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In most inorganic phosphors, increasing the concentration of activators inevitably causes the concentration quenching effect, resulting in reduced emission intensity at a high level of activator doping and the conventional practice is to limit the activator concentration to avoid the quenching. In contrast, SiAlON ceramics preserve their chemical composition over a very wide range of doping of activator ions, which favors the adjustment and optimization of the luminescence properties avoiding concentration quenching. Here, we investigate the photoluminescence properties of Ho-doped SiAlON (Ho-SiAlON) ceramics phosphors prepared by the hot-press method. Ho-SiAlON ceramics show strong green visible (554 nm) as well as infrared (2046 nm) broadband downshifting emissions under 348 nm excitation. It is shown that there is no concentration quenching, even at a very high level of Ho doping. The emission intensity of the 554 nm band increased two-fold when the Ho concentration is doubled. The results show that the Ho-SiAlON ceramics can be useful for efficient green phosphors. [ABSTRACT FROM AUTHOR]

A new red‐emitting Eu3+ (1−17 mol%)‐doped Na3Mg4LiSi12O30 (NMLS) phosphor was prepared using a conventional solid‐state reaction method at low temperature. The prepared samples belong to a hexagonal structure with a good match to JCPDS card no. 73–0934. The photoluminescence (PL) emission spectrum showed an intense peak at 612 nm when excited at 393 nm. The variation of electric dipole transition (5D0–7F2) emission intensity with increasing Eu3+ ion concentration was investigated. The concentration quenching at 11 mol% is due to the dipole–dipole interaction mechanism in the NMLS host. The optimized NMLS:Eu3+phosphor shows 2.18 times higher luminescence intensity than the (Y,Gd)BO3 (YGB) commercial phosphor. The NMLS:Eu3+showed an intense red emission, having Commission Internationale de l'éclairage (CIE) coordinates (0.6280, 0.3691) and colour purity of 99.2%. The resulting phosphor exhibits good thermal stability of 80% at 423 K. The magnified images of fingerprint showed various minute features such as bridges, sweat pores, ridge end, bifurcation, island and core with better visualization under 393 nm excitation. Furthermore, the optimized NMLS:Eu3+ was used for pc‐LED, latent fingerprints, and anticounterfeit applications as a promising red phosphor. [ABSTRACT FROM AUTHOR]

High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%–98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%–40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ∼9% and ∼25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ∼9% (20% Yb3+) to ∼7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ∼7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials. [ABSTRACT FROM AUTHOR]

We have grown arrays of silver nanowires in pores of anodic alumina membranes (metamaterials with hyperbolic dispersion at λ ≥ 615 nm), spin coated them with the dye-doped polymer (HITC:PMMA), and studied the rates of radiative and nonradiative relaxation as well as the concentration quenching (Förster energy transfer to acceptors). The results were compared to those obtained on top of planar Ag films and glass (control samples). The strong spatial inhomogeneity of emission kinetics recorded in different spots across the sample and strong inhibition of the concentration quenching in arrays of Ag nanowires are among the most significant findings of this study.

The technique of introduction a fluorescent dye Tris(bipyridine)ruthenium (II) chloride into nanoparticles of silicon dioxide in isopropyl alcohol was tested. The preparation of nanoparticles was carried out by means of the Stober method. The optimal reaction conditions were determined. It was found out that the penetration of a dye into silicon dioxide nanoparticles reduced the effect of concentration quenching of the dye and made it possible to achieve an increase in fluorescence intensity in the solution more than twofold. An attempt was made to functionalize the obtained particles by introducing amino groups onto the particle surface. Fused silver nanoparticles were seeded with silver nanoparticles.

Eu3+ and/or Sm3+‐doped CaMoO4 phosphors were prepared using a hydrothermal method. The X‐ray diffraction (XRD) results show that the sample is in a tetragonal CaMoO4 phase, the space group is I41/a (88), the lattice constants are a = b = 5.226 Å, c = 11.430 Å, and V = 312.2 Å3. We explored the effects of Eu3+ doping concentration, reaction temperature, preparation time, and the energy transfer relationship between Eu3+ and Sm3+ on the phosphors. The Commission Internationale de l'éclairage (CIE) calculation results indicated that under excitation by ultraviolet light at 283 nm, the CIE coordinates of some CaMoO4:Eu3+/Sm3+ materials are located in the near‐white light region, and could be used as potential candidates for single‐matrix white phosphors. [ABSTRACT FROM AUTHOR]

Novel red phosphors Sr7Sb2O12:Eu3+ and Sr7Sb2O12:Eu3+, M+ (M = Li, Na, K) were synthesized via a high temperature solid-state method and their luminescent properties were investigated to figure out the promising application in warm white light-emitting diodes (LED). The phase structure, crystal morphology, luminescence properties, luminescence decay lifetime, thermal stability and chromaticity coordinate of the as-synthesized phosphors were investigated in detail. Sr7Sb2O12:Eu3+ could be efficiently excited by the near-ultraviolet (UV) light and exhibited bright red emission around 612 nm. When co-doped with the charge compensation M+ (M = Li, Na, K) ions, the emission intensity of Eu3+ can be enhanced to some extent. The optimal Eu3+ doping concentration was determined to be about x = 0.2 and concentration quenching mechanism in Sr7Sb2O12:Eu3+ sample was attributed to the electric dipole–dipole interaction. The temperature-dependent spectra of Sr7Sb2O12:Eu3+ implied that this sample shows good thermal-stable properties. The decay lifetime of Sr7Sb2O12:0.2Eu3+ was about 1.44 ms. Combining with the red Sr7Sb2O12:0.20Eu3+, blue BaMgAl10O17:Eu2+, yellow (Ba,Sr)2SiO4:Eu2+ phosphor and a 395 nm near-UV LED chip, a white LED with low correlated color temperature (CCT = 4260 K) and high-color rendering index (Ra = 91.8) was fabricated. The overall work suggested that Sr7Sb2O12:Eu3+ phosphor is a promising red-emitting component applied in warm white LED. [ABSTRACT FROM AUTHOR]

We have studied the dependence of concentration quenching of luminescence (donor–acceptor energy transfer) on the thickness d of dye-doped polymeric films (HITC:PMMA) and found its strong inhibition at small values of d. This phenomenon is tentatively explained by a limited number of acceptors, which donors’ excitation can reach in thin samples, if the film’s thickness is comparable to the diffusion length of the energy transfer. The latter mechanism, along with effective reduction of the dye concentration, is responsible for an inhibition of the concentration quenching of dye molecules impregnating porous alumina membranes. The elongation of emission kinetics in thick (≥3 μm) HITC:PMMA films is cautiously attributed to the samples’ crystallinity.

