Photoluminescence and electrochemical performance evaluation of Eu3+ doped MgAl2O4 phosphors for LED and energy storage applications

Crystal structure of Eu³⁺ doped MgAl₂O₄ (MAO) phosphors synthesised by solid state reaction method was investigated using X-ray diffraction. Raman peaks appeared at 307 cm^?1, 408 cm^?1, 668 cm^?1 and 767 cm^?1 were assigned to F_2g (1), F_2g (2), E_g and A_1g respectively. Spherical morphology and microstructural analysis of synthesised phosphors was analysed by Field emission scanning electron microscope (FESEM) high resolution transmission electron microscope (HRTEM) and energy dispersive X-ray analysis (EDAX) was used to establish the chemical composition of the phosphors. Optical properties were analysed by photoexcitation (394 nm) and photoluminescence (PL) spectra displayed all the characteristic emission of Eu³⁺ related to transition ⁵D₀ to ⁷F_j (j = 0, 1, 2, 3, 4). The emission color was observed in red region and it was confirmed by the Commission Internationale de l’Eclairage (CIE) chromatic coordinate graph. The color purity and quality (correlated color temperature- CCT value) of red light was observed in 0.9% Eu³⁺ doped MAO to be 90.76% and 2097K respectively. Electrochemical evaluation of Eu³⁺ doped MAO was performed through cyclic voltammetry (CV) studies.     

Photoluminescence properties of Ce3+/Mn2+ doped calcium zirconium silicate phosphors with energy transfer for white LEDs

A series of Ce³⁺ doped and Ce³⁺/Mn²⁺ co-doped calcium zirconium silicate CaZrSi₂O₇ (CZS) phosphors have been synthesized via conventional high temperature solid state reactions. The luminescence properties, energy transfer between Ce³⁺ and Mn²⁺ have been investigated systematically. Under 320 nm excitation, the phosphor CZS: 0.05Ce³⁺ exhibit strong blue emission ranging from 330 nm to 500 nm, attributed to the spin-allowed 5d-4f transitions of Ce³⁺ ions. There are two different emission centers of Ce³⁺ ions, Ce³⁺(I) and Ce³⁺(II). The emission spectra of Ce³⁺, Mn²⁺ co-doped phosphors shows a broad emission around 550 nm corresponding to the ⁴T₁(⁴G)-⁶A₁(⁶S) spin-forbidden transition of Mn²⁺. The energy transfer between Ce³⁺ and Mn²⁺ is detected and the transfer efficiency of Ce³⁺(II) to Mn²⁺ is faster than that of Ce³⁺(I) to Mn²⁺. The resonant type is identified via dipole-dipole mechanism. Additionally, a blue-shift emission of Ce³⁺ and a red-shift emission of Mn²⁺ have been observed following the increase of Mn²⁺ content in relation to the energy transfer. Thermal quenching has been investigated and the emission spectra show a blue-shift with the temperature increases, which have been discussed in details. CZS: 0.05Ce³⁺, yMn²⁺ phosphors can be tuned from blue to white and even to yellow by adjusting the Mn²⁺ content. All the results indicate that CZS: Ce³⁺, Mn²⁺ phosphor have a potential application for near-UV LEDs.     

Tunable white light and energy transfer of Eu2+-Tb3+-Eu3+ tri-activated glasses synthesized in air

An ever increasing demand for white light-emitting diodes (W-LEDs) results in the gradual growth of research on functionalized luminescent glasses. In this paper, single-composition tunable white-emitting Eu²⁺-Tb³⁺-Eu³⁺ tri-activated glasses were synthesized by melt quenching method without additional reducing atmosphere. The coexistence of Eu²⁺ and Eu³⁺ was confirmed by ultraviolet-visible transmission spectra, photoluminescent spectra, fluorescence decay curves, and X-ray photoelectron spectroscopy. Tb³⁺ can act as bridge to connect Eu²⁺-Eu³⁺ luminescent centers by energy transfer. Tone-tunable white light can be achieved by coupling the emission centered at 412, 541, and 612 nm contributed from Eu²⁺, Tb³⁺, and Eu³⁺, respectively. By adjusting the relative content of Eu²⁺/Tb³⁺/Eu³⁺, ideal chromaticity coordinates of (0.33, 0.33) can be achieved under excitation of ultraviolet light. High thermal stability and tiny chromaticity shift were exhibited in samples. These results suggest that Eu²⁺-Tb³⁺-Eu³⁺ tri-activated glasses have great potential application in ultraviolet-driven W-LEDs.     

