Eu2+‐Doped Yellow‐Emitting CsBaB3O6 Glass‐Ceramic Prepared by Melt Quenching and Re‐Crystallization Method

Eu³⁺‐doped cesium barium borate glass with the composition of Cs₂O·2BaO·3B₂O₃ was prepared by the conventional melt quenching method. The glass‐ceramic sample was obtained from the re‐crystallization of the as‐made glass to change the amorphous glass into a crystalline host. This reduces the Eu³⁺ in glass to Eu²⁺ ions resulting in a yellow‐emitting phosphor of Eu²⁺‐activated CsBaB₃O₆. The samples were investigated by the XRD patterns and SEM micrograph, the optical absorption, the photoluminescence spectra, and decay curves. The as‐made glass has only Eu³⁺ centers. Under the excitation of blue or near‐UV light, Eu²⁺‐doped CsBaB₃O₆ presents yellow‐emitting color from the allowed inter‐configurational 4f–5d transition in the Eu²⁺ ions. The maximum absolute luminescence quantum efficiencies of Eu²⁺‐doped CsBaB₃O₆ phosphor was measured to be 47% excited at 430 nm light at 300 K. By taking into account the efficient excitation in blue wavelength region, this new phosphor could be a potential yellow‐emitting phosphor for an application in white light‐emitting diodes fabricated with blue chips.     

Color-tunable and white emission of Tm3+ doped transparent zinc silicate glass-ceramics embedding ZnO nanocrystals

Tm³⁺ doped zinc silicate glass-ceramics composed of SiO₂-Al₂O₃-ZnO-K₂O-Tm₂O₃ embedded with ZnO nanocrystals were successfully fabricated by melt-quenching method with subsequent heat treatment. Tm³⁺ ions and ZnO nanocrystals were introduced as blue and yellow luminescence centers, respectively. The effects of heat treatment, excitation wavelength and Tm³⁺ doping concentration on the photoluminescence behaviors of these glass-ceramics were studied. Short-time (5 minutes) heat treatment was considered as the optimal heat treatment time, which facilitates simultaneously emitting narrow blue peak located at 453 nm and a broad yellow band centered at 580 nm. Blue and yellow emissions could be attributed to the ¹D₂ → ³F₄ transition of Tm³⁺ and Zn_i/O_i-related defect emission of ZnO nanocrystals, respectively. The combination of these two emissions allows the realization of white light emitting in the glass-ceramic samples. Furthermore, tunable luminescent color and chromaticity coordinates, including yellow, white and blue, can be realized by varying the pumping wavelengths as well as the content of Tm³⁺ dopant in the glass matrix. Nearly perfect white light emission with Commission Internationale de l'Eclairage coordinate (x = 0.33, y = 0.32) was achieved for the 0.05 mol% Tm³⁺ doped glass-ceramic embedding ZnO nanocrystals by heat treatment at 750°C for 5 minutes under the excitation of 360 nm. These luminescent glass-ceramics doped with Tm³⁺ ion and ZnO nanocrystals could be a promising candidate for white light emitting devices under near-ultraviolet excitation.     

Improving white light emission and quantum yield of Ce@Eu co-doped silicate glass by reducing Eu3+ to Eu2+ with Si3N4

Rare-earth-doped transparent glass shows great potential in white light-emitting diodes (wLEDs) application due to its excellent optical and luminous properties. Currently reported commercial wLEDs have a drawback in red emission missing, which leads to a relatively low color rendering index (CRI) and a relatively high correlated color temperature (CCT). In this work, Ce@Eu Sr–Si–O glass is fabricated using a high-temperature quenching method. The white light is available when the ratio of Ce³⁺/Eu³⁺ equals 1, and the emitting color can be adjusted from blue to red by controlling the ratio of Ce³⁺/Eu³⁺. To further optimize the white light, Eu³⁺ ions can be reduced to Eu²⁺ according to the reaction of 6Eu³⁺ + 2N³⁻ → 6Eu²⁺ + N₂↑ by introducing Si₃N₄. As a result, the standard white light emission can be achieved in the Ce@Eu silicate glass contributed by the blue light from Ce³⁺, red light from Eu³⁺, and yellow–green light from Eu²⁺ (two elements, three emission). This glass shows excellent luminous properties, such as a color coordinate is (0.3651, 0.3269) in CIE 1931 color coordinate diagram, a CRI is over 70, a high quantum yield of 36.02%, and a CCT of 4117 K.     

