at room temperature using the complex impedance spectroscopy technique. Impedance plots showed only one semi-circle which corresponds to the contributions of grain boundaries. The lower values of dielectric loss at higher frequency region may be quite useful for high frequency applications such as microwave devices.

Luminescence studies and EPR investigation of solution combustion derived Eu doped ZnO

ZnO:Eu (0.1 mol%) nanopowders have been synthesized by auto ignition based low temperature solution combustion method. Powder X-ray diffraction (PXRD) patterns confirm the nanosized particles which exhibit hexagonal wurtzite structure. The crystallite size estimated from Scherrer's formula was found to be in the range 35-39 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal particles are agglomerated with quasi-hexagonal morphology. A blue shift of absorption edge with increase in band gap is observed for Eu doped ZnO samples. Upon 254 nm excitation, ZnO:Eu nanopowders show peaks in regions blue (420-484 nm), green (528 nm) and red (600 nm) which corresponds to both Eu2+ and Eu3+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits a broad resonance signal at g=4.195 which is attributed to Eu2+ ions. Further, EPR and thermoluminescence (TL) studies reveal presence of native defects in this phosphor. Using TL glow peaks the trap parameters have been evaluated and discussed.

Synthesis, characterization and spectroscopic investigation of Cr3+ doped wollastonite nanophosphor

This work explores the preparation of nanocrystalline Cr(3+) (1-5 mol%) doped CaSiO3 phosphors by solution combustion process and study of its photoluminescence (PL) behavior. The nanopowders are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red (FTIR) spectroscopy. PXRD results confirm monoclinic phase upon calcination at 950°C for 3h. SEM micrographs indicates that the powder is highly porous and agglomerated. The TEM images show the powder to consist of spherical shaped particles of size ∼30-60 nm. Upon 323 nm excitation, the emission profile of CaSiO3:Cr(3+) exhibits a narrow red emission peak at 641nm due to (2)E→(4)A2 transition and broad band at 722 nm due to (4)T2g→(4)A2g. It is observed that PL intensity increases with increase in Cr(3+) concentration and highest PL intensity is observed for 3 mol% doped sample. The PL intensity decreases with further increase in Cr(3+) doping. This decrease in PL intensity beyond 3 mol% is ascribed to concentration quenching. Racah parameters are calculated to describe the effects of electron-electron repulsion within the crystal lattice. The parameters show 21% reduction in the Racah parameter of free ion and the complex, indicating the moderate nephelauxetic effect in the lattice.

Gd(1.96-x)Y(x)Eu0.04O3 (x = 0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors: propellant combustion synthesis, structural and luminescence studies

Gd(1.96-x)Y(x)Eu0.04O3 (x = 0.0, 0.49, 0.98, 1.47, 1.96 mol%) nanophosphors were synthesized by propellant combustion method at low temperature (400°C). The powder X-ray diffraction patterns of as formed Gd1.96Eu0.04O3 showed monoclinic phase, however with the addition of yttria it transforms from monoclinic to pure cubic phase. The porous nature increases with increase of yttria content. The particle size was estimated from Scherrer's and W-H plots which was found to be in the range 30-40 nm. These results were in well agreement with transmission electron microscopy studies. The optical band gap energies estimated were found to be in the range 5.32-5.49 eV. PL emission was recorded under 305 nm excitation show an intense emission peak at 611 nm along with other emission peaks at 582, 641 nm. These emission peaks were attributed to the transition of (5)D0→(7)FJ (J = 0, 1, 2, 3) of Eu(3+) ions. It was observed that PL intensity increases with increase of Y content up to x = 0.98 and thereafter intensity decreases. CIE color co-ordinates indicates that at x = 1.47 an intense red bright color can be achieved, which could find a promising application in flat panel displays. The cubic and monoclinic phases show different thermoluminescence glow peak values measured under identical conditions. The response of the cubic phase to the applied dose showed good linearity, negligible fading, and simple glow curve structure than monoclinic phase indicating that suitability of this phosphor in dosimetric applications.

Synthesis and luminescence properties of Sm3+ doped CaTiO3 nanophosphor for application in white LED under NUV excitation

CaTiO3:Sm(3+) (1-11 mol%) nanophosphors were successfully synthesized by a low temperature solution combustion method [LCS]. The structural and morphological properties of the phosphors were studied by using Powder X-ray diffractometer (PXRD), Fourier transform infrared (FTIR), X-ray photo electron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). TEM studies indicate that the size of the phosphor is ∼20-35 nm. Photoluminescence (PL) properties of Sm(3+) (1-11 mol%) doped CaTiO3 for NUV excitation (407 nm) was studied in order to investigate the possibility of its use in White light emitting diode (WLED) applications. The emission spectra consists of intra 4f transitions of Sm(3+), such as (4)G5/2→(6)H5/2 (561 nm), (4)G5/2→(6)H7/2 (601-611 nm), (4)G5/2→(6)H9/2 (648 nm) and (4)G5/2→(6)H11/2 (703 nm) respectively. Further, the emission at 601-611 nm show strong orange-red emission and can be applied to the orange-red emission of phosphor for the application for near ultra violet (NUV) excitation. Thermoluminescence (TL) of the samples irradiated with gamma source in the dose range 100-500 Gy was recorded at a heating rate of 5°Cs(-1). Two well resolved glow peaks at 164°C and 214°C along with shouldered peak at 186°C were recorded. TL intensity increases up to 300 Gy and thereafter, it decreases with further increase of dose. The kinetic parameters namely activation energy (E), frequency factor (s) and order of kinetics were estimated and results were discussed in detail.

