Novel Eu3+-Doped Glasses in the MoO3-WO3-La2O3-B2O3 System: Preparation, Structure and Photoluminescent Properties

Novel multicomponent glasses with nominal compositions of (50-x)MoO3:xWO3:25La2O3:25B2O3, x = 0, 10, 20, 30, 40, 50 mol% doped with 3 mol % Eu2O3 were prepared using a conventional melt-quenching method. Their structure, thermal behavior and luminescent properties were investigated by Raman spectroscopy, differential thermal analysis and photoluminescence spectroscopy. The optical properties of the glasses were investigated by UV-vis absorption spectroscopy and a determination of the refractive index. Physical parameters such as density, molar volume, oxygen molar volume and oxygen packing density were determined. The glasses are characterized by a high glass transition temperature. Raman analysis revealed that the glass structure is built up mainly from tetrahedral (MoO4)2- and (WO4)2- units providing Raman bands of around 317 cm-1, 341-352 cm-1, 832-820 cm-1 and 928-935 cm-1. At the same time, with the replacement of MoO3 with WO3 some fraction of WO6 octahedra are produced, the number of which increases with the increasing WO3 content. A strong red emission from the 5D0 level of Eu3+ ions was registered under near-UV (397 nm) excitation using the 7F0 → 5L6 transition of Eu3+. Photoluminescence (PL) emission gradually increases with increasing WO3 content, evidencing that WO3 is a more appropriate component than MoO3. The integrated fluorescence intensity ratio R (5D0 → 7F2/5D0 → 7F1) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu3+ in non-centrosymmetric sites. All findings suggest that the investigated glasses are potential candidates for red light-emitting phosphors.

Blue to Red Emission Tunable Bi3+ co-doped YPO4:Eu3+: Host Emission and Phase Change

Bi3+(0, 1, 3, 5, 7, 10, 12 and 15 at.%) co-doped YPO4:Eu3+ have been hydrothermally synthesized. Bi3+ (x ≥ 1 at.%) co-doping in YPO4:Eu3+ renders mixed crystalline phase of tetragonal to hexagonal. Pure tetragonal phase of Bi3+ co-doped YPO4:Eu3+ could be achieved upon annealing at 900 °C. The luminescence intensity is improved significantly upon annealing at 900 °C. This is due to the reduction of quenching pathways such as water molecules, dangling bonds, etc. The probability of magnetic dipole and electric dipole transitions is observed to be altered. As-prepared samples show near blue emission, while 900 °C annealed samples exhibit red emission, which could be a potential candidate for display, sensing and biological labelling, etc.

Glass-Ceramic Materials with Luminescent Properties in the System ZnO-B2O3-Nb2O5-Eu2O3

In this paper, the crystallization behavior of 50ZnO:47B2O3:3Nb2O3:0.5Eu2O3 (G-0 h) glass has been investigated in detail by DSC, XRD and TEM analysis. The luminescent properties of the resulting glass-ceramics were also investigated. By XRD and TEM analysis, crystallization of several crystalline phases has been proved (α-Zn3B2O6, β-Zn3B2O6 and ZnNb2O6). By calculating crystal parameters, it was found that europium ions are successfully incorporated in the β-Zn3B2O6. Photo-luminescent spectra showed increased emission in the resulting glass-ceramic samples compared to the parent glass sample due to higher asymmetry of Eu3+ ions in the obtained crystalline phases. It was established that the optimum emission intensity is registered for glass-ceramic samples obtained after 25 h heat treatment of the parent glass.

Effect of the Addition of WO3 on the Structure and Luminescent Properties of ZnO-B2O3:Eu3+ Glass

Glasses with the compositions in mol % of 50ZnO:(50 - x)B2O3:0.5Eu2O3:xWO3, x = 0, 1, 3, 5 and 10 were obtained by applying the melt-quenching method and investigated by Raman spectroscopy, DSC analysis and photoluminescence (PL) spectroscopy. Raman spectra revealed that tungstate ions incorporate into the base zinc borate glass as tetrahedral [WO4]2- groups, and octahedral [WØ4O2]2- species with four bridging and two non-bridging oxygen atoms. There are also metaborate, [BØ2O]- and pyroborate units, [B2O5]4-, in the glass networks. The glasses are characterized by good transmission in the visible region, at about 80%. Photoluminescence (PL) spectra evidenced that WO3 is an appropriate constituent for the modification of zinc borate glass structure and for enhancing the Eu3+ luminescent intensity. The most intense luminescence peak observed, at 612 nm, suggests that the glasses are potential materials for red emission.