Near white light emission from K+ ion compensated CaSO4:Dy3+,Eu3+ phosphors

Dy³⁺:Eu³⁺ doped calcium sulfate (CaSO₄:Dy³⁺,Eu³⁺) phosphors co-doped with various K⁺ compensator concentrations were synthesized by recrystallization method. These orthorhombic phased phosphors showed intense multi-color near white light. The multi-color aspect ratios and the emission life times were strongly dependent on K⁺-concentration. These results suggest that the rare-earth (Re³⁺) ions are situated at the sites of Ca²⁺ and the site occupancy was being compensated by K⁺ ions. The near white light emission and large lifetimes suggest that present phosphor could be potentially applied as a blue excited white light-emitting phosphor for light emitting diodes.     

Eu2+, Dy3+: Sr2B5O9Cl,a new blue-emitting phosphor with long persistence

A new Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphor with long persistence was synthesized in a reducing atmosphere by a solid-state reaction process. The pure-phase phosphor was obtained by calcination at 900 °C. The introduction of Eu²⁺ into the lattice of the matrix resulted in a broad blue emission centered at 423 nm, which was due to the characteristic 4f6⁵d¹ to 4f⁷ energy transfer of Eu²⁺ ions. Both Eu-doped and Dy/Eu-codoped phosphors displayed afterglow behaviors due to the electron traps generated by the incorporation of tri-valanced rare earth cations into the original Sr lattice sites. The afterglow of Eu²⁺: Sr₂B₅O₉Cl and Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphors showed standard double exponential decay behaviors, and the Eu²⁺/Dy³⁺ co-doped sample demonstrated better afterglow properties than Eu²⁺-doped one. A longer lifetime for the electrons was confirmed after the afterglow decay curve simulation. Based on the analysis of thermally stimulated luminescence (TSL), the difference in afterglow was attributed to the different trap concentrations induced by the Dy³⁺ (Eu³⁺) doping in the Sr₂B₅O₉Cl matrix.     

Tunable luminescence and energy transfer properties of MgY4Si3O13: Ce3+, Tb3+, Eu3+ phosphors

The tricolor-emitting MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors for ultraviolet-LED have been prepared via a high-temperature solid-state method. X-ray diffraction, photoluminescence emission, excitation spectra and fluorescence lifetime were utilized to characterize the structure and the properties of synthesized samples. Two different lattice sites for Ce³⁺ are occupied from the host structure and the normalized PL and PLE spectra. The emissions of single-doped Ce³⁺/Tb³⁺/Eu³⁺ are located in blue, green and red region, respectively. The energy transfer from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ has been validated by spectra and decay curves and the energy transfer mode from Tb³⁺ to Eu³⁺ was calculated to be electric dipole-dipole interactions. By adjusting the content of Tb³⁺ and Eu³⁺ in MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺, the CIE coordinates can be changed from blue to green and eventually generate white light under UV excitation. All the results indicate that the MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors are potential candidates in the application of UV-WLEDs.     

Tunable single-phased white-emitting Sr3Y(PO4)3:Dy3+ phosphors for near-ultraviolet white light-emitting diodes

Single-component white-emitting Sr₃Y(PO₄)₃:Dy³⁺ phosphors were synthesized by a high-energy deformation process. X-ray diffraction patterns showed the resulting crystallized phase to be of cubic structure, space group I-43d (no. 220). The broad-band excitation spectra between 250 and 500 nm were observed by monitoring the emission wavelength at 576 nm, which matches well with commercial near-UV or blue LED chips. Under a 352 nm excitation, the emission peaks were observed at 483 nm (blue), 576 nm (yellow), and 666 nm (red), corresponding to the ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, and ⁴F_9/2 → ⁶H_11/2 transitions of Dy³⁺ ions. The optimized doping concentration of Dy³⁺ ion was 8 mol%. By controlling the Dy³⁺ ion concentration, tunable colors from white to yellow were obtained in Sr₃Y(PO₄)₃:Dy³⁺ phosphors. These results reveal that studied materials may be a promising candidate for white LED applications.     