Effect of different fuels on structural, photo and thermo luminescence properties of solution combustion prepared Y(2)SiO(5) nanopowders

Y(2)SiO(5) nanopowders are prepared by solution combustion method using DFH, sugar and urea as fuels. The final product was well characterized by powder X-ray diffraction, Scanning Electron Microscopy and UV-Vis spectroscopy. The average crystallite size was estimated using Debye-Scherer's formula and Williamson-Hall plots and are found to be in the range 34-40nm for DFH, 45-50nm for urea and 35-42nm for sugar respectively. X1-X2 type YSO phase was obtained for all the samples calcined from 1200 to 1400°C. The optical energy band gaps (Eg) of the samples were estimated from Tauc relation and varies from 5.58 to 5.60eV. SEM micrographs of sugar and urea used Y(2)SiO(5) show agglomerated particles with porous morphology. However, for the sample prepared using DFH fuel observed to be almost spherical in shape. Thermoluminescence (TL) properties of γ-irradiated (1-5kGy) and UV irradiated (1-30min) Y(2)SiO(5) nanopowder at a heating rate of 2.5°Cs(-1) was studied. The samples prepared by using urea and sugar fuels show a broad TL glow peak at 189°C. However, DFH used Y(2)SiO(5) show a well resolved peak at 196°C with shouldered peak at 189°C. Among the fuels, DFH used Y(2)SiO(5) show simple glow peak structure which perhaps useful in radiation dosimetry. This may be due to fuel and particle size effect. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics are estimated by Chens glow peak shape method.

Study on low temperature solution combustion synthesized Sr(2)SiO(4):Dy(3+) nano phosphor for white LED

A series of Dy(3+) (1-5mol.%) activated Sr2SiO4 nanophosphors were prepared by low temperature solution combustion method using oxalyl dihydrazide (ODH) as a fuel. The obtained phosphor was well characterized by powder X-ray diffraction, scanning electron microscopy, and UV-visible spectroscopy. The average crystallite sizes were estimated by Debye-Scherrer formula and Williamson-Hall plots and found to be in the range 20-32nm. Energy band gap was found to be widened with increase of Dy(3+) ion dopant. Photoluminescence spectra consist of three main groups of peaks in 460-500nm (blue), 555-610nm (yellow) and 677nm (red) respectively. These peaks were assigned to transition of (4)F9/2→(6)H15/2,13/2,11/2. The critical distance between Dy(3+) ions and quenching site was found to be ∼16.71Ǻ. The chromaticity co-ordinates of all the prepared phosphors were located in white light; as a result Dy(3+) activated Sr2SiO4 is a promising single phased phosphor for white light emitting diodes. Thermoluminescence (TL) of Dy(3+) doped Sr2SiO4 nanophosphors were investigated using γ-irradiation in the dose range 1-6kGy at a warming rate of 2.5°Cs(-1). The phosphors show a well resolved single glow peak at ∼145°C. The kinetic parameters were estimated by different methods and the results discussed. The TL intensity increases linearly with γ-dose at room temperature. The effect of fading with storage time was found to be ∼66% which is highly useful in radiation dosimetry.

Synthesis, EPR and luminescent properties of YAlO3:Fe3+ (0.1-0.9mol%) nanopowders

A simple and inexpensive combustion method was used to prepare Fe(3+) doped YAlO3 perovskite within few minutes at low temperature (400±10°C). This might be useful in lowering the cost of the material. The final products were well characterized by various spectroscopic techniques such as PXRD, SEM, TEM, FTIR and UV-Visible. The average crystallite size was estimated from the broadening of the PXRD peaks and found to be in the range 45-90nm, the results were in good agreement with the W-H plots and TEM. The crystallites show dumbbell shape, agglomerated particles with different size. The TL glow curves of 1-5kGy γ-irradiated YAlO3:Fe(3+) (0.1mol%) nanopowder warmed at a heating rate of 3°Cs(-1) records a single glow peak at ∼260°C. The kinetic parameters namely activation energy (E), order of kinetics (b) and frequency factor (s) were determined at different gamma doses using the Chens glow peak shape method and the results were discussed in detail. The photoluminescence spectra for Fe(3+) (0.1-0.9mol%) doped YAlO3 records the lower energy band at 720nm ((4)T1 (4G)→(6)A1 (6S)) and the intermediate band located at 620nm ((4)T2 ((4)G)→(6)A1 (6S)) with the excitation of 378nm. The higher energy band located at 514nm was associated to (4)E+(4)A1 ((4)G)→(6)A1 (6S) transition. The resonance signals at g values 7.6, 4.97, 4.10, 2.94, 2.33 and 1.98 were observed in EPR spectra of Fe(3+) (0.1-0.9mol%) doped YAlO3 recorded at room temperature. The g values indicate that the iron ions were in trivalent state and distorted octahedral site symmetry was observed.