Photoluminescence Study of Undoped and Eu-Doped Alkali-Niobate Aluminosilicate Glasses and Glass-Ceramics

In this study, the photoluminescence (PL) behavior of two aluminosilicate glass series containing alkali-niobates ranging from 0.4 to 20 mol% was investigated. The glasses exhibit an intense visible emission centered at ~18,400 cm-1 for the peralkaline series and at higher energies (~19,300 cm-1) for the metaluminous glasses. However, the photoluminescence emission intensity varies significantly with the niobate content and the bulk chemistry. PL and fluorescence lifetime measurements indicate that the broad emission bands result from the overlap of different niobate populations, whose distribution changes with niobate content. The distinct PL behavior in the two glass series was related to the structural evolution of the niobate units upon niobium addition. An enhancement of the visible emission was observed for a higher fraction of distorted [NbO6] units. Eu-doping was carried out as a structural probe of the glass network, and also to determine if these glasses could be used as potential rare earth element (REE) activators. The crystal field strength around Eu ions is strongly dependent on the bulk chemistry and the niobate content. Furthermore, the peralkaline series showed energy transfer from the host [NbO6] to Eu3+, confirming the feasibility of exploring niobate glasses and glass-ceramics as lanthanide ion-activated luminescent materials. In addition, glass-ceramics (GCs) containing alkali-niobate phases with a perovskite-like structure were developed and studied to verify the optical performance of these materials. It was verified that the bulk chemistry influences crystallization behavior, and also the photoluminescence response. The transparent GC from the metaluminous series exhibits a quenching of the Eu3+ emission, whereas an enhanced emission intensity is observed for the peralkaline GC. The latter shows a strong excitation-dependent PL emission, suggesting energy transfer and migration of electronic excitation from one Eu population to another. Additionally, Eu3+ emissions arising from the D15 and D25 excited states were observed, highlighting the low phonon energy achievable in niobo-aluminosilicate hosts.

Hydrothermal Synthesis of Rod Shaped Red Emitting Gd2O3:Eu3+ Phosphor

Simple hydrothermal method can be applied for synthesizing rod shape Gd2O3:Eu3+ phosphors. X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy are used for the characterizations of samples. Increase of Eu3+ concentration in Gd2O3:Eu3+ can cause red shift in the charge transfer band (CTB) of Eu - O. The nature of Eu3+ surroundings is asymmetric. It is ascertained from PL emission studies. The calculation of second order crystal field parameter from PL spectra corroborates the asymmetric environment of Eu3+. PL emission and decay lifetime studies confirm the existence of quenching due cross-relaxation. The quantum yield for Y2O3:Eu3+ (19 at.%) under 265 nm excitation is found to be 7%.

Exploring the effect of boron on the grain morphology change and spectral properties of Eu3+ activated barium tantalate phosphor

The effect of the grain morphology on the photoluminescence, charge transfer band, and decay properties was investigated by xEu3+, yB3+ (x = 10 mol%, y = 0, 5, 15, 30, 50, 70, and 100 mol%) co-doped BaTa2O6 ceramics fabricated by solid-state reaction. X-ray diffractions of the samples showed that the single-phase structure persisted up to 100 mol% and there was an improvement in crystallinity with increasing B3+ concentration. SEM micrographs of the Eu3+, B3+ co-doped grains showed that the flux effect of boron promotes grain growth and elongated grain shape. The PL emissions of the BaTa2O6:xEu3+, yB3+ co-doped phosphors increased up to 100 mol% B3+ concentration, and there was an increase in the intensities of the CTB energy 5D0 → 7F1 transition. The increase in PL may be attributed to the increased grain size leading to a decrease in the surface area (SA)/volume (vol) ratio with increasing B3+ concentration, as well as the improvement in crystallinity. However, the decrease in asymmetry ratio was related to the occupation of centrosymmetric (B) sites and the transformation from a rounded/irregular-like to an elongated/rod-like grain shape which has an increasing effect on the SA/vol ratio. The decreasing trend of the Judd-Ofelt parameters (Ω2, and Ω4) with the increase in boron was related to a high local symmetry of Eu3+ sites, and an increase in the electron density of the surrounding ligands, respectively. The increase in boron led to longer decays in the observed lifetime with bi-exponential characteristics. The CIE diagram and UV lamp photographs of the phosphors showed a color transition from red to orange associated with the increasing magnetic dipole transition. This study may provide an alternative perspective and new strategies to describe the control of grain morphology and luminescence concerning RE-doped phosphors.

