Crystal Phase Refinement and Optical Features of Highly Efficient Green Light Radiating Ca9Y(VO4)7: Er3+ Nanophosphors for Emerging Solid-state Lighting Applications

Ca9Y(VO4)7 phosphor activated with Er3+ ions have been developed by the urea-aided solution combustion technique. XRD profiles assisted with Rietveld refinement executed over-developed Er3+-activated Ca9Y(VO4)7 powder, revealed a trigonal phase with the R3c space group. The electron microscope techniques namely TEM and SEM characterize the size and surface-linked qualities of the developed nanopowder, respectively. The uniform distribution of various elements in the nanocrystalline sample is authenticated by an energy-dispersive spectroscopy (EDS) system. The Eg (band gap) value of 3.64 eV for Ca9Y0.9Er0.1(VO4)7 and 3.74 eV for Ca9Y(VO4)7 has been estimated. Upon 382 nm excitation, Er3+: Ca9Y(VO4)7 phosphor gives rise to the bright green emission owing to the 4S3/2 → 4I15/2 transition. The concentration quenching after 10 mol% composition of trivalent erbium ions is attributed to dipole-dipole interlinkages in accordance with Dexter's theory. The radiative lifetime (1.1083 ms), non-radiative rates (0.2079 ms- 1), quantum efficiency (79%), along with colorimetric parameters i.e. CIE x (= 0.2577), y (= 0.4566), and CCT quantities offer Ca9Y0.9Er0.1(VO4)7 as a proficient green radiating nanomaterial for RGB phosphors in solid-state applications.

Exploration of Photoluminescence, Colorimetric, and Decay Performance of Sm-activated CaWO4 Ceramic

This paper represents structure, photoluminescence, and colorimetric investigations of Sm-activated CaWO4 ceramic made with the help of a solid-state reaction process. Structures of the ceramics are examined through X-ray diffraction spectroscopy. It indicates that these materials have a tetragonal structure and I41/a space group without having any other secondary phase. Energy band gaps are increased with the higher concentrations of Sm dopants. Photoluminescence analyses show that concentration quenching is found at x = 0.02 Sm incorporated CaWO4. The critical distance of energy transfer is obtained as about 20 Å. Q-value is observed approximately equal to 6 which denotes that dipole-dipole interactions occur in the materials that create the critical energy transfer distance in them. Chromaticity values are described in that the ceramics emit orange-red color as well as excellent colorimetric parameters. Quantum efficiency of x = 0.02 Sm composition in CaWO4 is measured under 405 nm EX wavelength. Photoluminescence decay behaviors are observed and average lifetime values are evaluated.

Eu3+ doped CaWO4 nanophosphor for high sensitivity optical thermometry

Eu3+ doped calcium tungstate phosphors were obtained by using sodium citrate as chelating agent in hydrothermal process. The structure and morphology of the samples were indicated by XRD and the FE-SEM. The samples prepared by us are scheelite structure. In addition, the particle size of sample decreases with sodium citrate dosage increasing, and finally reaches the nanoscale. The average particle size is 90 nm. The temperature measurement properties of phosphors were tested. It can be seen from test results that the thermal quenching behavior of Eu3+ and WO42- luminescence has obvious difference. Hence, the FIR of Eu3+ and WO42- can be used to express temperature. The maximum relative sensitivity increases with the decrease of particle size and the maximum is 4.3% K-1 (303 K, 90 nm). Moreover, the color of sample luminescence altered continuously from blue to pink-red as the temperature increased. The luminous color of the sample can be used to roughly estimate the temperature. Therefore, the CaWO4: Eu3+ nanophosphor are promising materials for optical thermometry.

Estimation of spectroscopic parameters and TL glow curve analysis of Eu3+-activated CaY2O4 phosphor

The solid-state reaction method was utilised to create a down-conversion phosphor in an air environment in CaY2O4:Eu3+ nanocrystalline material. The calcination temperature was set at 1000 °C, and the sintering temperature was set at 1300 °C. Following annealing, confirmation of the crystallinity quality of the phosphor was accomplished by the use of X-ray diffraction analysis. The particle size was predicted to be 43.113 nm using Scherrer's formula. To produce down-conversion luminescence spectra, an excitation wavelength of 247 nm was applied with a fluorescence spectrophotometer. The PL got increasingly intense as the concentration of the dopant increased. The maximum intensity was measured at 2.0 mol% of Eu3+ ion, which gradually decreased as the concentration increased because of concentration quenching. To analyse spectrophotometric peak determinations, the approach developed by the Commission Internationale de l'Éclairage (CIE) was used. Thermoluminescence (TL) glow curve analysis of the CaY2O4:Eu3+-doped phosphor manufactured here revealed a wide TL centred at 225 °C, which comprised of so many peaks that may be extracted by the computerised glow curve deconvolution (CGCD) approach using glow-fit software. The associated kinetic parameters were then determined. The prepared phosphor may be useful for application in various display devices upon excitation by 247 nm; the prominent 613 nm peak of the Eu3+ ion (5D0 → 7F2) electric dipole transition features a red component. CaY2O4:Eu3+ phosphors show promise as materials for potential use in phosphor-converted white LEDs in the field of solid-state lighting technology. The linear connection that the TL glow curve has with UV dose provides evidence for its possible use in dosimetry.