Low temperature synthesis of pure cubic ZrO2 nanopowder: structural and luminescence studies

Pure cubic zirconia (ZrO2) nanopowder is prepared for the first time by simple low temperature solution combustion method without calcination. The product is characterized by Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infra Red spectroscopy (FTIR) and Ultraviolet-Visible spectroscopy (UV-Vis). The PXRD showed the formation of pure stable cubic ZrO2 nanopowders with average crystallite size ranging from 6 to 12 nm. The lattice parameters were calculated from Rietveld refinement method. SEM micrograph shows fluffy, mesoporous, agglomerated particles with large number of voids. TEM micrograph shows honey comb like arrangement of particles with particle size ∼10 nm. The PL emission spectrum excited at 210 nm and 240 nm consists of intense bands centered at ∼365 and ∼390 nm. Both the samples show shoulder peak at ∼420 nm, along with four weak emission bands at ∼484, ∼528, ∼614 and ∼726 nm. TL studies were carried out pre-irradiating samples with γ-rays ranging from 1 to 5 KGy at room temperature. A well resolved glow peak at 377 °C is recorded which can be ascribed to deep traps. With increase in γ radiation there is linear increase in TL intensity which shows the possible use of ZrO2 as dosimetric material.

Low temperature synthesis, structural and dosimetric characterization of ZnAl2O4:Ce3+ nanophosphor

Dosimetric properties of γ-irradiated ZnAl2O4:Ce(3+) (1-9 mol%) nanophosphors were studied and reported for the first time. The phosphor prepared by solution combustion route was well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. PXRD patterns of calcined phosphor show pure cubic phase of ZnAl2O4:Ce(3+). Flake type morphology was observed from SEM studies. The particle size estimated by Scherrer's and Williamson Hall (W-H) plots and found to be in the range 11-17 nm. From photoluminescence (PL) studies two characteristic emission peaks at 363 and 480 nm were observed due to 5d-4f transitions of Ce(3+) ions. The thermoluminescence (TL) glow curves of ZnAl2O4:Ce(3+) (1-9 mol%) nanophosphor recorded two glow peaks 145 and 215 °C at a warming rate of 2.5 °C s(-1). The optimized TL intensity was observed for ∼5 mol% Ce(3+) concentration. The two TL glow peaks in the γ-irradiated (0.1-6 kGy) ZnAl2O4:Ce(3+) (5 mol%) nanophosphor indicates that two set of traps were activated within the temperature range 145 and 215 °C. The kinetic parameters (E,b,s) associated with the prominent glow peaks were estimated using Chen's glow peak shape method. The intensity of the TL glow peak (145 °C) increases linearly with increase of γ-dose upto 1 kGy above which it follows sub-linear behavior. Track interaction model (TIM) was used to explain the linearity/sub linearity/saturation behavior of TL intensity. The TL glow curves show simple glow peak structure, good reusability, low fading and wide range of linearity. Hence, the optimized ZnAl2O4:Ce(3+) (5 mol%) nanophosphor was quite useful for radiation dosimetry and display applications.

Synthesis, structural and luminescence studies of magnesium oxide nanopowder

Nanoparticles of magnesium oxide (MgO) have been prepared by low temperature solution combustion and hydrothermal method respectively. Powder X-ray diffraction (PXRD) patterns of MgO samples prepared by both the methods show cubic phase. The Scanning Electron Microscopy (SEM) studies reveal, the combustion derived product show highly porous, foamy and fluffy in nature than hydrothermally derived sample. The optical absorption studies of MgO show surface defects in the range 250-300 nm. The absorption peak at ∼290 nm might be due to F-centre. Photoluminescence (PL) studies were carried upon exciting at 290 nm. The sample prepared via combustion method show broad emission peak centred at ∼395 nm in the bluish-violet (3.14 eV) region. However, in hydrothermal prepared sample show the emission peaks at 395 and 475 nm. These emission peaks were due to surface defects present in the sample since nanoparticles exhibits large surface to volume ratio and quantum confinement effect.

Synthesis and photoluminescence properties of a novel Sr2CeO4:Dy3+ nanophosphor with enhanced brightness by Li+ co-doping

A series of Dy³⁺ (0.005–0.09 mol%) and Li⁺ (0.005–0.03 mol%) co-doped strontium cerate (Sr₂CeO₄) nanopowders are synthesized by low temperature solution combustion synthesis.

Investigation of structural and luminescence properties of Ho(3+) doped YAlO3 nanophosphors synthesized through solution combustion route

YAlO3:Ho(3+) (1-5mol%) nanophosphors have been prepared by solution combustion route using oxalyl dihydrazide (ODH) as a fuel. The final product was well characterized by powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis, etc. PXRD patterns confirm the formation of highly crystalline orthorhombic phase structure. SEM and TEM studies show the particles are dumbbell shape, highly agglomerated and nano-size (∼30nm). The direct energy band gap (Eg) values estimated from Tauc's relation were found to be in the range 5.76-5.99eV. Photoluminescence (PL) studies show green (540 and 548nm) and red (645 and 742nm) emissions upon excited at 452nm wavelength. The emission peaks at ∼742 and 645nm was associated with the transitions of (5)F4→(5)I7 and (5)F5→(5)I8 respectively. The higher energy bands located at 540 and 548nm were associated with (5)F4, (5)S2→(5)I8 transitions. Thermoluminescence (TL) studies of γ-irradiated YAlO3:Ho(3+) (1-5mol%) show two glow peaks at 223 and 325°C recorded at a heating rate of 2.5°Cs(-1). The 223°C glow peak follow linear behavior up to 1kGy and after that, it showed sub-linearity. Up to 1kGy, the phosphor is quite useful in radiation dosimetry. The kinetic parameters (E, b and s) were estimated from glow peak shape method. The CIE coordinate values lies within the green region. Therefore, the present phosphors may have potential application in WLEDs as green phosphor.