Thermal,Structural, and Enhanced Photoluminescence Properties of Eu3+‐doped Transparent Willemite Glass–Ceramic Nanocomposites

The precursor glass in the ZnO–Al₂O₃–B₂O₃–SiO₂ (ZABS) system doped with Eu₂O₃ was prepared by the melt‐quench technique. The transparent willemite, Zn₂SiO₄ (ZS) glass–ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat‐treatment time was examined by X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18–70 nm whereas the grain size observed in FESEM is 50–250 nm. The refractive index value is decreased with increase in heat‐treatment time which is caused by the partial replacement of ZnO₄ units of ZS nanocrystals by AlO₄ units due to generation of vacancies. Fourier transform infrared (FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass‐ceramics compared with its precursor glass. The photoluminescence spectra of Eu³⁺ ions exhibit emission transitions of ⁵D₀→⁷F_j (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 17‐fold with the process of heat treatment. This enhancement is caused by partitioning of Eu³⁺ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass–ceramic nanocomposites are expected to find potential applications in solid‐state red lasers, phosphors, and optical display systems.     

Luminescence properties of Eu2+ and Mn2+ doped Sr1.7Mg0.3SiO4 phosphors

Eu²⁺, Mn²⁺ doped Sr_1.7Mg_0.3SiO₄ phosphors were prepared by high temperature solid-state reaction method. Their luminescence properties were studied. The emission spectra of Eu²⁺ singly doped Sr_1.7Mg_0.3SiO₄ consist of a blue band (455 nm) and a green band (550 nm). The relative intensities of two emissions varied with Eu²⁺ concentration. Eu²⁺ and Mn²⁺ co-doped Sr_1.7Mg_0.3SiO₄ phosphors emit three color lights and present whitish color. The blue (455 nm) and green (550 nm) emissions are attributed to the transitions of Eu²⁺, while the red (670 nm) emission is originated from the transition of Mn²⁺ ion. The results indicate the energy transfer from Eu²⁺ to Mn²⁺. The mechanism of the energy transfer is resonance-type energy transfer due to the spectral overlap between the emission of Eu²⁺and the absorption of Mn²⁺.     

Impact of Eu3+ Dopants on Optical Spectroscopy of Ce3+: Y3Al5O12‐Embedded Transparent Glass‐Ceramics

Transparent glass‐ceramics containing Ce³⁺: Y₃Al₅O₁₂ phosphors and Eu³⁺ ions were successfully fabricated by a low‐temperature co‐sintering technique to explore their potential application in white light‐emitting diodes (WLEDs). Microstructure of the sample was studied using a scanning electron microscope equipped with an energy dispersive X‐ray spectroscopy. The impact of co‐sintering temperature, Ce³⁺: Y₃Al₅O₁₂ crystal content and Eu³⁺ doping content on optical properties of glass‐ceramics were systematically studied by emission, excitation spectra, and decay curves. Notably, the spatial separation of these two different activators in the present glass‐ceramics, where Ce³⁺ ions located in YAG crystalline phase while the Eu³⁺ ones stayed in glass matrix, is advantageous to the realization of both intense yellow emission assigned to Ce³⁺: 5d→4f transition and red luminescence originating from Eu³⁺: 4f→4f transitions. As a result, the quantum yield of the glass‐ceramic reached as high as 93%, and the constructed WLEDs exhibited an optimal luminous efficacy of 122 lm/W, correlated color temperature of 6532 K and color rendering index of 75.     

Eu3+-doped transparent potassium lanthanum silicate (KLaSiO4) glass-ceramic nanocomposites: Synthesis,properties and application

The preparation of Eu³⁺-doped novel K₂O-La₂O₃-Al₂O₃-SiO₂ (KLAS)-based glass and transparent KLS (KLaSiO₄) glass–ceramic (GC) nanocomposites is reported. Nanostructures of the transparent GCs were analyzed by FE-SEM, H(R)-TEM and SAED techniques. The average size of the crystallites is calculated using XRD data and found to be in the range 13–19?nm which is matched well with the average particle size observed from TEM images in the range 5–18?nm. Photoluminescence spectra of Eu³⁺ ions exhibit emission transitions of ⁵D₀?→?⁷F_j (j?=?0 and 1–4) under the excitation at 394?nm. The emission spectra reveals up to 3-fold enhancement of luminescence performance of the KLS GC nanocomposites compared to as-prepared glass. This enhancement is caused due to entering of Eu³⁺ ions into the KLS crystal sites by replacing the La³⁺ ions. Such luminescence properties of KLS glass-ceramic nanocomposites could be a promising candidate as laser host for many laser devices.     