[Display omitted] • Nanophosphors Ca 9 La(PO 4) 7 : Tb3+ were prepared via eco-friendly solution combustion methodology. • The crystallite size has been determined using various techniques. • CIE and CCT demonstrate brilliant green emission. • Concentration quenching and resonant energy relocation process attributed to quadrupole–quadrupole interactions. • Advanced luminescent dynamics calculations related to quantum efficiency. In this investigation, we present cost-effective synthesis and optical studies of Ca 9 La(PO 4) 7 : Tb3+ nanophosphors. XRD study authorized that Ca 9 La(PO 4) 7 : Tb3+ nanophosphors crystallizes in trigonal phase with R3c(1 6 1) space group. The synthesized Ca 9 La(PO 4) 7 : Tb3+ nanophosphors have diameter ranging from 30 to 60 nm, as analyzed via Scherrer's and W-H method along with SEM and TEM studies. The Ca 9 La(PO 4) 7 : Tb3+ phosphors are readily excited by near-UV radiance of 380 nm. EDAX analysis ascertained the homogeneous distribution and highly pure chemical composition of synthesized nanophosphors. The calculated band-gap of Ca 9 La (0.30) (PO 4) 7 : 0.70 Tb3+ optimized nanophosphor estimated via Kubelka-Munk and Tauc's relation is 4.22 eV which validated their application scope in semiconductors. The emission profiles of synthesized nanophosphors depict vivid green luminescence attributed to the transitions 5D 4 → 7F 5 of Tb3+ ions. The photoluminescence intensity of Ca 9 La(PO 4) 7 : Tb3+ rises up to 70 mol% doping of Tb3+ and then declines due to phenomenon of concentration quenching explained via Dexter's and Van Uitert's theoretical model. Decay curve analysis via Auzel's model, established that Ca 9 La(PO 4) 7 : Tb3+ developed nanophosphors manifest exceptional quantum efficiency. Colorimetric features like CIE coordinates and CCT depicted vibrant green hue with cool appearance for synthesized nanophosphors. The Ca 9 La(PO 4) 7 : Tb3+ developed luminescent nanomaterials can be used as bright green emitting component for designing advanced WLEDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimal photoluminescence at 2 wt% Dy3+ doping, enhancing efficiency for LEDs. • Dy3+-doped LMBO phosphors show thermal stability and lifetime suited for LED use. • Identified quenching mechanisms; photoluminescence decreases with temperature. • Calculated critical quenching distance (R c) for Dy3+ in LMBO as 24.66 Å. • Correlated color temperature of 6595 K at 2 wt% Dy3+, producing cool white light. Despite significant advancements in borate-based phosphors, improving luminescent efficiency and thermal stability, particularly at high temperatures, remains a persistent challenge. In this study, Dy3+-doped LaMgB 5 O 10 (LMBO) phosphors were synthesized and characterized for their photoluminescent properties to address these issues. Under 344 nm excitation, the Dy3+-activated LMBO phosphors exhibited strong luminescence with characteristic peaks at 482 nm (blue), 578 nm (yellow), and 663 nm (red), corresponding to specific Dy3+ transitions. Optimal luminescence was achieved at a doping level of 2 wt% Dy3+, beyond which quenching effects reduced emission intensity. The critical quenching distance (R c) was estimated at 24.66 Å, indicating predominant non-radiative energy transfer. Moreover, thermal quenching was reduced, with the activation energy for thermal quenching determined to be 0.1975 eV, demonstrating that the material can maintain reasonable luminescence efficiency at elevated temperatures. Time-resolved photoluminescence spectroscopy revealed multi-exponential decay behavior, indicating the presence of multiple decay processes. The average luminescence lifetimes were calculated as 632 µs for the 2 wt% Dy3+ sample and 539 µs for the 3 wt% Dy3+ sample, with a clear concentration quenching effect observed at higher dopant levels. Colorimetric analysis in the CIE 1931 color space revealed a shift toward yellow with increasing Dy3+ concentration, achieving a correlated color temperature (CCT) of 6595 K at 2 wt% Dy3+. This shift supports the material's potential for photonic and lighting applications. These findings highlight a significant advancement in addressing the thermal stability issue in phosphor materials, making Dy3+-doped LMBO phosphors promising candidates for advanced photonic technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solution combustion method used to synthesize Ca 9 Gd(PO 4) 7 : Tb3+ nanophosphors. • Scherrer's and W-H method used for calculation of crystallite size. • PL quenching induced by quadrupole–quadrupole interaction was explained. • Schematic down-conversion mechanism explained. • Promising green emitting candidate for WLEDs. In present work, it is reported that Tb3+ doped Ca 9 Gd(PO 4) 7 phosphors synthesized via eco-friendly solution combustion method possess exceptional potential in lighting technology. Based on high-quality X-ray diffraction and advanced electron microscopy practices, structural and morphological properties of synthesized nanophosphors were investigated. The X-ray diffraction patterns recognized trigonal phase of R3c (161) space group with size in the range of 45–60 nm evaluated via Scherrer's and W-H method. Photoluminescent properties investigated via excitation under 379 nm radiance, suggest intense absorption in 400–600 nm (attributed to vivid green emission peaking at 547 nm). Quadrupole-quadrupole interactions results in cross relaxation among Tb3+ ions resulting in concentration quenching as explained via Dexter's and Van-Uitert's theoretical model. Auzel's method expressed value of radiative decay lifetime for the quantum mechanical state 5D 4. Optical band-gap of optimized nanophosphor is 4.05 eV, revealed by Tauc's hypothesis. Colorimetric investigations displayed excellent features which validated potential applications of Ca 9 Gd(PO 4) 7 : Tb3+ nanophosphors in optoelectronic technology. [ABSTRACT FROM AUTHOR]

In this study, we investigate the structural and photoluminescence (PL) properties of rare-earth-doped GdCa 4 O(BO 3) 3 (GdCOB) phosphors, specifically focusing on the spectral behaviour induced by doping with Eu³⁺ and Tb³⁺ ions. The powder X-ray diffraction (XRD) spectra confirm the formation of a monoclinic phase. The XRD data were also refined by a Rietveld refinement method. The existence of B, O, Ca, Gd, Tb, Eu and K elements was verified by EDS spectra. We introduce a detailed examination of the charge compensation process using Kröger-Vink notation to clarify the mechanisms essential for tailoring the optical properties of the phosphors. The PL excitation spectrum of GdCOB:Eu3+, monitored at 611 nm, reveals sharp excitation peaks at 319, 361, 380, and 392 nm, corresponding to 7F 0 →5H 3 , 7F 0 →5D 4 , 7F 0 →7F 0 , and 7F 0 →5L 6 transitions, respectively. The PL spectrum under excitation of 392 nm exhibits that phosphors doped with Eu3+ a significant red emission at 611 nm, which is attributed to the 5D₀→7F₂ transition. This emission intensity is particularly enhanced at non-centrosymmetric sites of the Eu³⁺ ions. Similarly, the PL excitation spectrum of GdCOB:Tb3+, monitored at 552 nm, displays distinct excitation peaks at 316, 341, 353, and 379 nm, which correspond to the transitions 7F₆→5D₀, 7 F₆→5L₇, 7F₆→5D₂, and 7F₆→5D₃, respectively. Tb³⁺-doped phosphors display a bright green emission, with a dominant peak at 552 nm, resulting from the 5D₄→7F₅ transition. Additionally, the introduction of K⁺ ions as co-dopants results in modifications to the local environments of Eu³⁺ and Tb³⁺ ions. These changes allow for fine-tuning of the emission peaks, significantly enhancing the luminescent output of the phosphors. Optimal doping concentrations of 5 mol% for Eu³⁺ and 1 mol% for Tb³⁺ enhance luminescent intensity and prevent concentration quenching. This phenomenon, often resulting in reduced PL intensity at higher dopant levels, is primarily due to dipole-dipole interactions, consistent with Dexter's theory of energy transfer. Strategic modulation of doping concentrations, coupled with a deep understanding of energy transfer mechanisms are critical for the development of advanced luminescent materials Our analysis of the Commission de l′Eclairage (CIE) chromaticity coordinates reveals enhanced energy transfer dynamics in rare-earth-doped borates, facilitating the tuning of luminescent properties. These results not only deepen our understanding of the fundamental physics governing such phosphors but also open pathways for the development of optoelectronic applications requiring consistent color output, such as LED technologies and solid-state lighting. [Display omitted] • Eu and Tb doped GdCa4O(BO3)3 phosphors synthesized via sol-gel microwave combustion. • K+ co-doping further enhances Eu and Tb-doped GdCa4O(BO3)3 luminescence. • Optimal Eu3+ and Tb3+ levels identified for peak emission. • Concentration quenching observed beyond optimal doping. • CIE analysis confirms consistent color output for tech applications. [ABSTRACT FROM AUTHOR]