Improved photoluminescence,thermal stability and temperature sensing performances of K+ incorporated perovskite BaTiO3:Eu3+ red emitting phosphors

K⁺ ions incorporated perovskite Ba_(1−x)TiO₃:x Eu³⁺ red emitting phosphors synthesized via facile solid -state reaction method has been investigated in the current study. The photoluminescence and decay time behavior of Ba_(1−x−y)TiO₃:x Eu³⁺,yK⁺ phosphors are investigated as a function of Eu³⁺, K⁺ concentration and temperature. An intense and sharp emission peak at 615 nm was exhibited by the phosphors upon excitation at 397 nm (⁷F₀→⁵L₆). It can be credited to the hypersensitive electric dipole transition ⁵D₀→⁷F₂, which confirms that Eu³⁺ ions are located at non-centrosymmetric site of the host. The incorporation of K⁺ ions in optimized Ba_0.95TiO₃:0.05 Eu³⁺ phosphor resulted in a remarkable enhancement of photoluminescence intensity by 2.33 times as compared to bare one. The Ba_0.89TiO₃:0.05 Eu³⁺, 0.06 K⁺ phosphors were found to observe good temperature sensing along with adequate thermal stability even at 427 K. Furthermore, the photometric parameters have been also studied which are strongly facilitate the prepared ceramic samples as suitable for potential application in lighting.     

Plant habitat-conscious phosphors: Tuneable luminescence properties of Dy3+-doped Ca8ZnY(PO4)7 phosphors by co-dopants Mg2+ and B3+

Outdoor lighting and other lighting systems can disrupt natural plant growth habits. Thus, LED lighting that is not detrimental to plant growth is required. In our study, Dy³⁺-doped Ca₈ZnY(PO₄)₇:Dy³⁺ phosphor with enhanced luminescence properties caused by the co-dopants Mg²⁺ and B³⁺ were synthesised. The samples had multiple excitation peaks, indicating they are excited by either near-ultraviolet (n-UV) or blue chips. All samples exhibited bright narrow yellow and blue emission corresponding to the transitions of Dy³⁺ ions with ⁴F_9/2→⁶H_13/2 and ⁴F_9/2→⁶H_13/2, respectively. Moreover, doping with Mg²⁺ and B³⁺ enhanced the luminescence intensity, reaching 113.6 and 119.7%, respectively. In addition, the luminescence emission intensity at 150 °C was maintained at approximately 95% of the initial value at 25 °C, and its thermal stability increased by 123%. Devices assembled with an n-UV chip (388 nm) and the as-obtained CZMYP:Dy³⁺ phosphor emitted a bright warm white light and simulated outdoor dark lighting for tobacco cultivation, indicating that the as-prepared phosphor is an excellent candidate material for plant habitat-conscious phosphors.     

Synthesis and luminescence studies of Dy3+ doped Li3Sc(BO3)2 polycrystalline powder for warm white light

Li₃Sc(BO₃)₂, an orthoborate polycrystalline compound, was synthesised using the solid-state synthesis method as a pure and Dy₂O₃-doped material. Dy³⁺ ions were used in various concentrations (from 1 to 6 mol. %). The experimental powder X-ray diffraction data and calculated Rietveld refined data are found to be in good agreement, verifying the effectiveness of the synthesis procedure. The luminescence studies were performed under the excitations of X-ray, proton beam, and UV light. The success of radioluminescence studies verifies the prospects of the Dy³⁺-doped compound for its application as a radiation scintillator in imaging. The experimental study of cross-relaxation processes confirms the lack of potential evidence of the quenching of the emission peak at 765 nm through the absorption via ⁶H_15/2 → ⁶F_3/2 electronic transition cross-relaxation channel ?1. The CIE 1931 colour coordinates and correlated colour temperatures were determined for all doped samples under X-ray, proton beam, and photoluminescence excitations. The obtained combined emission colour appeared in the warm white region, unlike many other Dy³⁺-doped phosphors that suffer suppression of luminescence through the cross-relaxation process.     