Calcium Tungstate Doped with Rare Earth Ions Synthesized at Low Temperatures for Photoactive Composite and Anti-Counterfeiting Applications

A precursor was prepared using a co-precipitation method to synthesize crystalline calcium tungstate. The prepared precursor was dried in an oven at 80 °C for 18 h. The dried powders, prepared without a heat treatment process, were observed in XRD analysis to be a crystalline CaWO4 phase, confirming that the synthesis of crystalline CaWO4 is possible even at low temperature. To use this crystalline CaWO4 as a light emitting material, rare earth ions were added when preparing the precursor. The CaWO4 powders doped with terbium (Tb3+) and europium (Eu3+) ions, respectively, were also observed to be crystalline in XRD analysis. The luminescence of the undoped CaWO4 sample exhibited a wide range of 300~600 nm and blue emission with a central peak of 420 nm. The Tb3+-doped sample showed green light emission at 488, 545, 585, and 620 nm, and the Eu3+-doped sample showed red light emission at 592, 614, 651, and 699 nm. Blue, green, and red CaWO4 powders with various luminescence properties were mixed with glass powder and heat-treated at 600 °C to fabricate a blue luminescent PiG disk. In addition, a flexible green and red light-emitting composite was prepared by mixing it with a silicone-based polymer. An anti-counterfeiting application was prepared by using the phosphor in an ink, which could not be identified with the naked eye but can be identified under UV light.

Photoluminescence, TGA/DSC and photocatalytic activity studies of Dy3+ doped SrY2O4 nanophosphors

Dy3+:SrY2O4 nanophosphors were prepared via a solution combustion method using glycine as an organic fuel. The structural, optical, and thermal properties of the nanophosphors were studied. Strain and crystal size were calculated via W-H analysis. The direct energy band gap is nearly 4.9 eV and photocatalytic studies reveal that Rh-B degradation of almost 50% can be achieved.

Samarium-Activated La2Hf2O7 Nanoparticles as Multifunctional Phosphors

Recent developments in the field of designing novel nanostructures with various functionalities have pushed the scientific world to design and develop high-quality nanomaterials with multifunctional applications. Here, we propose a new kind of doped metal oxide pyrochlore nanostructure for solid-state phosphor, X-ray scintillator, and optical thermometry. The developed samarium-activated La₂Hf₂O₇ (LHOS) nanoparticles (NPs) emit a narrow and stable red emission with lower color temperature and adequate critical distance under near-UV and X-ray excitations. When the LHOS NPs are exposed to an energetic X-ray beam, the Sm³⁺ ions situated at the symmetric environment get excited along with those located at the asymmetric environment, which results in a low asymmetry ratio of Sm³⁺ under radioluminescence compared to photoluminescence. High activation energy and adequate thermal sensitivity of the LHOS NPs highlight their potential as a thermal sensor. Our results indicate that these Sm³⁺-activated La₂Hf₂O₇ NPs can serve as a multifunctional UV, X-ray, and thermographic phosphor.

Sm3+ doped calcium orthovanadate Ca3(VO4)2 - A spectral study

Sm³⁺-doped vanadate-based phosphors, Ca_3-x (VO₄)₂:Sm_x(x = 0.005 ≤ x ≤ 0.095), were synthesized by the citrate-based sol-gel method. The samples were characterized with XRD, SEM, diffuse reflectance and photoluminescence spectroscopy, aiming at the development of phosphor-converted wLED applications. Using diffuse reflectance spectra and the Kubelka-Munk function, the band gap energy was calculated to be 3.28 eV for the Ca_2.95(VO₄)₂:Sm_0.05 phosphor. Observation of the photoluminescence excitation spectra revealed a broadband excitation from the distorted VO₄ tetrahedron and a few narrow peaks from the 4f-4f intra-configuration transitions of the Sm³⁺ ions. Upon 404 nm excitation, ⁴G_5/2 → ⁶H_5/2 (564 nm), ⁴G_5/2 → ⁶H_7/2 (601 nm), ⁴G_5/2 → ⁶H_9/2 (648 nm) and ⁴G_5/2 → ⁶H_11/2 (701 nm) transitions were observed. The optimum Sm³⁺ concentration for the studied phosphor is 0.05 mol, and the estimated critical distance between Sm³⁺ ions (R_c) is 19.1 Å. The observed quenching of Sm³⁺ emission is attributed to the dipole-dipole interactions. The possible cross-relaxation process between neighboring Sm³⁺ ions was discussed in detail. The CIE coordinates were calculated for all the samples, and they set on the orange region of CIE diagram. In addition, pure orange color emission was observed under 365 nm UV lamp. The results suggest that the Ca₃(VO₄)₂:Sm³⁺ phosphor could be a good candidate for the orange emitting component for wLED applications.