Ion-exchanged LTA zeolite derived nepheline phase NaAlSiO4:Eu2+ ceramic phosphor for laser illumination

A reliable yellow phosphor converter that can be efficiently excited by a 405 nm bluish violet laser is in high demand for laser illumination applications. A NaAlSiO₄:Eu²⁺ phosphor with a quantum efficiency reaching 92% was obtained using LTA zeolite as the raw material. NaAlSiO₄:Eu²⁺ ceramics with suitable porosities for laser illumination were prepared from the phosphor powders via spark plasma sintering. The ceramics lost only 2% of the quantum efficiency compared to the powders, maintained good thermal quenching properties (30% drop at 150 °C), and showed good thermal conductivity (2.02 W‧m⁻¹‧K⁻¹). The NaAlSiO₄:Eu²⁺ ceramic with 405 nm bluish violet lasers, with the increase in laser power density to 9.15 W/mm², exhibited an increasing luminous flux (23.83–70.26 lm) and maintained a stable luminous efficacy (47.7–46.8 lm/W), and the temperature distribution of the ceramic remained uniform and stable under long-time laser irradiation. This indicates that the nepheline-phase NaAlSiO₄:Eu²⁺ ceramic is a promising material for laser illumination.     

Broadband excited Na3Tb(PO4)2:Ce3+/Eu2+ green/yellow-emitting phosphors with high color purity for LED-based application

To enhance the display quality of light-emitting diodes (LEDs), it is of great significance to exploit green/yellow-emitting phosphors with narrow emission band, high quantum yield, and excellent color purity to satisfy the application. Herein, orthophosphate-based green/yellow-emitting Na₃Tb(PO₄)₂:Ce³⁺/Eu²⁺ (NTPO:Ce³⁺/Eu²⁺) phosphors have been successfully synthesized by a facile solid-state reaction method. The absorption band of NTPO samples was extended to the near-ultraviolet region and the absorption efficiency was significantly improved owing to a highly efficient energy transfer from Ce³⁺/Eu²⁺ ion to Tb³⁺ ion in NTPO host certified by time-resolved PL spectra. Upon 300 nm excitation, the NTPO:Ce³⁺ is characterized by ultra-narrow-band green emission of Tb³⁺ with an absolute quantum yield of 94.5%. Unexpectedly, NTPO:Eu²⁺ emits bright yellow light with a color purity of 73% as a result of the blending of green light emission from Tb³⁺ and red light emission from Eu³⁺. The thermal stability has been improved by controlling the stoichiometric ratio of Na⁺. The prototype white LED used yellow-emitting NTPO:Eu²⁺ phosphor has higher color-rendering index (Ra = 83.5), lower correlated color temperature (CCT = 5206 K), and closer CIE color coordinates (0.338, 0.3187) to the standard white point at (0.333, 0.333) than that used green-emitting NTPO:Ce³⁺ phosphor, indicating the addition of the yellow light component improved the Ra of the trichromatic (RGB) materials.     

Tunable colors and applications of Dy3+/Eu3+ co-doped CaO-B2O3-SiO2 glasses

A series of Dy³⁺/Eu³⁺ single- and co-doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt-quenching method. A compact glass structure is obtained by the addition of Dy³⁺/Eu³⁺ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy³⁺/Eu³⁺ fill in the interspaces of glass network and contribute to the conversion of [BO₃] to [BO₄]. Dy³⁺/Eu³⁺ co-doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white-emitting glasses have proved the existence of energy transfer. The average lifetime of Dy³⁺ decreases from 0.251 to 0.165 ms with the increasing Eu³⁺ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy³⁺/Eu³⁺ co-doped glass shifts from cyan to white with increasing excitation wavelength. A white-light emission is obtained when the concentration of Dy³⁺ and Eu³⁺ equals to 4% and 2%, respectively. Moreover, the Dy³⁺/Eu³⁺ co-doped calcium borosilicate glass shows high-thermal stability and it may be applicable for high-quality white LEDs based on high power near ultraviolet (n-UV) LED chip in the future.     