Studies on a novel SrZr2 CaLa2 O8 :Eu3+ phosphor for lighting applications emitting direct white light

Direct white light emitting phosphors play a significant role in the display industry due to their ability to improve the quality, efficiency, and versatility of lighting sources used in most of the displays. The currently investigated phosphor SrZr2 CaLa2 O8 :Eu3+ was prepared by a conventional solid-state reaction method. It has been observed that the stoichiometric ratio of all precursors plays an important role in determining the characteristics of the final phosphor. From X-ray diffraction (XRD) analysis, the phosphor was observed to have a hexagonal phase and a crystal size of ~28 nm. Scanning electron microscopy (SEM) observations revealed a cluster of rod-like structures with an average diameter of ~0.2 μm. The excitation peak maximum observed at 280 nm is due to charge transfer between Eu3+ -O2- ions. The energy transitions 7 F0  → 5 L6 and 7 F0  → 5 D2 are responsible for the appearance of other excitation peaks at ultraviolet (UV) (395 nm), blue (~467 nm), green (~540 nm), orange (~590 nm), and red (~627 nm) attributed to 5 D0  → 7 FJ (J = 0-4) transitions of europium ion (Eu3+ ). The Commercial International de I'Eclairage (CIE) chromaticity coordinates were estimated to be (0.37, 0.0.33) and (0.67, 0.33) for the emissions corresponding to 395 and 590 nm, respectively. The characteristic emissions of Eu3+ ions allow this novel phosphor to be used to generate direct white light in light-emitting diodes (LEDs), which is otherwise difficult to achieve in single-component systems.

NaGdF4:Eu3+ nanocrystalline: an in-depth study of energy transfer processes and Judd-Ofelt analysis using the luminescence excitation spectrum

NaGdF4 nanocrystalline doped with different concentrations of Eu3+ ions were synthesized using the precipitation method. The structure and morphology of the material were investigated through the measurements of the XRD patterns and SEM images, respectively. The optical properties of the NaGdF4:Eu3+ nanocrystalline were studied in the framework of the Judd-Ofelt theory in which the Ωλ parameters were calculated by two methods: the traditional method using the luminescence spectra and the self-referenced method using the luminescence excitation spectra. In NaGdF4:Eu3+ nanocrystalline, the Gd3+ ions in the lattice act as sensitizer centers for the luminescence of Eu3+ ions under excitation at 272 and 310 nm. The energy transfer process from Gd3+ to Eu3+ causes the emission enhancement of Eu3+ ions. Upon excitation by the characteristic wavelengths of Gd3+, the luminescence efficiency of the Eu3+ ions in NaGdF4:Eu3+ is affected by two mechanisms: the emission of Gd3+ ions and the trapping of excited energy by the Eu3+ ions. The energy transfer between Eu3+ ions was also discussed in detail. This process leads to the enhancement of the luminescence bands originating from the 5D0 level. The dominant interaction between the Eu3+ ions in the energy transfer process is the dipole-dipole mechanism, which is determined by fitting the decay curve of the 5D2 level to the Inokuti-Hirayama model.

Network Structure and Luminescent Properties of ZnO-B2O3-Bi2O3-WO3:Eu3+ Glasses

In this study, we investigated the influence of Bi2O3 and WO3 on both structure and optical properties of 50ZnO:(49 - x)B2O3:1Bi2O3:xWO3; x = 1, 5, 10 glasses doped with 0.5 mol% Eu2O3. IR spectroscopy revealed the presence of trigonal BØ3 units connecting superstructural groups, [BØ2O]- metaborate groups, tetrahedral BØ4- units in superstructural groupings (Ø = bridging oxygen atom), borate triangles with nonbridging oxygen atoms, [WO4]2- tetrahedral, and octahedral WO6 species. Neutron diffraction experimental data were simulated by reverse Monte Carlo modeling. The atomic distances and coordination numbers were established, confirming the short-range order found by IR spectra. The synthesized glasses were characterized by red emission at 612 nm. All findings suggest that Eu3+ doped zinc borate glasses containing both WO3 and Bi2O3 have the potential to serve as a substitute for red phosphor with high color purity.

Low-temperature in situ preparation of Eu3+/Tb3+-doped CaMoO4/SrMoO4 nanoparticle thin films and their application in anti-counterfeiting

Rare earth-doped metal oxide thin films exhibit remarkable potential for application in anti-counterfeiting, owing to their exceptional fluorescent properties. However, the existing fabrication techniques for these rare earth-doped luminescent thin films are predominantly complex and necessitate high-temperature conditions. In light of this issue, we present a low-temperature method for in situ fabrication of luminescent Ca1-xMoO4:Eux3+ and Sr1-xMoO4:Tbx3+ nanocrystal thin films by a solution deposition process. The developed method has the advantages of simple operation, rapid and low-temperature synthesis. The optimal chemical compositions of molybdate-based luminescent films are Ca0.90MoO4:Eu0.103+ and Sr0.90MoO4:Tb0.103+. Moreover, we evaluate the practical feasibility of luminescent nanoparticle films in the field of anti-counterfeiting by combining the unique fluorescent properties of rare earth ions and designing customized fluorescent patterns.