Tunable Luminescence in Sr2MgSi2O7:Tb3+, Eu3+Phosphors Based on Energy Transfer

A series of Tb³⁺, Eu³⁺-doped Sr₂MgSi₂O₇ (SMSO) phosphors were synthesized by high temperature solid-state reaction. X-ray diffraction (XRD) patterns, Rietveld refinement, photoluminescence spectra (PL), and luminescence decay curves were utilized to characterize each sample’s properties. Intense green emission due to Tb³⁺⁵D₄→⁷F₅ transition was observed in the Tb³⁺ single-doped SMSO sample, and the corresponding concentration quenching mechanism was demonstrated to be a diople-diople interaction. A wide overlap between Tb³⁺ emission and Eu³⁺ excitationspectraresults in energy transfer from Tb³⁺ to Eu³⁺. This has been demonstrated by the emission spectra and decay curves of Tb³⁺ in SMSO:Tb³⁺, Eu³⁺ phosphors. Energy transfer mechanism was determined to be a quadrupole-quadrupole interaction. And critical distance of energy transfer from Tb³⁺ to Eu³⁺ ions is calculated to be 6.7 Å on the basis of concentration quenching method. Moreover, white light emission was generated via adjusting concentration ratio of Tb³⁺ and Eu³⁺ in SMSO:Tb³⁺, Eu³⁺ phosphors. All the results indicate that SMSO:Tb³⁺, Eu³⁺ is a promising single-component white light emitting phosphor.

Multicolor Tuning in Room-Temperature Self-Activated Ca2 Nb2 O7 Submicroplates by Lanthanide Doping

Self-activated phosphors are capable of generating optical emissions from the internal ion groups of host lattice before externally introducing luminescent ions. However, numerous self-activated phosphors only show luminescence at low temperature due to the thermally activated energy migration among ion groups at room temperature, severely confining their application conditions. In this letter, we propose a strategy to converting the low-temperature luminescence to a room-temperature one through changing the synthesis conditions to induce structural distortions and thus to limit energy migration. Room-temperature self-activated luminescence of Ca₂ Nb₂ O₇ was accordingly achieved in submicroplates synthesized using the sol-gel method. By further coupling the blue broadband emission from Ca₂ Nb₂ O₇ submicroplates with the characteristic luminescence of Ln³⁺ (Pr³⁺ , Sm³⁺ , and Dy³⁺ ) dopants, multicolor emissions were successively tuned through adjusting the concentration of Ln³⁺ . Our results are expected to expand the scope of designing room-temperature self-activated phosphors and tuning multicolor emission.

Facile hydrothermal synthesis and pulsed laser deposition of Ca0.5Y1−x(WO4)2:xEu3+ phosphors: investigations on the luminescence, Judd–Ofelt analysis and charge compensation mechanism

PL emission spectra of Ca_0.5Y_1−x(WO₄)₂:xEu³⁺ for powder and thin film phosphors, and PL spectra of Ca_0.5Y_1−x(WO₄)₂:xEu³⁺ co-doped with alkali metal ions.

Tailoring light emission properties and optoelectronic and optothermal responses from rare earth-doped bismuth oxide for multifunctional light shielding, temperature sensing, and photodetection

We have developed an all-purpose material with tunable light emission property and controllable optoelectronic and optothermal response processes.

Multi-color luminescence properties and energy transfer behaviour in host-sensitized CaWO4:Tb3+,Eu3+phosphors

A series of host-sensitized and color-tunable CaWO₄:Tb³⁺,Eu³⁺phosphors have been successfully synthesizedviathe high-temperature solid-state reaction route and their photoluminescence properties and energy transfer mechanism have been carefully investigated.

Lanthanide-activated scheelite nanocrystal phosphors prepared by the low-temperature vapor diffusion sol–gel method

The high degree of synthetic flexibility inherent to the vapor diffusion sol–gel method has enabled the synthesis of a CaWO₄:(Eu,Tb) dual-sensitized white light emitting nanocrystal phosphor.

Improved photo-luminescence behaviour of Eu3+ activated CaMoO4 nanoparticles via Zn2+ incorporation

Zn²⁺ (0, 2, 5, 7 and 10 at%) co-doped CaMoO₄:2Eu³⁺ nanophosphors have been synthesized via the polyol method using ethylene glycol (EG) as both capping agent and reaction medium at 150 °C.