Laser synthesis and luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

A laser melting method has been developed for the synthesis of highly luminescent, long-lasting SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors. The high temperature achieved in high-power density CO₂ laser irradiation of mixtures of SrCO₃, Al₂O₃, Eu₂O₃, and Dy₂O₃ enabled the one-step, fast synthesis of these phosphors in air at atmospheric pressure. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy characterization studies reveal that the produced materials consist of monoclinic SrAl₂O₄ grains extensively surrounded by rare-earth ion-enriched grain boundaries. The photoluminescence properties of laser-produced SrAl₂O₄:Eu²⁺, Dy³⁺ materials are discussed. The results reported here suggest that this laser melting method is a promising route for the synthesis of ceramic phosphors. It is presented as an alternative to the conventional sol–gel and solid-state methods, which require the use of high-temperature furnaces, flux additives, and reducing atmospheres.     

Energy transfer and color-tunable emission in Ba2Y2Si4O13:Bi3+,Eu3+ phosphors

Single-composition Ba₂Y₂Si₄O₁₃:Bi³⁺,Eu³⁺ (BYSO:Bi³⁺,Eu³⁺) phosphors with color-tunable and white emission were prepared by conventional high temperature solid-state reaction method. The structural and luminescent properties of these phosphors were thoroughly investigated through X-ray diffraction, photoluminescence, and decay curves. BYSO:Bi³⁺ phosphors show two excitation peaks at 342 and 373 nm, and give two emission peaks at 414 and 503 nm, respectively, indicating that there are two sites of Bi³⁺ in BYSO. The energy transfer from Bi³⁺ to Eu³⁺ was investigated in detail. Varied hues from blue (chromaticity coordinate [0.219, 0.350]) to white (0.288, 0.350) and orange-red light (0.644, 0.341) can be generated by adjusting the content of Eu³⁺. Pure white light emission (0.311, 0.338) can be obtained under the excitation of 355 nm in BYSO:3%Bi³⁺,20%Eu³⁺ phosphor. Besides, BYSO:Bi³⁺,Eu³⁺ phosphors exhibit distinct thermal quenching properties, whose emission intensity at 473 K is 82.6% of that at 298 K. Our results indicate that BYSO:Bi³⁺,Eu³⁺ may be applied as conversion phosphors for n-UV-based W-LEDs.     

Molten salt synthesis and optical properties of Eu3+, Dy3+or Nd3+ doped NiNb2O6 columbite-type phosphors

Pure, Eu³⁺, Dy³⁺ or Nd³⁺-doped NiNb₂O₆ powders have been prepared by a molten salt synthesis method by using Li₂SO₄–Na₂SO₄ salt mixture as a flux at relatively low temperatures as compared to the solid state reaction method. X-ray diffraction patterns of pure NiNb₂O₆ samples indicated an orthorhombic single phase. For Eu³⁺-doped NiNb₂O₆ samples, the luminescence of Eu³⁺ was observed at 615 nm as red emission while Dy³⁺-doped NiNb₂O₆ showed yellow emission at 577 nm and Nd³⁺ doped sample exhibited a typical emission at 1064 nm varying with the Eu³⁺ or Nd³⁺ doping concentrations. These luminescence characteristics of the doped samples may be attributed to the energy transfer between rare earth ions and NiO₆ octahedral groups in the columbite structure.     

Mechanism of long afterglow in SrAl2O4:Eu phosphors

Phosphors of SrAl₂O₄:Eu (SAO), B-doped (SBO), and B, F co-doped (SFO) were prepared by a high-temperature solid-state reaction method. The phosphors emit intense green light under UV excitation. SBO displayed significantly enhanced long afterglow. The decay time of SBO was 20 times bigger than that of SAO, while that of SFO was only 16% of that of SBO. The results suggest that B doping favors the formation of oxygen vacancies due to the unique bonding property of B. At the same time, B, F co-doping has the opposite effect, ascribed to the presence of F. The related partial density of state and the orbital structures were calculated using the first-principles density functional theory (DFT). The orbital structure of SBO showed that high partial density states are localized around the O vacancies, which can trap excited electrons, leading to improved long-afterglow luminescence.     