An Ultrafast and Room-Temperature Strategy for Kilogram-Scale Synthesis of Sub-5 nm Eu3+ -doped CaMO4 Nanocrystals with a Photoluminescence Quantum Yield Exceeding 85

Rare earth-doped metal oxide nanocrystals have a high potential in display, lighting, and bio-imaging, owing to their excellent emission efficiency, superior chemical, and thermal stability. However, the photoluminescence quantum yields (PLQYs) of rare earth-doped metal oxide nanocrystals have been reported to be much lower than those of the corresponding bulk phosphors, group II-VI, and halide-based perovskite quantum dots because of their poor crystallinity and high-concentration surface defects. Here, an ultrafast and room-temperature strategy for the kilogram-scale synthesis of sub-5 nm Eu3+ -doped CaMoO4 nanocrystals is presented, and this reaction can be finished in 1 min under ambient conditions. The absolute PLQYs for sub-5 nm Eu3+ -doped CaMoO4 nanocrystals can reach over 85%, which are comparable to those of the corresponding bulk phosphors prepared by the high-temperature solid state reaction. Moreover, the as-produced nanocrystals exhibit a superior thermal stability and their emission intensity unexpectedly increases after sintering at 600 °C for 2 h in air. 1.9 kg of Eu3+ -doped CaMoO4 nanocrystals with a PLQY of 85.1% can be obtained in single reaction.

Luminescence of undoped and Eu3+ activated zinc gallate phosphor: Synthesis, unusual intense 5D0 → 7F4 red emission

A series of Eu³⁺-doped ZnGa₂O₄ samples were synthesized via the urea-glycine combustion route. Powder X-ray diffraction (XRD) was used to investigate the crystallinity of the samples, energy dispersive spectroscopy (EDS) to explore the elemental composition, Fourier transform infrared (FTIR), to observe the vibrational modes of the samples, photoluminescence (PL) to determine the luminescence properties. The XRD data prove that the samples remain single cubic structure even at high concentrations of Eu³⁺, enabling the formation of a unique emission spectrum. The active ion concentration was varied to examine the influence of concentration on luminescent properties. This study revealed a ⁵D₀ →⁷F₄ transition located at 700 nm with unusual intensity that has not been documented in the literature, which suggests that the active ion concentration can influence the luminescent characteristics of the phosphors. The increasing Eu³⁺ content increases the number of Eu³⁺ ions in ZnGa₂O₄ host lattice, which enhances the luminescence efficiency of the phosphor. However, beyond a certain level of Eu³⁺content (i.e., 3 wt% Eu³⁺), the number of Eu³⁺ ions becomes excessive, resulting in a reduction in luminescence efficiency due to concentration quenching. The dipole dipole interaction is elucidated to play a prominent role in the mechanism of Eu³⁺ quenching in the ZnGa₂O₄. An assessment of color coordinates based on emission spectra reveals that the coordinates shift from blue to the white light region, and then to red as Eu³⁺ content increases. This suggests that there is a substantial relationship between the Eu³⁺ concentration and the measured color coordinates.

A highly selective optical sensor Eu-BINAM for assessment of high sensitivity cardiac troponin tumor marker in serum of cancer patients

A novel, easy, touchy and selective spectrofluorimetric technique has been successfully applied for sensitive determination of High Sensitivity Cardiac Troponin (TNHS I) in the serum samples of patients suffering malignant tumors through the usage of optical sensor Eu^3+-BINAM complex. The technique is primarily based on quenching of the Eu³⁺-BINAM complex's luminescence intensity upon introducing various concentrations of High Sensitivity Cardiac Troponin (TNHS I). The synthesis and characterization of the optical sensor was performed via absorption and emission. The sensor was also adapted to offer excitation at 394 nm in acetonitrile at pH 7.5. Concentration of High Sensitivity Cardiac Troponin (TNHS I) in serum samples was found to be proportional to the luminescence intensity quenching of the Eu³⁺-BINAM complex, most prominently at λ_em = 618 nm. The limit of the dynamic range is 4.26 × 10^-4 to 2 ng/mL. The limit of detection and quantitation were calculated to be 1.35 and 4.10 ng/mL, respectively. The suggested analytical approach proved its applicability, simplicity and comparatively interference- free. The technique was effectively recruited to quantify High Sensitivity Cardiac Troponin (TNHS I) in human serum samples. The proposed technique could be further extended to evaluate some biomarkers associated with malignancy related diseases in human.