MgO:Eu3+ red nanophosphor: low temperature synthesis and photoluminescence properties

Nanoparticles of Eu(3+) doped (0-9 mol%) MgO were prepared using low temperature (400°C) solution combustion technique with metal nitrate as precursor and glycine as fuel. The powder X-ray diffraction (PXRD) patterns of the as-formed products show single cubic phase and no further calcination was required. The crystallite size was obtained using Scherer's formula and was found to be 5-6 nm. The effect of Eu(3+) ions on luminescence characteristics of MgO was studied and the results were discussed in detail. These phosphors exhibit bright red emission upon 395 nm excitation. The characteristic photoluminescence (PL) emission peaks at ∼580, 596, 616, 653, 696 and 706 nm ((5)D0→(7)Fj=0, 1, 2, 3, 4) were recorded due to Eu(3+) ions. The electronic transition corresponding to (5)D0→(7)F2 of Eu(3+) ions (616 nm) was stronger than the magnetic dipole transition corresponding to (5)D0→(7)F1 of Eu(3+) ions (596 nm). The international commission on illumination (CIE) chromaticity co-ordinates were calculated from emission spectra, the values (x, y) were very close to national television system committee (NTSC) standard value of red emission. Therefore the present phosphor was highly useful for display applications.

CaTiO3:Eu3+ red nanophosphor: low temperature synthesis and photoluminescence properties

Nanoparticles of Eu3+ doped (1-9 mol%) CaTiO3 were prepared using low temperature (500°C) solution combustion technique using metal nitrates as precursors and urea as fuel. The powder X-ray diffraction patterns of the as-formed products show single orthorhombic phase. The crystallite size was estimated using Scherrer's method and found to be in the range 40-45 nm. The effect of Eu3+ ions on luminescence characteristics of CaTiO3 was studied and the results were discussed in detail. The phosphors exhibit bright red emission upon 398 nm excitation. The characteristic emission peaks recorded at ∼540, 593, 615, 653, 696 and 706 nm (5D0→7Fj=0,1,2,3,4,5) were attributed to Eu3+ ions. The electronic transition corresponding to 5D0→7F2 (615 nm) was stronger than the magnetic dipole transition 5D0→7F1 of Eu3+ ions (596 nm). The CIE chromaticity co-ordinates were calculated from emission spectra, the values (x,y) very close to NTSC standard value of red emission. Therefore, the present phosphors were highly useful for display applications.

Structural, EPR, optical and magnetic properties of α-Fe₂O₃ nanoparticles

α-Fe(2)O(3) nanoparticles were synthesized by a low temperature solution combustion method. The structural, magnetic and luminescence properties were studied. Powder X-ray diffraction (PXRD) pattern of α-Fe(2)O(3) exhibits pure rhombohedral structure. SEM micrographs reveal the dumbbell shaped particles. The EPR spectrum shows an intense resonance signal at g≈5.61 corresponding to isolated Fe(3+) ions situated in axially distorted sites, whereas the g≈2.30 is due to Fe(3+) ions coupled by exchange interaction. Raman studies show A(1g) (225 cm(-1)) and E(g) (293 and 409 cm(-1)) phonon modes. The absorption at 300 nm results from the ligand to metal charge transfer transitions whereas the 540 nm peak is mainly due to the (6)A(1)+(6)A(1)→(4)T(1)(4 G)+(4)T(1)(4 G) excitation of an Fe(3+)-Fe(3+) pair. A prominent TL glow peak was observed at 140°C at heating rate of 5 °Cs(-1). The trapping parameters namely activation energy (E), frequency factor (s) and order of kinetics (b) were evaluated and discussed.

CdSiO₃:Pr³⁺ nanophosphor: synthesis, characterization and thermoluminescence studies

A series of Pr(3+) (1-9 mol%) doped CdSiO(3) nanophosphors have been prepared for the first time by a low temperature solution combustion method using oxalyldihydrizide (ODH) as a fuel. The final product was characterized by Powder X-ray diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The average crystallite size was calculated using Debye-Scherrer's formula and Williamson-Hall (W-H) plots and found to be in the range 31-37 nm. The optical energy band gap (E(g)) of undoped for Pr(3+) doped samples were estimated from Tauc relation which varies from 5.15-5.36 eV. Thermoluminescence (TL) properties of Pr(3+) doped CdSiO(3) nanophosphor has been investigated using γ-irradiation in the dose range 1-6 kGy at a heating rate of 5 °C s(-1). The phosphor shows a well resolved glow peak at ∼171 °C along with shouldered peak at 223 °C in the higher temperature side. It is observed that TL intensity increase with increase of Pr(3+) concentration. Further, the TL intensity at 171 °C is found to be increase linearly with increase in γ-dose which is highly useful in radiation dosimetry. The kinetic parameters such as activation energy (E), frequency factor (s) and order of kinetics was estimated by Luschiks method and the results are discussed.

