Tricolor Phosphors Research Articles

Interrupting the long-range energy migration among Eu3+ by the introduction of unequivalent [NaO8] units to achieve both high quenching concentration and quantum yield in NaY2Ga2InGe2O12

In the pursuit of optimizing white light-emitting diodes (WLEDs), Eu3+-doped phosphors have emerged as a key component in strategies that combine ultraviolet (UV) LED chips with red, green, and blue (RGB) tricolor phosphors. However, their application has been notably constrained by concentration quenching and thermal quenching. To address this challenge, we have developed a series of novel red phosphors, NaY2-xGa2InGe2O12:xEu3+. The powder X-ray diffraction (XRD) indicates that the NaY2Ga2InGe2O12(NYGIG) belongs to the garnet family. The [NaO8] unit replaces one-third of the eight-coordinated sites of garnet and leaves the other two-thirds for the [YO8], which helps to prevent long-range energy migration among Eu3+ especially when the eight-coordinated sites were highly substituted. Such a structure feature allowed the NaY2-xGa2InGe2O12:xEu3+ phosphor to achieve an optimal quantum yield of 95.6% at an extremely high Eu3+ doping x value up to 1.2. Moreover, further studies on the temperature-dependent luminescence spectra confirm that an anomalous thermal quenching phenomenon will occur when the NaY2-xGa2InGe2O12:1.2Eu3+ phosphor is properly excited. In application, the combination of the red-emitting NaY2-xGa2InGe2O12:1.2Eu3+, blue-emitting BaMgAl10O17:Eu2+, and green-emitting Zn2SiO4:Mn2+ phosphors can realize high color rendering (CRI∼93) white light with the with CIE coordinates of (0.353,0.350), indicating that the NYGIG:Eu3+ phosphor own a promising potential for WLEDs.

Efficient White Light‐Emitting Diodes Based on Cu(I) Activated Single‐Phase Halide Single Crystals

Single‐phase white light emitters have become a potential substitute for tricolor phosphor mixtures for the white light‐emitting diodes (WLEDs) application to simplify device structure and eliminate self‐absorption. Newly developed low‐dimensional halides, noted for their highly efficient luminescent characteristics, have seen increasing interest in recent years. Herein, highly efficient white‐light emission is demonstrated in single‐phase zero‐dimensional halide single crystal, namely monovalent Cu‐doped Cs2HfCl6. Cs2HfCl6:Cu single crystals have three luminescent centers. Two emission peaks at 365 nm and 380 nm correspond to the intrinsic self‐trapped excitons emission and a defect‐related trapped exciton emission, respectively. Cu doping introduces an intense Cu‐bound exciton emission peaking at 540 nm with a large Stokes shift of 250 nm and a high photoluminescence quantum yield of 68%. With different excitation wavelengths and Cu‐doping concentrations, Cs2HfCl6:Cu single crystals show tunable emissions. Under 254 nm ultraviolet light excitation, Cs2HfCl6:0.5%Cu yields cold white light with a high color rendering index (Ra = 87.3). These findings demonstrate the potential of Cs2HfCl6:Cu as a promising phosphor for cold WLEDs.

Separation and enrichment of tricolor phosphors in waste phosphors through liquid–liquid–powder extraction method and its benefit evaluation for recovery

This study aimed to separate and enrich tricolor phosphors powder including red, blue, and green phosphors in waste phosphors which also contained white phosphors through liquid–liquid–powder extraction method. Kerosene and water were used as the two liquids. Dodecylamine acetate (DAA) was used as the surfactant collector. The operating factors including pH, DAA dosage, kerosene–water volume ratio, solid concentration, extraction temperature, and extraction time, on the enrichment of tricolor phosphors powder were investigated. In addition, the benefit of introducing liquid–liquid–powder extraction method in the recovery procedure of tricolor phosphors from waste phosphors was also evaluated through the comparison of applying hydrochloric acid (HCl) leaching for the separated tricolor phosphors and the waste phosphors.The results indicated that the optimal conditions of liquid–liquid–powder extraction method were that the dosage of DAA was 1.5 kg/ton at pH 3 with a kerosene–water volume ratio of 20/80 (v/v), a solid concentration of 1.25 w/v%, an extraction temperature of 25 °C, and an extraction time of 15 mins. Under these conditions, the grade of tricolor phosphors recovered from the water phase was enriched from its initial grade of 15.0 % in the waste phosphors to 72.5 % with a recovery of 67.4 %. The benefit of introducing liquid–liquid–powder extraction method was that more than 50 % of the reagent cost and nearly 90 % of the wastewater generation were reduced compared to those without liquid–liquid–powder extraction treatment. In addition, white phosphors with a grade of 92.3 % and a recovery of 96.7 % could be recovered from the kerosene phase simultaneously. This study also demonstrates the merit of introducing a physical separation treatment in a resources recovery procedure before chemical treatment.