Boron doping effect on the structural, spectral properties and charge transfer mechanism of orthorhombic tungsten bronze β-SrTa2O6:Eu3+ phosphor

In the study, the effect of boron doping on spectral properties and CTB mechanism was investigated by using Eu³⁺ doped orthorhombic β-SrTa₂O₆. A phosphor series of Eu³⁺ doped SrTa₂O₆, and Eu³⁺ and B³⁺ co-doped SrTa₂O₆ polycrystals were fabricated by solid-state reaction at 1400 °C for 20 h in an air atmosphere. The X-ray diffractions of the main phase structure for all the ceramics maintained up to 10 mol% Eu³⁺ concentration, while the increase of XRD intensity for Eu³⁺ and B³⁺ co-doped samples was attributed to somewhat improvement of crystallization. SEM morphologies of grains showed that the presence of boron promotes agglomeration and grain growth. The doping of boron up to 20 mol% led to an increase in PL intensity, CTB energy slightly shifted to low energy, and also an increase occurred in the asymmetry ratio of the phosphor. Therefore, the low crystal field symmetry of the Eu³⁺ sites and some improvement in crystal structure properties for Eu³⁺, B³⁺ co-doped samples supported the PL increase. The trend of Judd-Ofelt parameters (Ω ₂, Ω ₄) is SrTa₂O₆:xEu³⁺, 0.1B³⁺ > SrTa₂O₆:xEu³⁺. The high Ω ₂ parameter for boron co-doped samples showed a covalent Eu-O bond character with low symmetry of Eu³⁺ environment, while the high Ω ₄ value indicated the reduction in electron density of the ligands. Some increase in the short decays of Eu³⁺, B³⁺ co-doped samples is probably due to the surface effect and low crystal field symmetry. The quantum efficiency of 0.05Eu³⁺, 0.1B³⁺ co-doped phosphor with the highest PL intensity increased by about 21% compared to that without boron.

Europium doped Sr2 YNbO6 double perovskite phosphor for photoluminescence and thermoluminescence properties

A luminescent double perovskite phosphor Sr₂ YNbO₆ doped with Eu³⁺ crystallized to the monoclinic phase and was synthesized successfully via a conventional high-temperature combustion method. The formation of the crystal structure, phase purity, and surface morphology were studied using X-ray diffraction patterns and scanning electron microscopy. The characteristic vibrations between the atoms of the functional groups present in phosphor were studied using Fourier transform infrared spectra analysis. The luminescence properties of the prepared phosphors were investigated in terms of photoluminescence (PL) and thermoluminescence (TL). PL excitation spectra exhibited charge transfer bands and the characteristic 4f⁶ transitions of Eu³⁺ . A prominent PL emission was obtained for the phosphor doped with 4 mol% Eu³⁺ under the 396 nm excitation wavelength. PL emission quenching was observed for the higher doping concentrations due to a multipole-multipole interaction. A highly intense PL emission arose due to the hypersensitive ⁵ D₀ -⁷ F₂ electric dipole transition of Eu³⁺ that dominated the emission spectra. The thermal stability of the phosphor was examined through temperature-dependent PL. The TL properties of the Sr₂ YNbO₆ double perovskites irradiated with a ⁹⁰ Sr beta source at different doses were measured. The double perovskite phosphors under study showed a linear dose-response with increasing beta dose, ranging from 1 Gy to 10 Gy. Trapping parameters of the TL glow curves were determined using Chen's peak shape method and computerized glow curve deconvolution (CGCD). CGCD fitting of the TL glow curves revealed that it was consisted of three major peaks and followed second-order kinetics. The estimated activation energies were determined using different methods and were comparable and significant.

Tunable Luminescence from Bi3+ Sensitized La2 Zr2 O7 : Eu3+ Red Nanophosphors for Display Applications

Bi³⁺ sensitized, Eu³⁺ activated La₂ Zr₂ O₇ nanophosphors are prepared successfully by simple wet chemical method. Strong blue emission of singly doped La₂ Zr₂ O₇ with Bi³⁺ ions was observed at 310 nm excitation, its wide emission spectrum has a peak maximum at 465 nm ascribed to electronic transition ³ P₁ →¹ S₀ of Bi³⁺ ions. The recorded photoluminescence spectra of x at % Eu³⁺ co-doped La₂ Zr₂ O₇ , when excited at 285 nm, the emission spectrum exhibits maximum peaks at wavelength values 615 nm, 646 nm and 665 nm which are ascribed to ⁵ D₀ →⁷ F₂ , ⁵ D₀ →⁷ F₃ and ⁵ D₀ →⁷ F₄ transitions of Eu³⁺ ions respectively. The chromaticity coordinates for optimized sample was found to be (0.519, 0.329). Sensitizing with Bi³⁺ ions can affect the luminescence properties of La₂ Zr₂ O₇ :Eu³⁺ phosphors. With reference to the change in Eu³⁺ concentration from x = 1 to 5 at %, color tunable luminescence from blue to orange, red of La₂ Zr₂ O₇ : Bi³⁺ /Eu³⁺ phosphors are observed. The life time decay values, energy level description and CIE chromatic color coordinates for Bi³⁺ , Eu³⁺ in La₂ Zr₂ O₇ : Bi³⁺ /Eu³⁺ co-doped sample was discussed. The spectral overlap between sensitizer, activator ions confirms the efficient energy transfer from Bi³⁺ ions to Eu³⁺ in La₂ Zr₂ O₇ : Bi³⁺ /Eu³⁺ co-doped sample and is via dipole-quadruple mechanism.