YAlO3:Cr3+ nanophosphor: synthesis, photoluminescence, EPR, dosimetric studies

YAlO(3):Cr(3+) (0.1 mol%) nanophosphor has been synthesized by low temperature solution combustion method. The X-ray diffraction studies reveal an orthorhombic structure. Transmission electron microscopy reveals that the particles are spherical in shape with nano-size ~40-65 nm. Electron paramagnetic resonance (EPR) spectrum shows a resonance signal with effective g value at g=1.978 which can be attributed to the exchange coupled Cr(3+) ion pairs in weakly distorted sites. The photoluminescence spectrum shows an intense doublet at 677 nm and 694 nm (R lines) assigned to spin-forbidden (2)E(g)→(4)A(2)(g) transition of Cr(3+) ions. EPR and PL studies reveal that the Cr(3+) ions occupy Al(3+) sites in YAlO(3). The interesting feature reported in this work concerns the linearity with gamma dose in the wide range (0.1-6 kGy). Prominent TL glow peaks at 226 °C and 346 °C were observed for both γ and UV-rays respectively. It is observed that the peaks at 226 °C and 346 °C eventually show a linear response up to 5 kGy which makes them a candidate for high dose dosimetry of ionizing radiation. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped and Cr doped samples were determined using Chens glow peak shape method and the results are discussed in detail.

Effect of different fuels on structural, thermo and photoluminescent properties of Gd2O3 nanoparticles

Gd(2)O(3) nanoparticles (27-60 nm) have been synthesized by the low temperature solution combustion method using citric acid, urea, glycine and oxalyl dihydrazide (ODH) as fuels in a short time. The structural and luminescence properties have been carried out using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Raman, UV-Vis, photoluminescence (PL) and thermoluminescence (TL) techniques. The optical band gap values were estimated for as formed and 800 °C calcined samples. The band gap values in as-formed and calcined samples were found to be in the range 4.89-5.59 eV. It is observed that, the band gap values are lower for as-formed products and it has been attributed to high degree of structural defects. However, in calcined samples, structure becomes more order with reduced structure defects. Upon 270 nm excitation, deep blue UV-band at ~390nm along with blue (420-482 nm), green (532 nm) and red emission (612 nm) was observed. The 390 nm emission peak may be attributed to recombination of delocalized electron close to the conduction band with a single charged state of surface oxygen vacancy. TL measurements were carried out on Gd(2)O(3) prepared by different fuels by irradiating with γ-rays (1 kGy). A well resolved glow peak at 230 °C was observed for all the samples. It is observed that TL intensity is found to be higher in for urea fuel when compared to others. From TL glow curves the kinetic parameters were estimated using Chen's peak shape method and results are discussed in detail.

Structural, EPR, optical and Raman studies of Nd2O3:Cu2+ nanophosphors

Nanocrystalline Nd(2)O(3):Cu(2+) (2mol %) phosphors have been prepared by a low temperature solution combustion technique. Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd(2)O(3) (900°C, 3h) and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of as-formed and Cu(2+) doped Nd(2)O(3) phosphors show that the particles are irregular in shape and porous in nature. TEM results also confirm the nature and size of the particles. The EPR spectrum exhibits two resonance signals with effective g values at g(ǀǀ)≈2.12 and g(⊥)≈2.04. The g values indicate that the site symmetry of Cu(2+) ions is octahedral symmetry with elongated tetragonal distortion. Raman studies show major peaks, which are assigned, to F(g) and combination of A(g)+E(g) modes. It is observed that the Raman peaks and intensity have been reduced in Cu(2+) doped samples. UV-Visible absorption spectra exhibit a strong and broad absorption band at ∼240nm. Further, the absorption peak shifts to ∼14nm in Cu(2+) doped samples. The optical band gap is estimated to be 5.28eV for Cu doped Nd(2)O(3) nanoparticles which are higher than the bulk Nd(2)O(3) (4.7eV). This can be attributed to the quantum confinement effect of the nanoparticles.

Thermoluminescence and EPR studies of nanocrystalline Nd₂O₃:Ni²⁺ phosphor

Nanocrystalline Nd(2)O(3):Ni(2+) (2 mol%) phosphor has been prepared by a low temperature (∼400°C) solution combustion method, in a very short time (<5 min). Powder X-ray diffraction results confirm the single hexagonal phase of nanopowders. Scanning electron micrographs show that nanophosphor has porous nature and the particles are agglomerated. Transmission electron microscopy confirms the nanosize (20-25 nm) of the crystallites. The electron paramagnetic resonance (EPR) spectrum exhibits a symmetric absorption at g≈2.77 which suggests that the site symmetry around Ni(2+) ions is predominantly octahedral. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) has been evaluated. Raman study show major peaks, which are assigned to F(g) and combination of A(g)+E(g) modes. Thermoluminescence (TL) studies reveal well resolved glow peaks at 169°C along with shoulder peak at around 236°C. The activation energy (E in eV), order of kinetics (b) and frequency factor (s) were estimated using glow peak shape method. It is observed that the glow peak intensity at 169°C increases linearly with γ-dose which suggest that Nd(2)O(3):Ni(2+) is suitable for radiation dosimetry applications.