A single-phase Ca2GdNbO6: Dy3+ white light-emitting phosphors for near-UV double-excited WLEDs application

The development of white light emitting diodes (WLEDs) prepared with tricolor phosphors is limited by issues such as reabsorption, difficulty in controlling sample proportions, low thermal stability, etc. This study synthesized a series of single-host Ca2GdNbO6:xDy3+ (CGNO:xDy3+) phosphors using High-temperature Solid-state Reaction. Then the structure characteristics, luminescence, thermal stability, and morphology were analyzed in detail. The results showed that all the samples, emitted white light superposed by the blue at 483 nm and the yellow light at 575 nm under near-ultraviolet excitation, exhibit good quantum yield, excellent optical properties, and good moisture resistance. Besides, the CIE chromaticity coordinates (CIE) and luminous pictures of CGNO:xDy3+ phosphors both at 352 nm and 389 nm were investigated. Then, the properties of LED devices obtained by coating the aforementioned phosphors on 365 nm and 395 nm chips were characterized. The research confirmed that CGNO:xDy3+ are potential single-host white light phosphors in the field of lighting.

Wide-band blue-emitting in Ce3+ doped Ca2YZr2Al3O12 garnet-type phosphor designed via local structural lattice distortion and synthesized in nonreducing atmosphere

It is of great significance to explore blue photoluminescent phosphor for white light-emitting diodes excited by near-ultraviolet chip. However, it is very challenging to prepare efficient blue luminescence in phosphor by an unsophisticated synthesis process. In this work, a series of blue-emitting Ca 2 Y 1-x Zr 2 Al 3 O 12 : xCe 3+ phosphors are designed via local lattice distortion and synthesized in nonreducing atmosphere. The crystal structure of samples and the coordination environment of Ce 3+ have been investigated in detail by X-ray diffraction and Rietveld refinement method. The wide-band blue emission peaking at 460 nm is attributed to a relaxed crystal field strength. Based on dodecahedron distortion caused by unequal increase of Ce–O bond length, the wavelength of blue color luminescence tuning can be realized from 459 nm to 472 nm. In addition to the concentration quenching effect, the fluorescent lifetimes, thermal quenching effect, the internal quantum efficiency, CIE chromaticity coordinates and related mechanisms of samples have also been studied systematically. Using the representative sample with other tricolor phosphors on a 365 nm chip, a prototype LED device with chromaticity point of (0.394, 0.384) and high CRI (93.5) at CCT of 3755 K is fabricated. All the results suggest that Ca 2 Y 1-x Zr 2 Al 3 O 12 : xCe 3+ phosphors can be conducted as potential alternative of blue-emitting phosphor for near-ultraviolet pumped white light-emitting diodes.

Fabrication of W-LEDs by Coating Tri-Color Inorganic Phosphors on UV-Diode

YAG:Ce phosphor coated on blue-chip gives many advantages, except the color rendering of the LEDs fabricated by this method is poor due to the lack of red and green colors. This problem can be sorted out by choosing different methods out of the available two different methods. For the first method, the n-UV (near-ultraviolet) LED is coated with a mixture of intense blue, green, and red phosphors to make a white light-emitting diode. Also, if the yellow color phosphor is added, lamps can give better CRI values. So many papers are reported on this type of white LED fabrication technique. In this paper, we have reported the fabrication of white LED lamps by coating three different phosphors i.e. blue, green, and red in the appropriate amount to be mixed and coated on the near UV LED chips. This approach is different from the existing reports because we are using near UV (405-407 nm LEDs) not the UV LED chips in the fabrication of white LEDs in this paper.