Effects of Composition Variations on the Crystalline Phases and Photoluminescence Properties of Ca2+x MgSi2Eu0.025O7+x Phosphors

A solid-state reaction method was used to synthesize Ca_2+x MgSi₂Eu_0.025O_7+x (x = 0-1.0) powders in the air atmosphere and in a reduction atmosphere (95% N₂ + 5% H₂) at 1350 °C and 4 h, and the reduction atmosphere was removed at 800 °C. Only the Ca₂MgSi₂O₇ phase was found in the XRD pattern of the synthesized Ca₂MgSi₂Eu_0.025O₇ powder. The first important discovery was that when the x value of Ca_2+x MgSi₂Eu_0.025O_7+x powders was increased from 0.2 to 0.8, both Ca₂MgSi₂O₇ and Ca₃MgSi₂O₈ phases coexisted in the synthesized Ca_2+x MgSi₂Eu_0.025O_7+x powders, and the diffraction intensity of the Ca₂MgSi₂O₇ (Ca₃MgSi₂O₈) phase decreased (increased) with the x value. The second important discovery was that the Ca₂MgSi₂Eu_0.025O₇ phosphor exhibited stronger photoluminescence excitation (PLE), photoluminescence (PL), and decay curve properties than the Ca_2.2MgSi₂Eu_0.025O_7.2 phosphor, and the Ca₃MgSi₂Eu_0.025O₈ phosphor exhibited stronger PLE, PL, and decay curve properties than the Ca_2+x MgSi₂Eu_0.025O_7+x phosphors for x = 0.4, 0.6, and 0.8. For x = 0.2-0.8, the PL spectra of the Ca_2+x MgSi₂Eu_0.025O_7+x phosphors were a combination of the PL spectra of Ca₂MgSi₂Eu_0.025O₇ and Ca₃MgSi₂Eu_0.025O₈ phosphors. The third important discovery was that as the x value was increased, the maximum emission peak wavelengths of the Ca_2+x MgSi₂Eu_0.025O_7+x phosphors shifted to a lower value, the maximum emission intensity of the PL spectra increased, and the emission light changed from green and cyan to blue.

Eggshell Derived Europium Doped Hydroxyapatite Nanoparticles for Cell Imaging Application

Hen's eggshell, a biological waste product, was turned into a cell imaging probe: europium doped hydroxyapatite (HAp: Eu) nanoparticle using hydrothermal method. Luminescence of the synthesized nanoparticle was studied for various doping concentrations of the lanthanide ion europium (Eu³⁺). Eu doped HAp showed a hexagonal crystal structure and rod-shaped morphology. Well-defined emission peaks of europium, corresponding to the substitution of Eu³⁺ at the Ca²⁺(I) site of HAp, were confirmed from the samples' photoluminescence (PL) spectra. Good biocompatibility up to 500 μg/mL of the samples indicates their potential applications in bioimaging. Synthesized nanoparticles were internalized and used for in vitro imaging of the PC12 cells without any surface modification. The materials' use as a potential in vivo imaging agent is proposed from the haemolysis study.

Temperature dependent quantum cutting in cubic BaGdF5:Eu3+ nanophosphors

A task-specific ionic liquid (IL) is employed as a structure directing agent for the synthesis of quantum cutting BaGdF₅:Eu³⁺ nanophosphors.

Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations

The dominant intensity of parity-forbidden intra-4f transitions of europium(III) over O → Eu charge-transfer band (CTB) intensity is against common perceptions, yet this trend is observed in many germanate hosts and has not been rationalized so far. In search of a plausible explanation for this unusual trend, present work reports an experimental and theoretical investigations in conjunction on two sibling germanate host, namely, Y₂GeO₅ and Y₂Ge₂O₇ having dopant Eu³⁺ in their respective YO₇ polyhedra. Whereas for Y₂GeO₅:Eu³⁺, the CTB is more intense than the intra-4f transitions in the excitation spectrum, in the case of Y₂Ge₂O₇:Eu³⁺, the relative intensities of CTB and intra-4f transitions are reversed. Comparative structural analysis reveals that Eu³⁺ present in YO₇ of Y₂GeO₅ has a greater number of tetra-coordinated oxygen (O_tetra) and yttrium atom as first and second neighbors, respectively (Eu³⁺-O_tetra-Y³⁺ linkages). Conversely, in Y₂Ge₂O₇ host, the Eu³⁺ ion mostly has tricoordinated oxygen (O_tri) as its nearest neighbor and germanium ions next to O_tri (Eu³⁺-O_tri-Ge⁴⁺ linkage). Theoretical calculations reveal that while Y₂GeO₅:Eu has O_tetra(4Y) dominating at the Fermi level and the 4f state of Eu³⁺ remains inert toward mixing, in Y₂Ge₂O₇:Eu, the Fermi level has major contribution from O_tri(2Y + 1Ge) with significant mixing with 4f states of Eu. The dominant control of Eu³⁺-O_tri-Ge⁴⁺ linkages in geometrical and electronic structure of Y₂Ge₂O₇:Eu owing to the GeO₄ surrounding has been attributed to relative poor intensity of O → Eu CTB. Siege of Eu³⁺ by GeO₄ and subsequent occurrence of Eu³⁺-O_tri-Ge⁴⁺ linkages play a dual role: First, it induces electronic rigidity to hinder excitation of electron at bridging (O_tri) oxygen by highly charged small Ge⁴⁺ cation; second, the covalent character in Eu-O bond is achieved by intermixing of Eu's 4f and O_tri 2p orbital which facilitates relaxing of the parity-selection rule thus enhancing the probability of intra-4f transitions. The inferences drawn remain valid when extrapolated to other inorganic oxides having EuO_x polyhedra surrounded by covalent units like PO₄, SiO₄, etc. and have a prevailing number of low-coordinated oxygen atoms and highly charged small cation in the first and second coordination shells, respectively. The optical basicity concept is also found to endorse our explanation. These remarkable generic inferences will pave the rational way for designing efficient phosphors for solid-state lighting.