This study explores the structural and luminescent properties of terbium (Tb³⁺)-doped lanthanum aluminium borate (LaAl₂B₄O₁₀, abbreviated as LAB) phosphors, a novel host lattice for Tb³⁺ doping. LAB:Tb³⁺ phosphors, with varying dopant concentrations, were synthesized using a microwave-assisted combustion synthesis approach and characterized using X-ray diffraction (XRD), Rietveld refinement, and photoluminescence spectroscopy at both room and low temperatures. The structural analysis confirmed the hexagonal crystal structure of LAB and revealed successful incorporation of Tb³⁺ ions without altering the fundamental lattice. Luminescence studies demonstrated that the LAB:Tb³⁺ phosphors show strong green emission primarily attributed to the 5D 4 →7F 5 transition of Tb³⁺. The optimal doping concentration was determined to be 5 wt% Tb³⁺, which provided maximum luminescence efficiency. This concentration also allowed for a critical study of energy transfer mechanisms within the phosphor, revealing dipole-dipole interactions with a critical distance of 9.80 Å between Tb³⁺ ions. Additionally, the CIE chromaticity coordinates of LAB:0.05 Tb³⁺ were precisely determined to be (0.289, 0.4460), indicating the potential for high-quality green emission suitable for solid-state lighting and display technologies. This work not only demonstrates the potential of LAB:Tb3+ as a highly efficient green luminescent material, but also sheds light on the mechanisms responsible for energy transfer and concentration quenching. • Tb³⁺-doped LaAl₂B₄O₁₀ phosphors synthesized for green luminescence. • Photoluminescence properties studied at room and low temperatures. • Concentration quenching analysed for Tb³⁺ in LAB phosphors. • Rietveld analysis confirms hexagonal structure of LAB. • CIE chromaticity shows color shift with Tb³⁺ concentration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dy3+ doped La 2 (WO 4) 3 were prepared by microwave assisted co-precipitation method. • Judd Ofelt intensity parameters were calculated and they follow the trend Ω 2 > Ω 6 > Ω 4. • Emission spectra contain peaks due to the transitions 4F 9/2 → 6H 15/2,13/2. • The optimum concentration of Dy3+ ions in La 2 (WO 4) 3 was found to be 10%. • CIE coordinates confirm the suitability of the phosphor for yellow emission. The synthesis and detailed luminescence studies of a series of La 2-x Dy x (WO 4) 3 (x = 0.02, 0.1, 0.2, 0.4, 0.6, 0.8) phosphors synthesized via microwave-assisted co-precipitation technique is reported in this paper. The XRD analysis confirmed that the phosphors were crystalized in a monoclinic structure with space group C 2/ c and FTIR analysis identified the characteristic vibrational modes. Morphological studies were conducted using FESEM analysis, and the EDS technique substantiated the effective incorporation of Dy3+ ions in La 2 (WO 4) 3. The photoluminescence excitation and emission spectra of varying concentrations of Dy3+ ions were recorded and an optimum concentration of 10% exhibited the highest intensity. The emission spectra of all phosphors were dominated by peaks at 484 nm and 574 nm. The radiative properties were evaluated using Judd-Ofelt analysis and the JO intensity parameters followed the trend Ω 2 > Ω 6 > Ω 4. The gradual decrease in the decay lifetime value of 4F 9/2 excited level with an increase in doping concentration elucidates concentration quenching phenomena due to dipole – quadrupole interaction. The emission data were also analyzed by calculating CIE coordinates and concluded that Dy3+ doped La 2 (WO 4) 3 phosphors have potential applications in yellow light generation. [ABSTRACT FROM AUTHOR]

KLaSiO4:Tb3+ phosphors were synthesized using the sol–gel method. The structure and luminescence properties of the materials were characterized using X‐ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry–differential thermal analysis, fluorescence spectra and calculated Commission Internationale de l'éclairage coordinates. The results showed that the material had a hexagonal structure, and that doping of Tb3+ did not change the crystal structure of KLaSiO4. FTIR spectroscopy confirmed the existence of stretching vibrations of Si–O, bending vibrations of Si–O–Si, and asymmetric tensile vibrations of Si–O in KLaSiO4. The excitation spectrum of the sample consisted of 4f7→5d1 broadband absorption and the characteristic excitation peak of Tb3+, the excitation peak at 232 nm belongs to the spin allowed 7FJ→7DJ transition of Tb3+, the excitation peak at 268 nm belongs to the spin forbidden 7FJ→9DJ transition of Tb3+, and the absorption band of 7FJ→7DJ transition is split. Under excitation at 232 nm, the emission peak of the sample was composed of the 5D4→7FJ (J = 6, 5, 4, 3) energy level transition of Tb3+. The highest emission peak is located at 543 nm, which belongs to the 5D4→7F5 transition and emits green light. Concentration quenching occurred when the Tb3+ doping concentration was greater than 1% mol, the quenching mechanism was an electric dipole–electric dipole action. When the ratio of citric acid to total metal ions was 1:1 and the annealing temperature was 800°C, the surface defects of the phosphors were greatly reduced, the quenching effect was reduced, and the luminous intensity reached the maximum. [ABSTRACT FROM AUTHOR]

An efficient, low-energy technique named solution-combustion synthesis was taken into use to generate a sequence of BaY(1−x)Zn3AlO7:xTb3+ (x = 0.01–0.10) nanophosphor. The powder X-ray diffraction patterns braced by Rietveld refinement established the sustenance of BaYZn3AlO7 lattice having hexagonal phase with space group P63mc (186). The most bulging peak in emanation spectra of the nanostructure at 543 nm was due to 5D0 → 7F2 electronic transition resulting in a green emission when excited by a near-UV light source (λmax = 278 nm). The quantum efficiency for the optimized sample was found out to be 78%. The synthesized nanophosphor with an optimum concentration of Tb3+, i.e., BaY0.95Tb0.05Zn3AlO7, and the standard host were characterized by DRS (diffuse reflectance spectroscopy), and bandgaps were evaluated which were found to be 4.63eV and 4.67eV respectively. The color coordinates also existed in the greenish section of the chromaticity diagram (x = 0.221 and y = 0.46). The CCT (correlated color temperature) was also evaluated for whole series of nanophosphors and found to be 1714 K for the optimized one that confirmed its applications in warm LED's fabrication. [ABSTRACT FROM AUTHOR]