Novel near-ultraviolet-excited and thermally-stable blue-emitting phosphor for healthy WLED lighting

The widespread popularity of white light-emitting diodes (WLED) lighting results in a chronic exposure to blue light, which has negative impacts on human biological functions, emotions and health. As an alternative strategy, integrating near-ultraviolet (n-UV) LED chips with high-efficiency (high quantum efficiency, chemical and thermal stability) tricolor phosphors, can easily achieve high-quality white light and diminish the so-called “blue-light hazard”. However, few blue-emitting phosphors can meet the aforementioned requirements. Herein, we report a novel n-UV excited bright blue-emitting CsBaB9O15:2%Eu2+ phosphor with high internal quantum efficiency (IQE = 68.8%) and outstanding thermal stability (94.2%@ 150 °C, 84%@ 250 °C). Impressively, this phosphor exhibits excellent chromaticity stability (Δx = 0.002, Δy = 0.012; 3.6 × 10−3 ≤ ΔE ≤ 8.1 × 10−3) from 25 to 150 °C. These remarkable thermal stability are mainly ascribed to the large band gap of host (Eg = 5.85 eV), which effectively suppresses the thermal ionization pathway of the dominant 440 nm emission in the CsBaB9O15:2%Eu2+ phosphor. A WLED device was fabricated by combining commercial phosphor Sr2Si5N8:Eu2+, green phosphor (Sr, Ba)2SiO4:Eu2+ and as-synthesized blue phosphor with a 380 nm n-UV LED chip, which exhibits high color-rendering index (CRI = 90) and low correlated color temperature (CCT = 3301 K). These results demonstrate that the outstanding CsBaB9O15:Eu2+ blue phosphor could be a candidate for next-generation healthy WLED lighting.

Multiple Charge Transfer Bands Induced Broad Excitation Eu3+ Red Emission in a Vanadium Phosphate System for White Light-Emitting Diodes.

In order to realize broad excitation and narrow emission red light phosphor, a new vanadium phosphate Ba2BiV2PO11 was selected as a host for Eu3+. Monitored at 619 nm, a wide band from 240 to 400 nm could be observed and inferred to be composed of Eu3+-O2- and V5+-O2- charge transfer bands, which could make it match well with the UV chip and the blue chip along with the characteristic excitation of Eu3+ at 465 nm. Under 354 nm excitation, the sample could emit high color purity red light, and the thermal quenching integral intensity showed good thermal stability. The generation of charge transfer bands was investigated in detail combined with the luminescence properties and the structure of the matrix. Moreover, the as-prepared phosphor could improve the white light performance of blue chip-activated YAG:Ce3+ and n-UV chip-activated tricolor phosphors. All the results indicated the multiple application potential of Ba2BiV2PO11:Eu3+ for white light-emitting diodes.

Emerging near-unity internal quantum efficiency and color purity from red-emitting phosphors for warm white LED with enhanced color rendition

A robust and bright red emitter is recognized as a key enabler for high-quality warm white light-emitting diode (w-LED). Herein, triple molybdate scheelite-type NaCaLa1-x(MoO4)3:xEu3+ (NCLM:xEu3+) phosphors derived from NaCaLa(MoO4)3 host by the equivalent-valent substitution strategy are successfully synthesized and systematically studied. Impressively, the NCLM:Eu3+ phosphors (λem = 615 nm) can be effectively stimulated by 395 and 466 nm light, exhibiting an ultra-high color purity and quantum efficiency close to 100%. The structure-related emission characteristics were analyzed based on the Judd-Oflet theory. The packaged white LED device used tri-color phosphors displays a superior color rendering index of 86.0 and low correlated color temperature of 2797 K. Moreover, the NCLM-based polydimethylsiloxane film maintains an impressive luminescent performance when it is folded or bent, demonstrating the potential applications in the field of flexible display and other light-emitting devices.