Optimization of Eu3+ Luminescence in DMSO as a Multiparameter Method for Trace Water Detection

Photoluminescence of Eu3+ in DMSO is intense and ultrasensitive to water, thereby providing a novel method for water detection. Herein, for the first time, we investigated the effects of Eu3+ concentration on luminescence and developed a multiparameter method for trace water detection based on a single luminescence agent. To further extend its practical applications, we explored its performance for water detection in ethanol and gasoline. Our findings demonstrate that it is a sensitive and reliable probe for the detection of a wide concentration range of water in ethanol (0-24.24%) and gasoline (0-32.43%), making Eu-DMSO a promising candidate to detect water in a wide concentration range. These phenomena not only make Eu-DMSO a sensitive agent for in situ water detection in real time but also provide scientifically interesting mechanisms behind its application as a water sensing probe.

Enhancement of Eu3+ Emission in YVO4:Eu3+ Nanocrystals by Li+ Codoping: An Oxidant-Resistant Dispersion and Polymer Film

The enhancement of red emission of YVO₄:Eu³⁺ nanocrystals by Li⁺ codoping has been achieved. The effect of Li⁺ codoping on the crystalline properties and the luminescence of Eu³⁺ has been thoroughly studied. An increase of the unit cell volume and crystallinity of the nanocrystals is observed as the concentration of Li⁺ codoping increases. The lattice expansion could be related to occupation of the interstitial sites by the Li⁺ ions. The nanocrystals appear to be assemblies of rodlike nanostructures along with cube-shaped rough nanostructures of uniform size. The optimum concentration of Li⁺ codoping for luminescence enhancement is found to be 5 at. % at which Eu³⁺ emission is increased by about 2.5 times. The fall in Eu³⁺ emission after codoping of Li⁺ (7-15 at. %) is observed. Is it the increased crystallinity (i.e., the size) or the lattice expansion that poses a limit to luminescence enhancement? Annealing at 500 and 850 °C increased the luminescence emission by threefold and fivefold, respectively. The samples are readily dispersible in deionized water and incorporated easily in the flexible polymer film made of polyvinylidene fluoride. The dispersion-in-water shows bright red luminescence as low as 50 μg/mL. The emission intensity of the dispersion decreases linearly with concentration with a slope almost equal to unity. The dispersion and the flexible film do not show luminescence degradation under the influence of oxidizing H₂O₂ medium. The oxidant-resistant nature with enhanced luminescence could serve as a suitable red emitter for lighting and display applications.

Synthesis and Rational design of Europium and Lithium Doped Sodium Zinc Molybdate with Red Emission for Optical Imaging

Highly efficient fluorescent and biocompatible europium doped sodium zinc molybdate (NZMOE) nanoprobes were successfully synthesized via Polyol method. Non-radiative defect centres get reduced with Li+ co-doping in NZMOE nanoprobes. XRD spectra and Rietveld refinement confirmed successful incorporation of lithium ion and crystallinity was also improved with Li+ co-doping. The shape of phosphor is rod shaped, as determined by TEM. Significant enhancement in photoluminescence intensity was observed with 266, 395 and 465 nm excitations. Profound red emission was recorded for 5 at% Li+ co-doped NZMOE nanoprobes with 266 nm excitation. It shows high asymmetry ratio (~15), color purity (94.90%) and good quantum efficiency (~70%). Judd Ofelt parameters have been calculated to measure intensity parameters and radiative transition rates. In order to measure biocompatibility of the nanoprobes, cytotoxicity assays were performed with HePG2 cells. The fluorescence emitted from phosphor material treated HePG2 cells was also measured by Laser Scanning Confocal Microscopy. The bright red fluorescence in HePG2 cells treated with very low concentration (20 μg/ml) of phosphor material indicates that it could be a promising phosphor for biological detection or bio-imaging.