Near-infrared photo-responsive Er3+-K+ co-doped Y2O3 phosphors with enhanced UC luminescence

Y₂O₃: x% Er³⁺ (x=5, 7, 10, 12, 15) and Y₂O₃: 10% Er³⁺,x% K⁺ (x=0, 1, 3, 5, 7, 10, 15) phosphors were successfully prepared by a low-temperature combustion method. The structure as well as the absorption/emission spectra of phosphors were investigated. The effect of doping concentration of K⁺ ions on the upconversion (UC) luminescence of Y₂O₃: 10% Er³⁺ phosphor was examined and the possible optical transitions were discussed. The results showed that K⁺ ion doping not only changed the microstructure and crystallinity of the phosphors, but also enhanced its UC luminescence intensity. The Y₂O₃: 10% Er³⁺, 7% K⁺ phosphor exhibit the strongest UC emission intensity. Compared with the Y₂O₃: 10% Er³⁺ phosphor, the UC luminescence intensity at 563 nm and 661 nm was enhanced by 67.8 and 27.3 times for the K-codoped samples, respectively. The phosphor with the optimal doping concentration was mixed with a polymer to form a composite film, which was employed for the fabrication of near-infrared (NIR) photo-responsive detection devices. The device exhibited strong photo-current response to NIR light at 980 nm, implying that our work could inspire new design strategy for the development of NIR photo-detection devices.     

Preparation and luminescence of SrAl2O4: Eu2+,Dy3+ phosphors coated with maleic anhydride

In this paper, maleic anhydride is directly coated on the surface of SrAl₂O₄: Eu²⁺, Dy³⁺ (SAO‐ED) phosphors by an interfacial coordination chemistry method. Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectra (XPS), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) methods are used to characterize the coating. The experimental result shows that a dense coating layer is consisting of maleic anhydride coordination with metal ions on the surface of the phosphors and the coating process does not destroy the crystal structure of the phosphors. It is also found that the introduction of maleic anhydride does not change the excitation and emission spectra of SAO‐ED phosphors, but decreases the luminous intensity, which is verified by the photoluminescence (PL) measurement. Afterglow delay curves show that the initial brightness of coated SAO‐ED phosphors decreases, but the afterglow decay rate of coated phosphors is slower than that of uncoated phosphors after they both are immersed into water for one month. This indicates that the coating layer protects the phosphors and the crystal structure of coated phosphors in water was not destroyed.     

Sr3GdLi(PO4)3F:Eu2+, Mn2+: A tunable blue-white color emitting phosphor via energy transfer for near-UV white LEDs

A series of Eu²⁺ and Mn²⁺ co-doping Sr₃GdLi(PO₄)₃F phosphors have been synthesized through high temperature solid state reaction. Eu²⁺ single doped Sr₃GdLi(PO₄)₃F phosphors have an efficient excitation in the range of 230–430 nm, which is in good agreement with the commercial near-ultraviolet (n-UV) LED chips, and gives intense blue emission centering at 445 nm. The critical distance of the Eu²⁺ ions in Sr₃GdLi(PO₄)₃F is computed and demonstrated that the concentration quenching mechanism of Eu²⁺ is mostly caused by the dipole-dipole interaction. By co-doping Eu²⁺ and Mn²⁺ ions in the Sr₃GdLi(PO₄)₃F host, the energy transfer from Eu²⁺ to Mn²⁺ that can be discovered. With the increase of Mn²⁺ content, emission color can be adjusted from blue to white under excitation of 380 nm, corresponding to chromatic coordinates change from (0.189, 0.108) to (0.319, 0.277). The energy transfer from Eu²⁺ to Mn²⁺ ions is proven to be a dipole-dipole mechanism on the basis of the experimental results and analysis of photoluminescence spectra and decay curves. This study infers that the obtained Sr₃GdLi(PO₄)₃F:Eu²⁺, Mn²⁺ phosphors may be a potential candidate for n-UV LEDs.     