High-brightness cyan-emitting Eu2+-activated orthophosphate phosphors for near-UV-pumped white LEDs

Near-ultraviolet (near-UV) pumped white light-emitting diodes (w-LEDs) based on tri-color (blue/green/red) phosphors have been regarded as an important approach to realize high-quality solid-state lighting, but the cyan gap between the blue and green phosphors imposes a limitation on the color rendering index. To solve this problem, efficient cyan phosphors with emission peaking around 490 nm and broad absorption band in the near-ultraviolet range are urgently needed. Herein, we demonstrate an efficient near-UV-excitable cyan-emitting LiBaPO4:Eu2+ orthophosphate phosphor for high-color-rendering w-LEDs. The prepared LiBaPO4:Eu2+ phosphors show a broad excitation band in the wavelength range of 250–450 nm peaking at 353 nm. Under 353 nm excitation, LiBaPO4:Eu2+ phosphors produce a wide cyan emission band in the wavelength range of 400–700 nm with a peak about 485 nm and bandwidth of 99 nm. More importantly, LiBaPO4:Eu2+ phosphors exhibit a high internal quantum efficiency of 88.3%. A w-LED device is fabricated with a 365 nm near-UV LED chip with LiBaPO4:Eu2+ cyan phosphors and commercial CaAlSiN3:Eu2+ red phosphors, which demonstrates bright white emission with a color rendering index of 84.2 and correlated color temperature of 5243 K.

Using an excellent near-UV-excited cyan-emitting phosphor for enhancing the color rendering index of warm-white LEDs by filling the cyan gap

White light-emitting diodes (LEDs) with high color rendering index (CRI) and low correlated color temperature (CCT) are desirable for next-generation solid-state lighting. In this work, we demonstrated an efficient near-UV-excited cyan-emitting phosphor based on Ce3+-doped Ca2LuHf2Al3O12 (CLHAO) garnet, which could be used to cover the cyan gap for fabricating high-CRI warm-white LEDs. We found that the CLHAO:Ce3+ samples exhibited a broad excitation band in the 300–450 nm wavelength range peaking at 400 nm, and upon 400 nm excitation they showed broad cyan emission bands in the 420–600 nm spectral region with peak positions ranging from 477 to 493 nm. The optimal CLHAO:0.02Ce3+ sample had CIE color coordinates of (0.160, 0.255), and its internal and external quantum efficiencies were measured to be 84.3% and 60.8%, respectively. Impressively, the luminescence intensity of CLHAO:0.02Ce3+ sample at 423 K still remained at 62% of the initial value at 303 K, and the chromaticity shift was calculated to be as low as 1.7 × 10−2, revealing its high thermal stability and color stability at a higher temperature. Finally, a warm-white LED device (CCT = 3,194 K) was fabricated by combining CLHAO:0.02Ce3+ cyan phosphors with commercial blue/green/red tricolor phosphors, showing bright white-light emission with a high CRI of 89.4, which was superior to that of another warm-white LED device (CRI = 83.2) fabricated without CLHAO:0.02Ce3+ cyan phosphors. These outstanding luminescence properties of CLHAO:Ce3+ cyan phosphors illustrated that they offer a new feasible approach for the production of high-CRI warm-white LEDs toward high-color-quality solid-state lighting.

Insight into the crystal structure and photoluminescence properties of an extremely broadband yellow-emitting phosphor Sr8MgCe(PO4)7:Eu2.