Investigation of optical properties: Eu with Al codoping in aluminum silicate glasses and glass‐ceramics

Eu‐doped transparent oxyfluoride aluminosilicate glass was prepared by controlling with Al codoping of melt‐quenched glass fabricated under air atmosphere. In the presence of Al input, the photoluminescence emission spectra under 393 nm excitation shows a blue shift by adjusting the ratio of Eu³⁺ and Eu²⁺. After heat treatment of glass, the ratio of Eu³⁺ and Eu²⁺ of luminescence emission were changed by controlling treatment temperature. The PL intensity of Eu³⁺ and Eu²⁺ ions in the glass‐ceramics (GC) was much stronger than in the precursor glass (PG). The possible mechanism responsible for color tuneability of the ratio of Eu³⁺ and Eu²⁺ doped was discussed.     

Fabrication and Characterization of Transparent (Y0.98−xTb0.02Eux)2O3 Ceramics with Color‐Tailorable Emission

Transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ (x = 0–0.04) ceramics with color‐tailorable emission have been successfully fabricated by vacuum sintering at the relatively low temperature of 1700°C for 4 h. These ceramics have the in‐line transmittances of ~73%–76% at 613 nm, the wavelength of Eu³⁺ emission (the ⁵D₀→⁷F₂ transition). Thermodynamic calculation indicates that the Tb⁴⁺ ions in the starting oxide powder can essentially be reduced to Tb³⁺ under ~10^?3 Pa (the pressure for vacuum sintering) when the temperature is above ~394°C. The photoluminescence excitation (PLE) spectra of the transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics exhibit one spin‐forbidden (high‐spin, HS) band at ~323 nm and two spin‐allowed (low‐spin, LS) bands at ~303 and 281 nm. Improved emissions were observed for both Eu³⁺ and Tb³⁺ by varying the excitation wavelength from 270 to 323 nm, without notably changing the color coordinates of the whole emission. The transparent (Y_0.98Tb_0.02)₂O₃ ceramic exhibits the typical green emission of Tb³⁺ at 544 nm (the ⁵D₄→⁷F₅ transition). With increasing Eu³⁺ incorporation, the emission color of the (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics can be precisely tailored from yellowish‐green to reddish‐orange via the effective energy transfer from Tb³⁺ to Eu³⁺ under the excitation with the peak wavelength of the HS band. At the maximum Eu³⁺ emission intensity (x = 0.02), the ceramic shows a high energy‐transfer efficiency of ~85.3%. The fluorescence lifetimes of both the 544 nm Tb³⁺ and 613 nm Eu³⁺ emissions were found to decrease with increasing Eu³⁺ concentration.     

Preparation and luminescence properties of Eu2O3 doped glass-ceramics containing NaY(MoO4)2

Eu₂O₃ doped transparent glass-ceramics containing NaY(MoO₄)₂ crystalline phase were prepared via melting-crystallization. The optimum heat treatment condition (660℃/3h) was determined by DSC, XRD, SEM and transmittance curves. The transmittance of glass-ceramic can reach 80 % in the visible region. The emission spectra of Eu₂O₃ doped glass-ceramics consist of Eu³⁺ ions characteristic emission peaks at 591nm (⁵D₀→⁷F₁) and 614nm (⁵D₀→⁷F₂). The optimal doping concentration of Eu₂O₃ in the glass-ceramics is 0.9 mol%, and fluorescence lifetime is 1.37042ms. The change of the ratio of red emission intensity to orange emission intensity leads to the shift of chromaticity coordinates from orange to red region, and the chromaticity coordinate (0.6337, 0.3635) of 0.9 mol% Eu₂O₃ doped glass-ceramic is closest to the standard red light coordinate. The results show that this kind of glass-ceramic is expected to be good red emission material.     