Swift heavy ion induced structural, iono and photoluminescence properties of β-CaSiO₃:Dy³⁺ nanophosphor

CaSiO(3):Dy(3+) (1-5 mol%) nanophosphors have been prepared by a low temperature solution combustion method. The structural and luminescence (ionoluminescence; IL and photoluminescence; PL) studies have been carried out for pristine and ion irradiated samples. The XRD patterns of pristine sample show a prominent peak at (320) for the monoclinic structure of β-CaSiO(3). Upon ion irradiation, the intensity of the prominent peak is decreased at the fluence of 7.81 × 10(12)ions cm(-2) and at higher fluence of 15.62 × 10(12)ions cm(-2), the prominent peak completely vanishes. The decrease in peak intensity might be due to the stress induced point defects. On-line IL and in situ PL studies have been carried out on pelletized samples bombarded with 100 MeV Si(7+) ions with fluences in the range (7.81-15.62)×10(12)ions cm(-2). The characteristic emission peaks at 481,574, 664 and 754 nm recorded in both IL and PL are attributed to the luminescence centers activated by Dy(3+) ions. It is found that IL and PL emissions intensity decreases with increase in Si(7+) ion fluence. The decrease in intensity can be due to the destruction of Si-O-Si and O-Si-O type species present on the surface of the sample. FTIR studies also confirm the Si-O-Si and O-Si-O type species observed to be sensitive for swift heavy ion (SHI) irradiated samples.

Combustion synthesis, structural characterization, thermo and photoluminescence studies of CdSiO₃:Dy³⁺ nanophosphor

CdSiO(3):Dy(3+) (1-9mol%) nanophosphors were prepared for the first time using the solution combustion method. The process of monoclinic phase formation was investigated by PXRD, TG-DTA and FTIR. The results show that the phase formation temperature of combustion-derived monoclinic CdSiO(3) is found to be lower as compared to the powders prepared by solid-state and sol-gel methods. It was observed that the average crystallite size calculated by Debye-Scherrer's formula and Williamson-Hall (W-H) plot are well comparable and was found to be in the range of 35-70 nm. Scanning electron micrographs indicate that there exist circular microcrystalline particles. It is observed that the optical energy gap is widened with the increase of Dy(3+) ion dopant. The photoluminescence (PL) spectra exhibit characteristic transitions of Dy(3+) due to (4)F(9/2)→(6)H(15/2) (blue) and (4)F(9/2)→(6)H(13/2) (yellow) regions. The thermoluminescence (TL) glow curve of CdSiO(3):Dy(3+) nano powder exposed to UV irradiation exhibited one main peak centered at 170°C. The intensity of the main peak increases up to the dose of 20 min then it decreases. The glow curves were analyzed by the glow peak shape method and the estimated trap parameters are discussed.

Ion beam induced amorphization and bond breaking in Zn2SiO4:Eu3+ nanocrystalline phosphor

This paper reports on the ionoluminescence (IL) of Zn(2)SiO(4):Eu(3+) nanophosphors bombarded with 100 MeV Si(7+) ions with fluences in the range (3.91-21.48)×10(12) ions cm(-2). The prominent IL emission peaks recorded at 580, 590, 612, 650 and 705 nm are attributed to the luminescence centers activated by Eu(3+) ions. It is observed that IL intensity decreases and saturates with increase of Si(7+) ion fluence. Fourier transform infrared (FT-IR) studies confirm surface/bulk amorphization for a fluence of (3.91-21.48)×10(13) ions cm(-2). These results show degradation of SiO (2ν(3)) bonds present on the surface of the sample and/or due to lattice disorder produced by dense electronic excitation under heavy ion irradiation. These results are discussed in detail.

Ionoluminescence studies of natural kyanite mineral from different parts of Indian origin

Ionoluminescence (IL) studies of two natural kyanite (Al(2)SiO(5)) minerals collected from different regions of India was carried out using 120 MeV Ag(9+) ions in the fluence range of 1.50-10.5 × 10(11)ions/cm(2). Identical emission peaks were observed in both the samples at ~416, 463, 530-540 nm along with other emission peaks at ~689 nm, 706 nm (sharp) and 770 nm (broad). The sharp emission peaks at 689 nm correspond to R lines of Cr(3+) impurities and are related to transition of (2)E(g)→(4)A(2g). The sharp and broad emission peaks in the range of 706-770 nm are attributed to Fe(3+) impurities and are related to the transition of (4)T(1g)→(6)A(1g). The peak in the range of 530-540 nm is attributed to Mn(2+) impurities and is related to the transition of (4)T(1)→(6)A(1). IL peak intensity decreases with the Ag(9+) ion fluence which might be due to the thermal quenching/amorphization, caused by the ion beam irradiation. The amorphization in the sample was explained with the help of thermal spike model (TSM). These results demonstrated that IL is a very sensitive technique for impurity characterization and differentiating the origin of minerals.