The fluorescence coumarin derivatives were synthesised by an efficient one-pot, three-component reaction in 80–90% yields. The optical properties of these coumarin derivatives (4a-4d), such as the influence of different solvent to the fluorescence intensity and absorption intensity, and the influence of different substituent groups and the concentration of the solution are investigated. The results show that the fluorescence intensity of the compounds are the largest in the DMF（N,N-dimethyllformamide). Specifically speaking, the absorption spectrum is at approximately 308 nm, the fluorescence spectrum is at nearly 435 nm in the DMF, the Stocks shift approaches127 nm. In our case the fluorescence intensity decreases with the increase of the concentration of the solution, which is called concentration quenching. Additionally, the affection of solvent was also confirmed by TD-DFT (Time-dependent density functional theory)calculations.

Rare-earth element-free fluorescent materials are eco-friendlier than other traditional fluorescent precursors, such as quantum dots and phosphors. In this study, we explore a simple and facile solution-based technique to prepare fluorescent films, which are highly stable under ordinary room conditions and show hydrophobic behaviour. The proposed hybrid material was designed with hybrid composites that use polyvinyl butyral (PVB) as a host doped with organic dyes. The red and green fluorescent films exhibited quantum yields of 89% and 80%, respectively, and both are very uniform in thickness and water resistant. Additionally, PVB was further compared with another polymeric host, such as polyvinylpyrrolidone (PVP), to evaluate their binding ability and encapsulation behaviour. Next, the effect of PVB on the optical and chemical properties of the fluorescent materials was studied using UV spectroscopy and Fourier transform infrared spectroscopy. The analysis revealed that no new bond was formed between the host material and fluorescent precursor during the process, with intermolecular forces being present between different molecules. Moreover, the thickness of the fluorescent film and quantum yield relation were evaluated. Finally, the hydrophobic nature, strong binding ability, and optical enhancement by PVB provide a powerful tool for fabricating a highly efficient fluorescent film with enhanced stability in an external environment based on its promising encapsulation properties. These efficient fluorescent films have a bright potential in colour conversion for next-generation display applications.

GdVO4 : Eu3+ nanophosphors co‐doped with alkali metal ions (Li+, Na+, K+) of various concentrations were fabricated by an efficient hydrothermal method. The microstructure and luminescent emission properties were tested systematically. The results demonstrated that the co‐doping of M+ led to lattice distortion, which is closely related to dopants' ionic radii and concentrations. The lattice distortion further resulted in a fluctuation of luminescent brightness. The optimal luminescent properties of GdVO4 : Eu3+ co‐doped with Li+(10 atom‐% (at. %)), Na+(8 at. %), K+(6 at. %) were achieved respectively. Among them, the GdVO4 : Eu3+ co‐doped with Li+ of 10 at % possessed the highest emission intensity. Moreover, the alkali metal ions co‐doping also gave rise to the elevation of the concentration quenching threshold of Eu3+, which further enhanced the luminescent performance. [ABSTRACT FROM AUTHOR]

Doping sensitivity is a great obstacle in boosting thermally activated delayed fluorescence (TADF)‐based organic light‐emitting diodes into practical application. Herein, a "side by side" donor alignment strategy is proposed to achieve decent electroluminescence performance under high doping concentration by studying the structure–property relationship of two emitters D2T‐TRZ and D2Y‐TRZ. D2T‐TRZ containing parallel aligned donors shows high photoluminescent quantum yield (PLQY) and short delayed lifetime (τd) in both doped and neat films, which endow its excellent performances with maximum external quantum efficiencies (EQEmaxs) higher than 22% under wide doping range of 10–70 wt%. While, composed of antiparallel acridans, D2Y‐TRZ presents good PLQY and relatively long τd when diluted in host matrix, but undergoes severe quenching in neat films. Consequently, D2Y‐TRZ achieves lower EQEmaxs of 14.9–16.4% within narrow range of 10–40 wt%. This result reveals parallel aligned donors as a better choice to design TADF emitters inert to doping concentration. [ABSTRACT FROM AUTHOR]

Efficient orange-emitting SmxY1−xSr2SbO6 phosphors, which can be excited by the UV light at 405 nm and hence emit bright orange light, have been successfully prepared by the traditional high-temperature solid-state method. The phosphors were characterized by X-ray diffraction patterns, SEM, photoluminescence spectra, diffuse reflectance spectra, temperature-dependent luminescence spectra and decay properties in detail. The optimum doping concentration and critical energy transfer distance of SmxY1−xSr2SbO6 were determined from the photoluminescence spectra of as-prepared samples with different Sm3+ ions. The good thermal stability of SmxY1−xSr2SbO6 was also illustrated by temperature-dependent spectra of the SmxY1−xSr2SbO6 phosphors at temperature from 293 to 453 K. These merits demonstrated that SmxY1−xSr2SbO6 could be a potential candidate as an orange-emitting component applied in phosphor-converted warm WLED. [ABSTRACT FROM AUTHOR]

Upconversion materials capable of converting low-energy excitation photons into high-energy emission photons have attracted considerable interest in recent years. However, the low upconversion luminescence seriously hinders the application of upconversion phosphors. Heavy lanthanide doping without concentration quenching represents a direct and effective method to enhance the emission intensity. In this study, Er3+ heavy doped Gd2(MoO4)3 phosphor with a monoclinic phase was prepared by a sol–gel process. Under excitation at 976 nm, Gd2(MoO4)3:Er3+ phosphor emitted remarkably intense green emission, and Er3+ concentration up to 20 mol% did not cause concentration quenching. Here, we discuss the upconversion mechanism and concentration quenching. When the Er3+ concentration was in the range of 30–60 mol%, the concentration quenching was governed by the electric dipole–dipole interaction, and when the concentration was greater than 60 mol%, the concentration quenching was controlled by the exchange interactions. The result provides a schematic basis for identifying a phosphor host with heavy lanthanide doping.