Structural characterization,energy transfer,and Judd–Ofelt analysis of pure and the Eu3+-doped Ca2LiMg2V3O12 phosphors

A novel vanadate host Ca₂LiMg₂V₃O₁₂ (CLMV) and the Eu³⁺-doped samples were synthesized via a solid-state reaction method. The phase formation and the morphological analysis were studied in detail. The Rietveld refinement result shows that the host belongs to cubic space group Ia-3d (230) with lattice parameter, a = 12.3948 Å, V = 1904.23 Å³, and Z = 8. The diffuse reflectance spectroscopy measurement estimated the bandgap of the host and the CLMV:0.05Eu³⁺ phosphors. The host exhibits a broad absorption band (peak at 345 nm) ranging from 240 to 380 nm, which is attributed to the charge transfer in the O²⁻–V⁵⁺ complex. Under near UV excitation (λ_exc = 345 nm), the host gives a broad emission band covering the visible region from 400 to 730 nm and the emission is in the bluish–green region of the CIE diagram. When the host is doped with the Eu³⁺ ions and excited at 345 nm, the emission spectrum depicts the superimposition of the characteristic emission bands (red emission) of the Eu³⁺ ions corresponding to the f–f transitions over the broad emission band of the host. The calculated color coordinates (9600 to 2280 K) demonstrated the color tuning ability of the phosphor as the dopant concentration is increased in the host. This is because the VO₄³⁻ group plays the sensitiser role and partially transfers energy with the Eu³⁺ ions. When the same set of phosphors were excited at the dominant characteristic excitation band (λ_exc = 394 nm) of the Eu³⁺, the characteristic emission bands of the Eu³⁺ in the orange–red region were observed. As the electric dipole transition of the Eu³⁺ was found to be dominant, the prepared phosphors possessed high color purity (CP). The energy transfer mechanism and the lifetime values were also presented. The temperature-dependent PL studies showed good thermal stability of the optimum sample. Various radiative transition properties were analyzed by the Judd–Ofelt theory. The photometric results reveal the color tuning ability and CP of the CLMV:xEu³⁺ phosphors.     

Intense red emission via energy transfer from (Ce3+/Eu3+):P2O5+NaF+CaF2+AlF3 glasses for warm light sources

Europium (Eu³⁺)-doped fluorophosphate (PNCA:P₂O₅+NaF + CaF₂+AlF₃) glasses with the addition of cerium (Ce³⁺) ions were fabricated by the melt-quenching technique to know their ability for the bright red (615 nm) luminescence. The emission (PL) and excitation (PLE) spectra, decay curve measurements as well as energy transfer (ET) process of Ce³⁺→ Eu³⁺ were studied in detail. An excitation spectrum related to the ⁷F₀→ ⁵D₂ level of Eu³⁺ is used to estimate the phonon energy (1121 cm^?1) of the title glass host. Under ultraviolet (UV) irradiation of 299 nm, the PL spectra of (Ce³⁺/Eu³⁺):PNCA glasses show intense red emission at 615 nm whereas the lifetime decrease with respect to increase of Eu³⁺ that could support the observed efficient ET from Ce³⁺ to Eu³⁺. The ET:Ce³⁺ →Eu³⁺ via quadrupole-quadrupole process was confirmed by Reisfeld's approximation and Dexter's ET formula. The ET efficiency (η_ET) and critical distance (R_c) were also calculated. Interestingly, the (Ce³⁺/Eu³⁺):PNCA glasses showed intense red light emission with low correlated color temperatures and the corresponding color purity reached as great as 99%, indicating its potentiality as a red component for warm light sources.     

Eu3+‐doped glass as a color rendering index enhancer in phosphor‐in‐glass

A new method for improving color rendering index (CRI) and low correlated color temperature (CCT) in high‐power white‐light‐emitting diodes (WLEDs) is proposed. We used a configuration of phosphor‐in‐glass (PIG) and studied light output changes with the increment in concentration of yellow‐emitting Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) phosphor. The PIG was coupled on the top of blue‐light‐emitting diodes (LED) chip (465 nm). To compensate the lack of red emission in the phosphor, Eu³⁺‐doped tellurium glass with different europium content was employed as a red emitter. The suitable contents of YAG:Ce³⁺ and Eu³⁺ were 7.5 weight percent (wt%) and 3 mol percent (mol%), respectively. The CRI value went from 72 to 82, whereas the CCT was reduced from 24 933 to 6434 K. The proposed structure can improve CCT as well as CRI of WLEDs just by placing a glass on top.     