The combination of binary complementary color phosphors with near-ultraviolet (NUV) light-emitting diode (LED) chips was put forward to lower the energy loss caused by the reabsorption of the combination of tricolor phosphors with NUV LED chips. Thus investigating broadband yellow-emitting phosphors with enriched red components in the spectral range has gained much attention. Here, an extremely broadband yellow-emitting phosphor Sr8MgCe(PO4)7:Eu2+ with sufficient red component in the spectral region was synthesized. Due to the introduction of Ce into the host, Sr8MgCe(PO4)7 shows an emission band with a peak at 375 nm when excited at 310 nm. Meanwhile, Eu2+ doped Sr8MgCe(PO4)7 exhibits an extremely broad yellow emission band with a full width at half-maximum of 175 nm and a peak located at about 598 nm, due to the 5d-4f transitions of Eu2+ ions substituting five Sr2+ sites. The excitation peak of the host at 310 nm was detected in the excitation spectrum of Sr8MgCe(PO4)7:Eu2+ monitored at 598 nm, indicating the energy transfer from the host to Eu2+, which was also proved by the decay curves. On the other hand, the excitation band at about 400 nm due to the 4f-5d transitions of Eu2+ was also detected in the excitation spectrum of Sr8MgCe(PO4)7:Eu2+, and this matches well with the NUV LED chips. Moreover, the energy transfer between Eu2+ ions at different crystallographic sites was demonstrated by time-resolved photoluminescence (TRPL) spectra. A white LED with a CRI (Ra) of 82.88 and a CCT of 4238 K was prepared through a 400 nm NUV LED chip, Sr8MgCe(PO4)7:Eu2+ and BaMgAl10O17:Eu2+ (BAM:Eu2+). These results pave the way for designing better Eu2+-doped phosphors for NUV WLEDs with binary complementary color phosphors.

Enhanced photoluminescence in a Eu3+ doped CaTiO3 perovskite phosphor via incorporation of alkali ions for white LEDs

Intense red photoluminescence has been observed in Eu3+/Z+ (Z+ = Li+, Na+ & K+) co-doped CaTiO3 perovskite phosphor materials, synthesized through high temperature solid-state reaction technique. The phosphor materials are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. All the compounds are crystalline with the orthorhombic phase. The crystallite and particle size of phosphor increase via incorporation of alkali ions. The vibrational groups in phosphor materials are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra showed a number of peaks in the UV–visible regions due to different transitions of Eu3+ ion. The band gap (Eg) of the phosphor decreases on incorporation of alkali ions. The phosphor materials emit intense red color at 613 nm due to 5D0 → 7F2 transition of Eu3+ ion upon 398 nm and 466 nm excitation wavelengths. The intensity of red emission increases upto 12 mol% concentration of Eu3+ ions. On incorporation of alkali ions in the 12 mol% Eu3+: CaTiO3 phosphor, the emission intensity increases further due to crystallinity, charge compensation and the asymmetry created around the Eu3+ ions in the phosphor. The emission intensity is largest for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The asymmetric ratio is higher for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The lifetime of 5D0 level is enhanced via incorporation of alkali ions and it is also larger for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The CIE color coordinates, correlated color temperature (CCT), color purity and color rendering index (CRI) calculations of the phosphors have also been carried out, which show pure red color in warm light region. Therefore, these synthesized perovskite phosphor materials can be advantageous for display devices, NUV excited red phosphors for making the tricolor phosphor converted WLEDs and blue LED chip-based WLEDs for solid state lighting applications.

Ultra-high color rendering warm-white light-emitting diodes based on an efficient green-emitting garnet phosphor for solid-state lighting

High light-quality and low color temperature are two crucial factors for a comfortable healthy illumination. Phosphor-converted white light-emitting diodes (LEDs) could be readily realized by combining near-UV (380–420 nm) LED chips with tri-color phosphors, and thus near-UV-excitable inorganic phosphors with efficient visible luminescence are highly demanded for fabricating high-performance near-UV-pumped white LEDs. Herein, we demonstrated a novel highly efficient green-emitting phosphor based on Ce3+/Tb3+ ions co-activated Ca2GdHf2Al3O12 (abbreviated as: CGHAO) garnet compound, which enabled the realization of ultra-high color rendering warm-white LEDs. Notably, the CGHAO:Ce3+,Tb3+ phosphors could be efficiently excited by near-UV light around 408 nm and exhibited intense green emissions around 543 nm with high internal quantum efficiency of 82.7% and external quantum efficiency of 60.6%. The energy transfer from Ce3+ to Tb3+ ions was studied in detail, and the composition of CGHAO:Ce3+,Tb3+ phosphors was optimized. Utilizing the optimal CGHAO:0.04Ce3+,0.4Tb3+ green phosphor as color converter, a prototype near-UV-pumped white LED device was fabricated, and upon 120 mA driving current it demonstrated bright warm-white light with excellent CIE chromaticity coordinates of (0.391, 0.360), low correlated color temperature of 3575 K, ultra-high color rendering index (Ra = 94.4, R12 = 89.0, and R9 = 80.6) and good luminous efficacy of 27.40 lm·W−1. This work offers a new strategy for designing efficient LED phosphors for high-color-quality solid-state lighting.