The SrSi 2 O 2 N 2 :Eu2+ green-emitting phosphor, as a member of oxynitride phosphors, could greatly enhance the color quality of the white-light conversed by single yellow-emitting phosphor. However, SrSi 2 O 2 N 2 :Eu2+ phosphors prepared by traditional solid-state ways normally consist hard agglomerates with unevenly dispersed particles and therefore suppress the luminescence properties. This research proposes a heterogeneous precipitation protocol where precipitation process is introduced, in order to produce a precursor in the first phase. And in the second phase, a high-temperature solid-state process is adopted for obtaining the final product. The main results show that, for an optimized SrSi 2 O 2 N 2 :Eu2+ phosphor prepared using our protocol, (1) the SrSi 2 O 2 N 2 :Eu2+ particles are faceted and with smooth faces and (2) the phosphor photoluminescence, external quantum efficiency, stability against thermal exposure, and physical stability consistently outperform the current commercially used product. This research essentially provides an economic way for production of solid-state lighting with enhanced color quality. [ABSTRACT FROM AUTHOR]

(Y1–xPrx)2O2Se solid solutions with х = 0.004, 0.008, 0.010, 0.012, and 0.020 have been prepared from oxides by ampule synthesis. We have measured their excitation spectra at λem = 514 nm and their photoluminescence and quantum yield spectra at λex = 463 nm (T = 300 K). Comparing their emission intensities at wavelengths of 514 (3P0 → 3H4 transition) and 670 nm (3P0 → 3F2 transition), we have determined the optimal dopant concentration (x = 0.01), at which the quantum yield has a maximum, reaching 3%. [ABSTRACT FROM AUTHOR]

• Li 2 ZnTi 3 O 8 :Eu3+ phosphors were synthesized by solid state reaction method. • Intense red emission at 612 nm under 309 and 393 nm excitations. • The internal quantum efficiency was 48.91 %. • Possess excellent thermal stability, high color purity and warm CCT values. • Potential candidate to be used in pc-WLEDs under UV excitation. Embracing phosphor converted white light-emitting diodes (pc-WLEDs) represent a significant step towards efficient and sustainable energy sources, herein we report the synthesis, structural and optical properties of Eu3+ doped Li 2 ZnTi 3 O 8 phosphor for the first time. A series of Li 2(1- x) ZnTi 3 O 8 : x Eu3+ phosphors (x = 0, 0.02, 0.05, 0.08, 0.1 and 0.3 mol) were prepared by the high temperature solid state reaction method. The structural and morphological characterisation of prepared samples were done using X -ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FTIR) spectroscopy. The XRD analysis confirmed the cubic structure and purity of the samples with the incorporation of Eu3+ ions. The presence of functional groups was detected from FTIR and compositional elements from EDX. FESEM and TEM images revealed similar agglomerated block like structures. The optical properties were analysed using diffuse reflectance spectrum (DRS) and photoluminescence (PL) spectra. Under 309 and 393 nm excitation, characteristic emission peaks of Eu3+ ions corresponding to 5D 0 → 7F J (J = 0,1,2,3 and 4) transitions were observed in which the intense emission was recorded at 612 nm. Under both the excitations, the optimum concentration of prepared phosphor was 8 mol% (x = 0.08 mol) and the mechanism for concentration quenching was found to be dipole - dipole interaction. The decay lifetime of prepared phosphors was in the milliseconds range and the internal quantum efficiency was measured to be 48.91 %. Li 2(1- x) ZnTi 3 O 8 : 0.08Eu3+ phosphor has an activation energy of 0.163 eV and holds good thermal stability. Also, for the optimum sample, the Commission International de I'Eclairage (CIE) coordinates were detected at (0.6333, 0.3663) and (0.6344, 0.3651) for 309 and 393 nm excitation respectively, which lies in the orange - red region with super color purity and warm correlated color temperature (CCT) values. Therefore, obtained results suggest that the prepared Li 2(1- x) ZnTi 3 O 8 : x Eu3+ phosphors are suitable candidates for its use in pc-WLEDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ce3+ and Tb3+ doped NaBaBO 3 were synthesized by combustion method. • Temperature-dependent behavior of Ce3+ and Tb3+ doped NaBaBO 3. • Identified optimal Ce3+, Tb3+ doping levels. • New insights into cross-relaxation mechanisms presented. • Dipole interactions key to emission intensity. This study explores the structural and temperature-dependent photoluminescence of Ce3+ and Tb3+ doped NaBaBO 3 phosphors, synthesized via combustion. Analysis of their crystal structures confirmed excellent alignment with the standard PDF#98–008-0110. Investigation into both room and low-temperature photoluminescence revealed that the dopants have a significant effect on emission spectra. Ce3+-doped samples exhibited excitation peaks at 275 nm and 358 nm, leading to a primary emission at 419 nm, with enhanced low-temperature emission suggesting reduced non-radiative processes. Tb3+-doped phosphors showed excitation from 250 to 377 nm and emissions from blue to deep red, including strong green emission at 550 nm due to 5D 4 →7F 5 transitions. Optimal doping was found at 1 mol% for Ce3+, while Tb3+ showed increased luminescence up to 3 mol%, with concentration quenching observed beyond these points. The study indicates dipole–dipole interactions dominate Ce3+ concentration quenching, whereas Tb3+ involves both electric dipole and quadrupole interactions. This analysis provides insights into enhancing luminescent efficiency and suggests NaBaBO 3 : x Ce3+,Tb3+ phosphors' potential in advancing white LED technology, highlighting their stable luminescent properties at low temperatures. [ABSTRACT FROM AUTHOR]

This study explores the structural and optical qualities of LaCa 4 O(BO 3) 3 (LACOB) phosphors doped with Eu3+, Dy3+, and Tb3+ using a microwave-assisted sol-gel technique. It uncovers oxygen-related luminescence defects in LACOB, highlighting emission peaks at 489 and 585 nm for Dy3+, a distinct sharp peak at 611 nm for Eu3+ in the red spectrum, and a notable green emission for Tb3+ due to specific transitions. The photoluminescence (PL) analysis indicates that luminescence is optimized through precise doping, leveraging dipole interactions, and localized resonant energy transfer, which are influenced by dopant concentration and spatial configuration. Temperature studies show emission intensity variations, particularly noticeable below 100 K for Tb3+ doped samples, demonstrating the nuanced balance between thermal quenching and luminescence efficiency. This temperature dependency, alongside the identified optimal doping conditions, underscores the potential of these materials for advanced photonic applications, offering insights into their thermal behavior and emission mechanisms under different conditions. [Display omitted] • Novel Eu3+, Tb3+, and Dy3+ Doped LaCa 4 O(BO 3) synthesized phosphors by microwave-assisted sol-gel technique. • Optimal Eu3+, Dy3+ and Tb3+ levels identified for peak emission. • Concentration quenching observed beyond optimal doping. • CIE analysis confirms consistent color output for tech applications. [ABSTRACT FROM AUTHOR]