Enhanced photoluminescence of Gd2O3:Eu3+ nanophosphors with alkali (M=Li+, Na+, K+) metal ion co-doping

Gd(1.95)Eu(0.04)M(0.01)O(3) (M=Li(+), Na(+), K(+)) nanophosphors have been synthesized by a low temperature solution combustion (LSC) method. Powder X-ray diffraction pattern (PXRD), scanning electron microscopy (SEM), UV-vis and photoluminescence (PL) measurements were carried out to characterize their structural and luminescent properties. The excitation and emission spectra indicated that the phosphor could be well excited by UV light (243 nm) and emit red light about 612 nm. The effect of alkali co-dopant on PL properties has been examined. The results showed that incorporation of Li(+), Na(+) and K(+) in to Gd(2)O(3):Eu(3+) phosphor would lead to a remarkable increase of photoluminescence. The PL intensity of Gd(2)O(3):Eu(3+) phosphor was improved evidently by co-doping with Li(+) ions whose radius is less than that of Gd(3+) and hardly with Na(+), K(+) whose radius is larger than that of Gd(3+). The effect of co-dopants on enhanced luminescence was mainly regarded as the result of a suitable local distortion of crystal field surrounding the Eu(3+) activator. These results will play an important role in seeking some more effective co-dopants.

Combustion synthesis, characterization and Raman studies of ZnO nanopowders

Spherical shaped ZnO nanopowders (14-50 nm) were synthesized by a low temperature solution combustion method in a short time <5 min. Rietveld analysis show that ZnO has hexagonal wurtzite structure with lattice constants a=3.2511(1) Å, c=5.2076(2) Å, unit cell volume (V)=47.66(5) (Å)(3) and belongs to space group P63mc. SEM micrographs reveal that the particles are spherical in shape and the powders contained several voids and pores. TEM results also confirm spherical shape, with average particle size of 14-50 nm. The values are consistent with the grain sizes measured from Scherrer's method and Williamson-Hall (W-H) plots. A broad UV-vis absorption spectrum was observed at ∼375 nm which is a characteristic band for the wurtzite hexagonal pure ZnO. The optical energy band gap of 3.24 eV was observed for nanopowder which is slightly lower than that of the bulk ZnO (3.37 eV). The observed Raman peaks at 438 and 588 cm(-1) were attributed to the E(2) (high) and E(1) (LO) modes respectively. The broad band at 564 cm(-1) is due to disorder-activated Raman scattering for the A(1) mode. These bands are associated with the first-order Raman active modes of the ZnO phase. The weak bands observed in the range 750-1000 cm(-1) are due to small defects.

EPR, thermo and photoluminescence properties of ZnO nanopowders

Nanocrystalline ZnO powders have been synthesized by a low temperature solution combustion method. The photoluminescence (PL) spectrum of as-formed and heat treated ZnO shows strong violet (402, 421, 437, 485 nm) and weak green (520 nm) emission peaks respectively. The PL intensities of defect related emission bands decrease with calcinations temperature indicating the decrease of Zn(i) and V(o)(+) caused by the chemisorptions of oxygen. The results are correlated with the electron paramagnetic resonance (EPR) studies. Thermoluminescence (TL) glow curves of gamma irradiated ZnO nanoparticles exhibit a single broad glow peak at ∼343°C. This can be attributed to the recombination of charge carriers released from the surface states associated with oxygen defects, mainly interstitial oxygen ion centers. The trapping parameters of ZnO irradiated with various γ-doses are calculated using peak shape method. It is observed that the glow peak intensity increases with increase of gamma dose without changing glow curve shape. These two characteristic properties such as TL intensity increases with gamma dose and simple glow curve structure is an indication that the synthesized ZnO nanoparticles might be used as good TL dosimeter for high temperature application.

EPR and photoluminescence studies of ZnO:Mn nanophosphors prepared by solution combustion route

Nanocrystalline ZnO:Mn (0.1 mol%) phosphors have been successfully prepared by self propagating, gas producing solution combustion method. The powder X-ray diffraction of as-formed ZnO:Mn sample shows, hexagonal wurtzite phase with particle size of ∼40 nm. For Mn doped ZnO, the lattice parameters and volume of unit cell (a=3.23065 Å, c=5.27563 Å and V=47.684 (Å)(3)) are found to be greater than that of undoped ZnO (a=3.19993 Å, c=5.22546 Å and V=46.336 (Å)(3)). The SEM micrographs reveal that besides the spherical crystals, the powders also contained several voids and pores. The TEM photograph also shows the particles are approximately spherical in nature. The FTIR spectrum shows two peaks at ∼3428 and 1598 cm(-1) which are attributed to O-H stretching and H-O-H bending vibration. The PL spectra of ZnO:Mn indicate a strong green emission peak at 526 nm and a weak red emission at 636 nm corresponding to (4)T(1)→(6)A(1) transition of Mn(2+) ions. The EPR spectrum exhibits fine structure transition which will be split into six hyperfine components due to (55)Mn hyperfine coupling giving rise to all 30 allowed transitions. From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed. The magnitude of the hyperfine splitting (A) constant indicates that there exists a moderately covalent bonding between the Mn(2+) ions and the surrounding ligands. The number of spins participating in resonance (N), its paramagnetic susceptibility (χ) have been evaluated.