Energy transfer and luminescence study of Dy3+ doped zinc-aluminoborosilicate glasses for white light emission

A series of Dy³⁺ doped aluminoborosilicate glasses with general formula 20SiO₂-(40-x) B₂O₃–10Al₂O₃–20NaF₂–10ZnO-xDy₂O₃ (x = 0, 0.1, 0.5, 1.0. 1.5, 2.0 and 2.5 mol %) were prepared by melt-quenching method. The FTIR analysis confirms the presence of stretching and bending vibrations of BO₄, BO₃ and SiO₄ units in the prepared glasses. DTA results show that Tg is decreasing with addition of Dy³⁺ ions in the glass system. Theoretically calculated mechanical properties such as elastic modulus, bulk modulus, shear modulus and Poisson's ratio suggest the increase in mechanical stability of glasses with dysprosium addition. Also experimental analysis carried out using Vicker's microhardness suggests glass stability with applied loads. Absorption spectrum shows twelve bands that exist due to transition from ⁶H_15/2 level to different excited levels. Nephelauxetic ratio and bonding parameter calculated shows decreasing ionicity of glasses with increase in Dy³⁺ ions. Judd-Oflet parameter calculated for all the glasses follow the trend Ω₆ > Ω₄ > Ω₄. Luminescence study shows three emission peaks having transitions from ⁴F_9/2 → ⁶H_15/2 (blue), ⁴F_9/2 → ⁶H_13/2 (yellow) and ⁴F_9/2 → ⁶H_11/2 (red). Radiative parameters calculated suggest higher stimulated emission cross-section for present glasses having ⁴F_9/2 → ⁶H_13/2 transition. The decay measurement for all the glass samples were recorded with an excitation at 350 nm and monitoring emission at 575 nm corresponding to the ⁴F_9/2 → ⁶H_13/2 transition and decay curves were fitted to bi-exponential fit. The CIE colour chromaticity coordinates were determined using CIE chromaticity diagram and the values were found to be in close proximity with the standard white light (0.33. 0.33) for all the glasses. Further colour correlated temperature values were found to lie in the near bright white region with CCT around ~4000 K.     

Energy transfer and multicolor tunable emission in single-phase Tb3+, Eu3+ co-doped Sr3La(PO4)3 phosphors

A series of green-to-red color-tunable Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors were prepared by high temperature solid-state method. The crystal structures, photoluminescence properties, fluorescence lifetimes, and energy transfer of Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ were systematically investigated in detail. The obtained phosphors show both a green emission from Tb³⁺ and a red emission from Eu³⁺ with considerable intensity under ultraviolet (UV) excitation (~377 nm). The emission colors of the phosphors can be tuned from green (0.304, 0.589) through yellow (0.401, 0.505) and eventually to red (0.557, 0.392) due to efficient Tb³⁺-Eu³⁺ energy transfer (ET). The Tb³⁺→Eu³⁺ energy transfer process was demonstrated to be quadrupole-quadrupole mechanism by Inokuti-Hirayama model, with maximum ET efficiency of 86.3%. The results indicate that the Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors might find potential applications in the field of lighting and displays.     

Color-tunable properties of Eu3+- and Dy3+-codoped Y2O3 phosphor particles

Rare-earth phosphors are commonly used in display panels, security printing, and fluorescent lamps, and have potential applications in lasers and bioimaging. In the present study, Eu³⁺- and Dy³⁺-codoped uniform-shaped Y₂O₃ submicron particles were prepared using the urea homogeneous precipitation method. The structure and morphology of the resulting particles were characterized by X-ray diffraction, field emission scanning electron microscope, and field emission transmission electron microscope, whereas their optical properties were monitored by photoluminescence spectroscopy. The room-temperature luminescence color emission of the synthesized particles can be tuned from red to yellow by switching the excitation wavelength from 254 to 350 nm. The luminescence intensities of red and yellow emissions could be altered by varying the dopant concentration. Strong quenching was observed at high Eu³⁺ and Dy³⁺ concentrations in the Y₂O₃ host lattice.