Gadolinium oxide nanostructures have been actively studied as multimodal materials for both technical applications and biomedical research. Doping of this oxide structure with a given concentration of chosen rare earth ions allows one to obtain predefined optical properties. Weakly agglomerated nanoscale and submicron Gd 2 O 3 :Tb3+ particles were synthesized by a modified Pechini method in a single chemical process. The nanoscale fraction was transferred into aqueous solution without the addition of surfactant. Zeta potential of this solution was found to be about −17 (±1) mV. The crystal structure of cubic gadolinium oxide is confirmed for the large and small size fraction. The optimal concentration of terbium ions, at which the highest luminescence is observed, was 1.2 at.%. The concentration quenching mechanism for Tb3+-doped Gd 2 O 3 samples was determined as a dipole–quadrupole energy migration with subsequent quenching on impurities. The luminescence properties of sub-micron and nanoparticles, including lifetimes, were found to be almost identical. The effect of temperature on both steady-state and kinetic luminescent properties was studied. Gd 2 O 3 :Tb3+ phosphors were found to be promising as lifetime-based luminescent thermometers. [Display omitted] • Gd 2 O 3 :Tb3+ concentration series was prepared with a modified Pechini method. • Gd 2 O 3 :Tb3+ powders contain submicron and nanoscale (<150 nm) fractions. • The highest luminescence intensity is observed for 1.2 at.% of Tb3+. • Luminescence kinetics is characterized by two lifetimes for both fractions. • Gd 2 O 3 :Tb3+ samples can be used as lifetime-based luminescent thermometers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bright red-emitting Ca 2 LuZr 2 Al 3 O 12 :Eu3+ phosphors are prepared. • They exhibit intense red emissions around 618 nm. • Color purity reaches 91.1%. • Thermal stability is excellent. In this work, a group of red-emitting Ca 2 LuZr 2 Al 3 O 12 : x Eu3+ (x = 20%, 30%, 40%, 50%, 60%, 70% and 80%) phosphors have been prepared and their luminescence properties are studied. X-ray diffraction, excitation and emission spectra, fluorescence decay curves, CIE color coordinates, and temperature-dependent photoluminescence spectra are used to characterize these samples. All these Ca 2 LuZr 2 Al 3 O 12 :Eu3+ compounds exhibit intense red luminescence peaking at around 618 nm under 394 nm excitation. The critical concentration of Eu3+ ion is 50 mol%, and the concentration quenching mechanism has been discussed and analyzed. The CIE color coordinates of the optimal Ca 2 LuZr 2 Al 3 O 12 :50%Eu3+ sample are (0.6506, 0.3487), and it has a high color purity of 90.7%. Importantly, the emission intensity of Ca 2 LuZr 2 Al 3 O 12 :50%Eu3+ is about 1.67 times higher compared to the commercial Y 2 O 3 :Eu3+ red phosphor. What's more, Ca 2 LuZr 2 Al 3 O 12 :50%Eu3+ phosphor also displays excellent resistance to thermal quenching at elevated temperature; only 14% emission intensity is lost at 150 °C. [ABSTRACT FROM AUTHOR]

An investigation into the luminescent behavior of YCOB (Yttrium Calcium Oxyborate) doped with Eu3+ and Dy3+ ions, synthesized via the combustion method, is presented. The study, employing X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Energy-Dispersive X-ray Spectroscopy (EDS) analyses, confirms the structural integrity and purity of the synthesized nanophosphors. An XRD pattern exhibiting distinct crystalline peaks indicates that the dopant ions were successfully integrated into the YCOB lattice. The photoluminescence (PL) response of YCOB with Eu3+ and Dy3+ ions is thoroughly examined, uncovering distinct excitation and emission spectra. In the case of Eu3+ doping, excitation spectra reveal a significant charge transfer (CT) band at 254 nm, indicative of electron transfer between oxygen and europium ions. This CT transition enhances our understanding of the excitation behavior, with the dominant and Laporte-forbidden 5D 0 → 7F 2 transition. Characteristic peaks at 345 nm in the excitation spectra efficiently stimulate YCOB:Dy3+ when Dy3+ is used as a dopant. The primary emission peak at 585 nm corresponds to the hypersensitive electric dipole transition 4F 9/2 –6H 13/2. Concentration quenching phenomena are observed, with a maximum Eu3+ concentration of 7 wt % attributed to the dipole-quadrupole interaction. Dy3+ doping, with a maximum concentration of 2 wt % primarily shows multipolar interactions, especially dipole-dipole interactions. The study extends to CIE chromaticity analysis, emphasizing Eu3+ doping's suitability for white light-emitting diode (WLED) applications and ensuring color stability. Conversely, varying Dy3+ concentrations do not yield consistent chromaticity coordinates. These findings have significant implications for the development of advanced phosphor materials across diverse applications, offering a roadmap for optimizing their optical performance. • Synthesized YCOB nanophosphors via combustion doping with Eu3+ and Dy3+. • Validated structural purity through XRD analysis of nanophosphors. • Identified optimal doping concentrations: 7 % for Eu3+ and 2 % for Dy3+. • Emphasized the suitability of Eu3+ doping for WLED applications, ensuring color stability. [ABSTRACT FROM AUTHOR]

Thermoluminescence (TL) analysis of gamma-irradiated SrZnO2:Dy nanophosphors elucidates the presence of various trapping centers in forbidden band. Raman and Fourier-transformed infrared spectra indicate effect on vibrational structure upon doping. Complex glow curves are obtained at varying gamma radiation doses, exhibiting glow features in low (50-180 °C) and high (220-400 °C) temperature regions. The deconvolution of glow curves indicates the presence of TL peaks at =100, 143, 202, 269, and 337 =C. The effect of Dy doping is observed as emergence of new glow feature at =143 °C. The substitution of trivalent Dy into SrZnO2 host having divalent cations is proposed to be creating Dy1þ X (X = Sr, Zn) electron traps and V²X- hole traps, along with hitherto existing intrinsic defects. The concentration quenching of TL signal is perceived at 3 mol% Dy doping, whereas comparing glow curves for all samples at saturation dose indicate quenching of low- and high-temperature glow features at different doping concentrations. The theoretical track interaction model and empirical three trap one recombination center (3T1R) model is used to explain former and latter effects, respectively. A schematic band model is proposed to predict the trap distribution upon Dy inclusion, responsible for observed TL in SrZnO2:Dy nanophosphors. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) luminescent materials have unparalleled advantages in certain fields, such as anti-counterfeiting. Nd3+ ion doped Gd 2 O 3 near-infrared phosphor was successfully prepared by co-precipitation method and high-temperature solid-phase reaction. The structure and morphology of Gd 2 O 3 :Nd3+ cubic phase phosphors were studied in detail. The prepared phosphor was optically analyzed by fluorescence spectrometer. The research results show that with the increase of the Nd3+ doping concentration, the luminous intensity of the near-infrared phosphor in the near-infrared region shows a trend of first increasing and then decreasing. When the Nd3+ ion doping concentration is 1.0 mol%, the obtained phosphors have the best luminous intensity in the near-infrared region under the excitation of 808 nm laser. Gd 2 O 3 :Nd3+ phosphor emits near-infrared light due to the intra-4 f transitions of Nd3+ ions. The concentration quenching theory is used to prove that the concentration quenching of Gd 2 O 3 :Nd3+ belongs to the cross relaxation caused by electric multipole. Due to the unique optical properties of this near-infrared phosphor, it is expected to be further developed in the field of fluorescent materials. [ABSTRACT FROM AUTHOR]