Luminescent enhancement study of 3Tb,5Ce,5Li:CaF2: effect of Li+ ion concentration and hyperthermia applications of 3Tb:CaF2/Fe3O4 nanocomposite

Codoping of Li⁺ ions in luminescent CaF₂:3Tb:5Ce nanoparticles more than doubled its intensity.

Correlating Structure and Luminescence Properties of Undoped and Eu3+-Doped La2Hf2O7 Nanoparticles Prepared with Different Coprecipitating pH Values through Experimental and Theoretical Studies

Understanding the structure-property relationship and optimizing properties of phosphors for use in lighting and scintillation fields is an important materials challenge. In this work, we investigated the effects of the pH value of the coprecipitating solution adjusted by the concentration of NH₄OH(aq) on the structure and optical properties of the obtained La₂Hf₂O₇ nanoparticles (NPs). The obtained NPs stabilize in the ideal pyrochlore structure, but the extent of ordering increased with an increase in the pH value used. The NPs prepared at pH = 12.1 displayed the best optical performance owing to the balance of the crystallinity, agglomeration, and surface defects. On the basis of density functional theory (DFT) calculations, the origin of violet-blue emission in undoped La₂Hf₂O₇ NPs was attributed to defect states in the electronic band gap arising due to oxygen defects. For the La₂Hf₂O₇:Eu³⁺ NPs, the Eu³⁺ dopants possess low symmetry and their occupancy is more favorable at the LaO₈ site. DFT calculations further justify the complete host-to-dopant energy transfer and origin of the most intense red emission observed experimentally. Understanding the interplay of the experimental and theoretical results thus is a very useful general approach for improving the efficiency of luminescent materials.

Exploration into the Syntheses of Gallium- and Indiumborates under Extreme Conditions: M5 B12 O25 (OH): Structure, Luminescence, and Surprising Photocatalytic Properties

Explorative solid-state chemistry led to the discovery of the two new compounds Ga₅ B₁₂ O₂₅ (OH) and In₅ B₁₂ O₂₅ (OH). Extreme synthetic conditions within the range of 12 GPa and a temperature of 1450 °C realized in a Walker-type multianvil apparatus resulted in the formation of an unprecedented tetragonal structure with the exclusive presence of condensed BO₄ tetrahedra, forming cuboctahedral cavities. Doping of these cavities with Eu³⁺ in In₅ B₁₂ O₂₅ (OH) yielded in an orange-red luminescence. Photocatalytic tests of In₅ B₁₂ O₂₅ (OH) revealed a hydrogen production rate comparable to TiO₂ but completely co-catalyst free.

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.

Lu3+ doping induced photoluminescence enhancement in novel high-efficiency Ba3Eu(BO3)3 red phosphors for near-UV-excited warm-white LEDs

Novel high-efficiency Ba₃Eu(BO₃)₃:Lu³⁺ red phosphors with internal quantum efficiency as great as 87% were developed for near-UV-excited warm-white LEDs.

On peculiarities of Eu3+ and Eu2+ luminescence in Sr2GeO4 host

Powders of Sr₂GeO₄:Eu were prepared in air or forming gas and were investigated for their luminescent properties in the 20–300 K range of temperatures, and as much as eight emitting sites of Eu³⁺ and just one of Eu²⁺ were found.

Synthesis, crystal structure, and luminescence properties of a new europium silicate

A new europium silicate, NaEuSi₃O₇(OH)₂ (denoted as 1), was synthesized under high-temperature and high-pressure conditions, and structurally characterized by single-crystal and powder X-ray diffraction (XRD) analyses.

Excitation of magnetic dipole transitions at optical frequencies

We use the magnetic field distribution of an azimuthally polarized focused laser beam to excite a magnetic dipole transition in Eu^{3+} ions embedded in a Y2O3 nanoparticle. The absence of the electric field at the focus of an azimuthally polarized beam allows us to unambiguously demonstrate that the nanoparticle is excited by the magnetic dipole transition near 527.5 nm. When the laser wavelength is resonant with the magnetic dipole transition, the nanoparticle maps the local magnetic field distribution, whereas when the laser wavelength is resonant with an electric dipole transition, the nanoparticle is sensitive to the local electric field. Hence, by tuning the excitation wavelength, we can selectively excite magnetic or electric dipole transitions through optical fields.

Roles of solvent, annealing and Bi3+ co-doping on the crystal structure and luminescence properties of YPO4:Eu3+ nanoparticles

There are roles of solvent, annealing and Bi³⁺ co-doping on crystal structure and luminescence properties of YPO₄:Eu³⁺ nanoparticles.