Synthesis, characterization and photoluminescence properties of CaSiO3:Eu3+ red phosphor

CaSiO3:Eu3+ (1-5 mol%) red emitting phosphors have been synthesized by a low-temperature solution combustion method. The phosphors have been well characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and optical spectroscopy. PXRD patterns reveal monoclinic CaSiO3 phase can be obtained at 900°C. The SEM micrographs show the crystallites with irregular shape, mostly angular. Upon 254 nm excitation, the phosphor show characteristic fluorescence 5D0→7FJ (J=0, 1, 2, 3, 4) of the Eu3+ ions. The electronic transition located at 614 nm corresponding to 5D0→7F2 of Eu3+ ions, which is stronger than the magnetic dipole transition located at 593 nm corresponding to 5D0→7F1 of Eu3+ ions. Different pathways involved in emission process have been studied. Concentration quenching has been observed for Eu3+ concentration>4 mol%. UV-visible absorption shows an intense band at 240 nm in undoped and 270 nm in Eu3+ doped CaSiO3 which is attributed to oxygen to silicon (O-Si) ligand-to-metal charge-transfer (LMCT) band in the SiO3(2-) group. The optical energy band gap is widened with increase of Eu3+ ion dopant.

Photoluminescence studies of 100 MeV Ni8+ ion irradiated Al2O3 single crystals

We present the results of photoluminescence (PL) measurements on 100 MeV Ni(8+) ion irradiated Al(2)O(3) single crystals in the fluence range 1x10(11) to 5x10(12) ions/cm(2). A sharp PL peaks at approximately 693, 695, 707 and 730 nm are recorded with an excitation of 442 nm He-Cd laser beam. The sharp emission peaks at 693 and 695 nm are attributed to R(2) and R(1) lines of Cr(3+) ions, and they are related to the transition from (2)E(g)-->(4)A(2g). The weaker sharp peaks called N lines appear at approximately 707 nm and its origin is ascribed due to closely coupled pairs of Cr(3+) ions. The longer wavelength part of the PL spectra at approximately 730 nm may be due to increase of groups of more than two Cr(3+) ions. It is observed that the broad emission band (450-650 nm) consists of four bands centered at 470, 518, 547 and 618 nm, respectively. The 470, 518 and 547 nm bands are corresponding to F(2)(+), F(2) and F(2)(2+) defect center, respectively. It is observed that the PL intensity of F(2), F(2)(2+), R and N lines increases with Ni(8+) ion fluence. This can be attributed to increase in concentration of color centers responsible for luminescence through radiative recombination.

Damage creation in swift heavy ion-irradiated calcite single crystals: Raman and infrared study

Raman and Infrared studies were carried out on pristine and 100 MeV Ag(8+) ion irradiated calcite single crystals in the fluence range 1 x 10(11) to 1 x 10(13)ions/cm(2). Raman and Infrared modes were assigned according to factor theory analysis. It is observed that the intensities of the Raman and infrared bands decrease with increase of ion fluence. The decrease of these bands is attributed to breakage of carbonate ions and other details are discussed.

Solution combustion derived nanocrystalline Zn2SiO4:Mn phosphors: A spectroscopic view

Manganese doped nanocrystalline willemite powder phosphors Zn(2-x)Mn(x)SiO(4) (0.1<or=x<or=0.5) have been synthesized by a low-temperature initiated, self-propagating, gas producing solution combustion process. The phosphors have been characterized by using x-ray diffraction (XRD), energy dispersive spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and photo luminescence (PL) spectroscopic techniques. The lattice parameters calculated from XRD confirm that Zn(2-x)Mn(x)SiO(4) has a rhombohedral space group R3H. The XRD patterns confirm that Zn(2-x)Mn(x)SiO(4) phosphor samples undergo a phase transformation from beta-willemite to alpha-willemite phase at 950 degrees C. The EPR spectra of Mn(2+) ions exhibit resonance signals at g approximately = 3.24 and g approximately = 2.02, with a sextet hyperfine structure centered around g approximately = 2.02. The EPR signals of Mn(2+) give a clear indication of the presence of two different Mn(2+) sites. The magnitude of the hyperfine splitting (A) indicates that the Mn(2+) is in an ionic environment. The number of spins participating in resonance (N), the paramagnetic susceptibility (chi), and the zero-field splitting parameter (D) have been evaluated as function of x. It is interesting to observe that the variation of N with temperature obeys Boltzmann. The paramagnetic susceptibility is calculated from the EPR data at various temperatures and the Curie constant and Curie paramagnetic temperature was evaluated from the 1/chi versus T graph. The luminescence of Mn(2+) ion in Zn(2)SiO(4) shows a strong green emission peak around 520 nm from the synthesized phosphor particles under UV excitation (251 nm). The luminescence is assigned to a transition from the upper (4)T(1)-->(6)A(1) ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.

Diformylhydrazine as analytical reagent for spectrophotometric determination of iron(II) and iron(III)

The bidentate ligand diformylhydrazine (OHC-HN-NH-CHO), DFH, combines with iron(II) and iron(III) in alkaline media in the pH range 7.3-9.3 to form an intensely colored red-purple iron(III) complex with an absorption maximum at 470 nm. Beer's law is obeyed for iron concentrations from 0.25 to 13 microg mL(-1). The molar absorptivity was in the range 0.3258x10(4)-0.3351x10(4) L mol(-1) cm(-1) and Sandell's sensitivity was found to be 0.0168 microg cm(-2). The method has been applied to the determination of iron in industrial waste, ground water, and pharmaceutical samples.