Novel reddish-orange-emitting Ca 2 GdNbO 6 :Sm3+ phosphors based on the emission of 4G 5/2 → 6H 9/2 transition at 651 nm with the chromatic coordinate of (0.633, 0.366) were synthesized. The crystal structure and chemical purity were identified in detail. Under the 407 nm excitation, the optimum concentration of Sm3+ ion was found to be 5 mol% dominated by the dipole-dipole interaction in the Ca 2 GdNbO 6 host material. The color purity of the sample with optimum doping was estimated to be about 78.38%. Besides, the thermal stability was also studied, and it was further found that the emission intensity remained 65.32% at 423 K. The packaged white LED device exhibited excellent CRI and CCT values of 92.43 and 4896 K. Finally, the polydimethylsiloxane film with a stable structure and flexible property was prepared. These above results reveal that novel reddish-orange-emitting Ca 2 GdNbO 6 :Sm3+ phosphors can be applied in high CRI white communication and flexible display applications. [ABSTRACT FROM AUTHOR]

Calcium borophosphate (CBP) phosphors doped with Dy3+ were synthesized by solid-state reaction method. These phosphors were characterized by photoluminescence spectra and decay curves in the visible region. These phosphors were excited at 350 nm, and emission spectra were studied. Decay curves were obtained for the transition, 4F9/2 → 6H13/2 of Dy3+, and lifetimes were measured for different concentrations of Dy3+ ions. CIE chromaticity coordinates were obtained for these Dy3+-doped CBP phosphors. Correlated color temperature was also calculated using the standard formula. [ABSTRACT FROM AUTHOR]

Simultaneously achieving a high photoluminescence quantum yield (PLQY), ultrashort exciton lifetime, and suppressed concentration quenching in thermally activated delayed fluorescence (TADF) materials is desirable yet challenging. Here, a novel acceptor-donor-acceptor type TADF emitter, namely, 2BO-sQA, wherein two oxygen-bridged triarylboron (BO) acceptors are arranged with cofacial alignment and positioned nearly orthogonal to the rigid dispirofluorene-quinolinoacridine (sQA) donor is reported. This molecular design enables the compound to achieve highly efficient (PLQYs up to 99%) and short-lived (nanosecond-scale) blue TADF with effectively suppressed concentration quenching in films. Consequently, the doped organic light-emitting diodes (OLEDs) base on 2BO-sQA achieve exceptional electroluminescence performance across a broad range of doping concentrations, maintaining maximum external quantum efficiencies (EQEs) at over 30% for doping concentrations ranging from 10 to 70 wt%. Remarkably, the nondoped blue OLED achieves a record-high maximum EQE of 26.6% with a small efficiency roll-off of 14.0% at 1000 candelas per square meter. By using 2BO-sQA as the sensitizer for the multiresonance TADF emitter ν-DABNA, TADF-sensitized fluorescence OLEDs achieve high-efficiency deep-blue emission. These results demonstrate the feasibility of this molecular design in developing TADF emitters with high efficiency, ultrashort exciton lifetime, and minimal concentration quenching., (© 2024 Wiley‐VCH GmbH.)

Microspheres composed of Y-containing materials are effective agents for cancer radioembolization therapy using β-rays. The distribution and dynamics of these microspheres in tissues can be easily determined by providing the microspheres with an imaging function. In addition, the use of quantum dots will enable the detection of microspheres at the individual particle level with high sensitivity. In this study, core - shell quantum dots were bound to chemically modified yttria microspheres under various conditions, and the effect of reaction conditions on the photoluminescence properties of the microspheres was investigated. The quantum dots were immobilized on the surfaces of the microspheres through dehydration - condensation reactions between the carboxy groups of quantum dots and the amino groups of silane-treated microspheres. As the reaction time increased, the photoluminescence peak blue shifted, and the photoluminescence intensity and lifetime decreased. Therefore, a moderate period of the immobilization process was optimal for imparting effective photoluminescence properties. This study is expected to facilitate particle-level tracking of microsphere dynamics in biological tissues for the development of minimally invasive cancer radiotherapy of deep-seated tumors., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2024 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis Group.)

Nanoparticles of xRe 2 O 3 – (100-x)CaWO 4 (Re = Eu, Dy, Sm; x = 0, 1, 3, 5, 7 and 10 mol%) were synthesized by solid-state sintering at two annealing temperatures of 800 °C and 1150 °C and characterized by neutron diffraction, Raman and photoluminescence (PL) spectroscopy. The samples are composite materials and contain tetragonal CaWO 4 and cubic Re 2 O 3 phases. The unit cell parameters, atomic position co-ordinates, crystallite size, mole-fraction of phases, bond-lengths, bond-angles and cation-oxygen co-ordination numbers were determined by Rietveld analysis of the neutron diffraction data. The short-range structure of CaWO 4 consists of snub disphenoid deltahedral CaO 8 and tetrahedral WO 4 units and the structure of cubic Re 2 O 3 consists of two types of ReO 6 units. All the W–O bonds in WO 4 units are of equal lengths (1.77–1.79 Å) whereas two kinds of slightly different Ca–O bond-lengths (2.41–2.45 Å and 2.45–2.47 Å) exist in CaO 8 units. The neutron pair distribution function of the undoped CaWO 4 samples shows the first peak in the range of 1.71–1.74 Å due to W–O bonds and the second peak at 2.84 Å due to O–O and Ca–O pair correlations. Raman studies of Eu-doped samples show only W–O vibration modes, however, Sm and Dy-doped CaWO 4 show weak Raman peaks of Sm 2 O 3 and Dy 2 O 3 , along with W–O bond vibrations. PL studies show highest orange-red emission at 1 mol% Sm 2 O 3 , green emission at 1 mol% Dy 2 O 3 and red emission at 3 mol% Eu 2 O 3. The light emission intensity in all the samples increases with the increase in annealing temperature from 800 °C to 1150 °C. [ABSTRACT FROM AUTHOR]

A series of Ba2YAlO5; 0.2Eu3+, xNa+(x =0. 01, 0. 03, 0. 05, 0. 10, 0. 20, 0. 30) phosphors were synthesized successfully by high temperature solid phase method. The effect of Eu3+, Na+ doping on the crystal structure was studied. Observe the morphology of fluorescent materials with scanning electron microscope. The excitation and emission optical properties of phosphors were observed and analyzed by fluorescence spectrometer. Conducted theoretical research on concentration quenching and energy transfer. Under 613 nm emission, O2 - →Eu3+ charge transfer band appears at 270 nm to 290 nm, peaks appear at 395 nm and 465 nm, the peak at 465 nm is the highest, corresponding to the 7F0 →5D2 transition. Under 465 nm excitation, it is observed that emission peak is the strongest at 613 nm, corresponding to the 5D0 →7F2 transition, and the optimal doping concentration of sodium ion is x = 0. 03. Theoretical calculation verified that the energy transfer in the host material is between the nearest neighbor ions. Thermal stability test analysis of the luminescent material show that activation energy of thermal quenching is 0. 058 eV, and color coordinates of Ba2YAlO5; 0.2Eu3+, 0.03 Na+ phosphors are calculated locate in (0. 61, 0. 39), which is very close to the standard chromaticity coordinates (0. 67, 0. 33) stipulated by the International Commission on Lighting. [ABSTRACT FROM AUTHOR]