Achieving full-visible-spectrum LED lighting via employing an efficient Ce3+-activated cyan phosphor

At present, near-ultraviolet-pumped white light-emitting diodes (LEDs) based on tri-color (blue, green, and red) phosphors still suffer from insufficient color rendering index (CRI), due to the presence of cyan gap in the 480–520 nm spectral range. To solve this problem, it is urgent to develop an efficient cyan phosphor with emission peak around 490 nm and absorption band in the near-ultraviolet range of 380–420 nm. Herein, a highly efficient cyan-emitting Ca2GdHf2(AlO4)3:Ce3+ (CGHA:Ce3+) garnet phosphor with internal quantum efficiency as great as 80% is reported. Impressively, the CGHA:1%Ce3+ sample showed a broad excitation band ranging from 350 to 470 nm with a maximum at 408 nm, and upon 408 nm excitation it exhibited an intense broad cyan emission band in the 420–700 nm wavelength range with peak at 489 nm and a full width at half-maximum of 103 nm. Importantly, by applying the newly discovered cyan-emitting CGHA:1%Ce3+ phosphors as color converter, the CRI value of the fabricated warm-white LED device is greatly enhanced from 80.5 to 91.6. This work demonstrates that the novel developed CGHA:Ce3+ cyan phosphors could compensate for the cyan gap and realize full-visible-spectrum lighting, which have a bright prospect in high-quality solid-state white lighting.

Single 395 nm excitation warm WLED with a luminous efficiency of 10486 lm/W and a color rendering index of 907

A blue Sr5(PO4)3Cl:Eu2+ phosphor was synthesized by the solid state reaction method. Higher luminescence intensity was observed by increasing the NH4Cl content to twice the stoichiometric ratio. Then a near UV excited warm white LED was fabricated by using an InGaN/GaN chip (395 nm) coated with tricolor phosphors, including (Sr,Ca)AlSiN3: Eu2+ (red), (Ba,Sr)2SiO4: Eu2+ (green), and Sr5(PO4)3Cl:Eu2+ (blue). Moreover, a two-layer LED fabrication structure was designed to weaken the secondary absorption of blue emission by the red and green phosphors. A good luminescence performance was achieved with the correlated color temperature (CCT) of 3150 K, a color rendering index (CRI) of 90.7, CIE chromatic coordinates of (0.4354, 0.4196), and luminous efficiency of 104.86lm/W.

A terbium activated multicolour photoluminescent phosphor for luminescent anticounterfeiting

The multicolor photoluminescence (PL) of a Tb3+ singly activated NaYGeO4 phosphor is prepared by solid state method. For the first time, it is reported that the PL color of Tb3+ in NaYGeO4 phosphor can be tuned from green to blue and, finally, to red by controlling the Tb3+ content. The optimal tricolor phosphors are NaYGeO4:0.01 mol% Tb3+ (red), NaYGeO4:0.5 mol% Tb3+ (blue) and NaYGeO4:5 mol% Tb3+ (green), respectively. The PL properties of the NaYGeO4:Tb3+ phosphor were studied in details. The results reveal that the PL color modulations of the NaYGeO4:Tb3+ phosphor are essentially due to the cross-relaxation effect of Tb3+, and a possible mechanism on the cross-relaxation is proposed. According to these unique features, a multicolor PL image was fabricated based on the NaYGeO4:Tb3+ phosphor for potential applications in luminescent anticounterfeiting.