Study of Eu3+–Gd3+ co-doped Ba–Bi–B glasses for red-laser applications: Physical,structural, photoluminescence and time-resolved spectral characteristics

A series of Eu³⁺ and Eu³⁺/Gd³⁺ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd³⁺ to Eu³⁺ ions. The density of glasses increased with increasing of Gd³⁺ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu³⁺-Gd³⁺ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu³⁺: ⁵D₀→ ⁷F₂ transition. Less intense emissions centered at 577 nm (⁷F₀), 590 nm (⁷F₁), 651 nm (⁷F₃) and 700 nm (⁷F₄) are also observed from the radiative transitions of the excited state ⁵D₀ of Eu³⁺ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu³⁺ and 3.0 mol% Gd³⁺ co-doped glass under λ_Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications.     

Energy transfer,tunable emission and optical thermometry in Tb3+/Eu3+ co-doped transparent NaCaPO4 glass ceramics

Tb³⁺/Eu³⁺ co-doped glass ceramics containing NaCaPO₄ nanocrystals were successfully synthesized via traditional melt-quenching route with further heat-treatment and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy. The energy transfer process of Tb³⁺→Eu³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results indicated that the efficient emission of Eu³⁺ was sensitized by Tb³⁺ under the excitation of 378 nm, realizing tunable emission in the transparent bulk glass ceramics containing NaCaPO₄ nanocrystals. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺:⁵D₄→⁷F₅ (~542 nm) and Eu³⁺:⁵D₀→⁷F₂ (~612 nm). The maximum absolute sensitivity of 4.55% K⁻¹ at 293 K and the maximal relative sensitivity of 0.66% K⁻¹ at T=573 K for Tb³⁺/Eu³⁺ co-doped transparent NaCaPO₄ glass ceramic are obtained. It is expected that the investigated transparent NaCaPO₄ glass ceramics doped with Tb³⁺/Eu³⁺ have prospective applications in display technology and optical thermometry.     

Warm-white light performance of Dy3+, Eu3+: NaLa(WO4)2 phosphors excited with a 450-nm LED

Dy³⁺, Eu³⁺: NaLa(WO₄)₂ phosphors are successfully synthesized through the solid-state reaction technique. The phase-structure and morphology are measured via X-ray diffraction and energy dispersive spectrometry. The concentrations of Dy³⁺, Eu³⁺, La³⁺, and W⁶⁺ are measured via ICP. The absorption and excited spectra are presented, which indicate that a blue band ranging from 430 to 480 nm is suitable for excitation. Using a commercial blue LED with a wavelength of 450 nm as the excitation light source, emission spectra for samples with varying dopant concentration ratios of Dy³⁺ to Eu³⁺ are obtained, which show good tunable yellow and red emission. For the purpose of investigating white LED performance, CIE spectra and a white light photo are also presented. The results reveal that varying the dopant concentration ratio of Dy³⁺ to Eu³⁺ plays a key role in the warm-white performance. With increasing concentration of Eu³⁺, the correlated color temperature decreases from 4069 to 3172 K, which indicates good warm-white performance.     

Design of Eu2+-activated broadband orange-emitting phosphors with excellent luminescent performance for warm WLEDs

We report orange-emitting Sr₈La_0.5Na_0.5Mg_1.5(PO₄)₇:Eu²⁺ (SLNMPO-0.5:Eu²⁺) and Sr₇LaNaMg_1.5(PO₄)₇:Eu²⁺ (SLNMPO-1:Eu²⁺) phosphors with broad emission bands covering from 450 to 800 nm. The phosphors can be excited by n-ultraviolet and blue light efficiently. Their crystal structure, diffuse reflection spectra, photoluminescence (PL) spectra, fluorescence decay curves and thermal stability were investigated systematically. Under the excitation of 365 and 400 nm, SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ both exhibit better PL properties and contain more red emissions than SMPO:Eu²⁺. CIE coordinates of SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ under 365 nm excitation are (0.460, 0.497) and (0.457, 0.494), respectively. Furthermore, high-quality warm white light can be generated by fabricating warm white light-emitting diode (WLED) devices with 370 nm LED chips, BaMgAl₁₀O₁₇:Eu²⁺ commercial blue phosphor and orange-emitting SLNMPO-0.5:Eu²⁺ (or SLNMPO-1:Eu²⁺) phosphor. The correlated color temperature, R_a and color coordinates are 3880 K, 94.05, (0.3895, 0.3922) and 3736 K, 91.73, (0.4005, 0.4078) for the fabricated WLED devices with SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺, respectively. The excellent performances indicate that SLNMPO-0.5:Eu²⁺ and SLNMPO-1:Eu²⁺ have great potential to be attractive candidates in the application of warm WLEDs.