Sm3+-doped LnNbO4 (Ln=La, Y) phosphors were obtained by high-temperature solid-state reaction. The crystal structure of LnNbO4:Sm3+ (Ln=La, Y) was characterized by X-ray diffraction. Luminescent properties of those phosphors were investigated by diffuse reflection spectra, excitation spectra, as well as emission spectra. The emission spectra of those phosphors consisted of several orangish-red emission bands around 550–670 nm upon the excitation at 405 nm, and the luminescent emission intensity of LaNbO4: Sm3+ was much stronger than that of YNbO4: Sm3+. The 87.0% energy transfer efficiency from the host to Sm3+ ions was observed in LaNbO4: Sm3+ phosphor. Furthermore, the critical transfer distance was calculated and the CIE chromaticity coordinates of LaNbO4: Sm3+ samples were in the range of orangish-red. The fluorescence lifetimes of as-prepared LaNbO4: Sm3+ samples were within the millisecond range and the temperature-dependent luminescence indicated LaNbO4: Sm3+ was highly thermal-stable. Our results indicated that novel orangish-red-emitting LnNbO4: Sm3+ (Ln=La, Y) phosphors were expected to have great potential in white LEDs. [ABSTRACT FROM AUTHOR]

Ordered SiO2:Er3+ inverse opal films are fabricated by sol–gel technique in combination with a self‐assembly method to examine their potential as a suitable platform to tailor the spontaneous emission lifetime of Er3+ ions and its concentration quenching (CQ). Good ordering on long‐range scale is evidenced by means of scanning electron microscopy, whereas reflectance measurements display a green bright color, as it results from optical Bragg diffraction from the (111) crystal planes. Moreover, it is observed that the spontaneous decay rates (SDRs) of the inverse opals are suppressed, in contrast to the corresponding reference samples, due to the modulation of the effective refractive index (neff), in agreement with the virtual cavity model. At the same time, the reduced CQ of Er3+ is attributed to the periodic empty cavity of the inverse opals. These results demonstrate that inverse opals can provide a tool for the enhancement of near‐infrared (NIR) luminescence. [ABSTRACT FROM AUTHOR]

Ca2Al2SiO7:x.Sm3+ (x = 0.5, 1.0, 1.5, 2.0, 2.5, and 3.5 mol.%) (CAS:x.Sm3+) phosphors were synthesized by a solid-state reaction technique. The structure, photoluminescence properties and thermal stability of phosphors were investigated in detail. Results of X-ray diffraction show that CAS:x.Sm3+ materials have a single-phased tetragonal structure, and an expansion of the unit cell relates to the increasing of Sm3+ concentration. Photoluminescence study displayed that the CAS:x.Sm3+ phosphors reach the highest emission intensity at 1.5 mol.% Sm3+ and achieved the luminescence quenching phenomenon a higher concentration. The dominant interaction mechanism of the concentration quenching process is determined due to the dipole–dipole interaction, and the critical transfer distance (Rc) is 26.7 Å. The temperature dependence of photoluminescence spectra indicates that the Ca2Al2SiO7:Sm3+ (1.5 mol.%) phosphor possess good thermal stability, and that the activation energy is around 0.12 eV (968 cm−1). Several characteristic vibrations in the 200–1000-cm−1 region were observed by Raman spectra, and the color chromaticity coordinates of the samples were also calculated and discussed. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) emitters are typically embedded at low concentrations in a host matrix to suppress emission quenching. However, recent studies indicate that TADF compounds such as the oBFCzTrz emitter (5‐(2‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐5H‐benzofuro[3,2‐c]carbazole) display insignificant concentration quenching dependence. To understand the origin of this beneficial behavior, the morphology, dynamics, electronic properties, and charge transport and energy transfer in a neat film of the oBFCzTrz emitter are characterized via molecular dynamic simulations combined with density functional theory calculations. The emissive layer shows glassy behavior at room temperature with the twisted configurations of the emitter molecules allowing for intramolecular donor–acceptor interactions, but disfavoring intermolecular π–π stacking, which suppresses the formation of intermolecular aggregate states. As a result, the electronic structure and luminescence of oBFCzTrz are not significantly altered by intermolecular interactions. The calculated diffusion lengths of the singlet and triplet excitons are small enough that there occurs no substantial concentration quenching effect. Overall, the design of new TADF emitters with structural motifs similar to those of oBFCzTrz offers potential to develop efficient organic light‐emitting diode devices in which the emissive layers are entirely composed of TADF molecules without the need for a host component. [ABSTRACT FROM AUTHOR]

The ternary mixed metal oxides with high specific surface area are industrially important for sensors, catalysis, energy storage, and optoelectronics. However, synthesis of such metal oxides is always challenging, especially when multicomponent mixtures occur due to very narrow formation temperature windows. Flame spray pyrolysis is one of the best known techniques which enable formation of pure phases optimizing the temperature profile via control over the fuel/oxidizer ratio. Here, Y4Al2O9 (monoclinic phase of yttrium aluminum oxide, also known as YAM) and Y4–xEuxAl2O9 (x = 0.05–1.0) were strategically synthesized with specific precursor–solvent chemistry. While the hydrated yttrium nitrate with 28.2% water was unsuitable for the formation of crystalline Y4Al2O9 particles, the use of organic precursor–solvent combinations (Y/Al 2:1) resulted in 16 nm phase pure, highly crystalline Y4Al2O9 particles. All the materials were characterized by using X-ray diffraction with Rietveld refinement, Raman spectroscopy, and transmission electron microscopy. To develop a stable light-converting phosphor, the Y4Al2O9 host was doped with Eu to investigate the photoluminescence properties of Y4–xEuxAl2O9 (x = 0.05–1.0). The results indicated increased photoluminescence intensity with increasing Eu3+ concentration up to x = 0.5, i.e., Y3.5Eu0.5Al2O9, and a subsequent drop or decrease in intensity for x ≥ 0.7. Hence, Y3.5Eu0.5Al2O9 is proposed for a potential light-converting phosphor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Extensive investigations were conducted on the structural and photoluminescence characteristics of the present nanosamples, encompassing PL, TEM, PXRD, EDAX, CCT, and CIE research. PXRD studies established a single phase, and TEM instruments were used to examine the dimensions and topographical behavior. The EDAX analysis examined the magnitude of the different components that were present. Decay lifetimes, radiative and non-radiative energy transfer rates, and a number of intensity limitations have all been found using PL spectra. Two significant peaks were visible in the blue (B) and yellow (Y) regions of the photoluminescence (PL) spectra upon NUV excitation, at 486 nm and 577 nm. At 7 mol% Dy3+ ions, the PL intensity peaked. After that, it began to decline as a result of the concentration quenching process brought on by multipolar exchanges (s = 4.1445). The values of 0.86423 ms, 81%, and 226 s−1 were discovered to be the decay life time, non radiative rates, and quantum efficiency of the ideal powder, respectively. Further analysis of Sr3Y0.93Dy0.07(PO4)3 nanocrystals revealed that their chromaticity coordinates (0.305, 0.321), and CCT value (6902 K) matched those of NTSE and commercial LEDs, certifying their use in innovative optoelectronic appliances, particularly single phased WLEDs. [ABSTRACT FROM AUTHOR]