Near ultraviolet excited white light emitting diode (WLED) based on the blue LiCaPO4:Eu2+ phosphor

One near ultraviolet (NUV) chip coated with tricolor phosphors to fabricate the white light emitting diode (WLED) has been attractive widely. In this paper, the blue emitting LiCaPO4:Eu2+, together with the red CaSiAlN3: Eu2+ and the green (Sr, Ba)SiO4: Eu2+ phosphor, is selected as the tricolor components for the NUV excited WLED preparation. The as-prepared WLED exhibits good luminescent performances with the color rendering index (Ra) of 88.6, the correlation color temperature of 3351 K, the lumen efficiency of 77.05 lm/W, and the color coordinates located at (0.4399, 0.4389). It is worth mentioning that the blue-light of the warm WLED succeeds to keep away from the hazard zone centered at 450 nm. Furthermore, a full spectrum warm WLED with the color rendering index (CRI) of 95.8 is fabricated by adding the fourth component as the Sr5(PO4)3Cl:Eu2+ phosphor. The prepared full spectrum WLED achieves the performance index of museum lighting.

Facile fabrication of thermal stable Eu(HCOO)3 red-emitting crystals with high color purity for near-ultraviolet chip triggered white light-emitting diodes

The thermal stable Eu(HCOO)3 red-emitting crystals were synthesized by a facile hydrothermal route. Both excitation and emission spectra revealed that the prepared crystals can be efficiently pumped by the near-ultraviolet (NUV) light and it can emit brightness red light with admirable color purity of 90.4%. With the help of Judd-Ofelt theory, the optical transition intensity parameters of Eu3+ ions were evaluated so as to explore its local symmetry performance in the Eu(HCOO)3 host lattices. The thermal quenching behaviors of the studied samples were investigated through the temperature-dependent emission spectra. Ultimately, a white light-emitting diode (WLED) lamp with good color rendering index (78.2) and correlated color temperature (6386 K) was packaged through coating the tricolor phosphors (BaMgAl10O7:Eu2+ blue-emitting phosphor, (Ba,Sr)2SiO4:Eu2+ green-emitting phosphor and resultant red-emitting crystals) onto the surface of a NUV chip. These results disclosed the high brightness Eu(HCOO)3 red-emitting crystals were suitable for NUV chip triggered WLED applications.

Near-ultraviolet excited down-conversion Sm3+-doped Ba5Zn4Gd8O21 reddish-orange emitting nano-diametric rods for white LEDs

Down-conversion Ba5Zn4Gd8O21:Sm3+ reddish-orange nanocrystalline phosphors with high quantum efficiency were well-synthesized by solution combustion route. The structural and morphological characterizations were systematically done via X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Refined atomic positions as well as unit cell parameters for optimum composition were calculated using refinement technique. The results revealed that the substitution of Gd3+ ions by Sm3+ ions in Ba5Zn4Gd7.76Sm0.24O21 nanophosphor did not induce any major structural change and confirmed its tetragonal framework with I4/m (87) space group. TEM studies indicated the rod-shaped morphology with uniform samarium ion distribution of combustion derived nanophosphor ranging from 40 to 90 nm. The energy band-gap values for Ba5Zn4Gd8O21 (5.1 eV) and Ba5Zn4Gd7.76Sm0.24O21 (4.88 eV) were estimated from diffuse reflectance (DR) measurements. Further, the photoluminescence studies upon 410 nm excitation yielded the reddish-orange luminescence (at 610 nm) attributed to 4G5/2→6H7/2 transition of Sm3+ ions. The luminescence intensity of samarium-activated phosphor reached the maximum at the Sm3+ content of 3 mol%, for which the critical separation (RSm-RSm) was ≈ 16.5 Å. In addition, the energy relaxation process in Ba5Zn4Gd8O21:Sm3+ was clearly observed, which was confirmed via electric dipole-quadrupole interaction pathway. Besides, the radiative lifetime (1.19 ms), non-radiative relaxation rate (544.31 s−1) and most importantly, the quantum efficiency of 4G5/2 electronic state (60%) were also analyzed in detail. The obtained CIE chromaticity coordinates favour the applications of samarium activated Ba5Zn4Gd8O21 phosphor in near-ultraviolet (NUV) excited tricolor phosphor based white light-emitting diodes (WLEDs).