A new‐generation color converter for high‐power white LED: transparent Ce3+:YAG phosphor‐in‐glass

Currently, the major commercial white light‐emitting diode (WLED) is the phosphor‐converted LED made of the InGaN blue‐emitting chip and the Ce³⁺:Y₃Al₅O₁₂ (Ce:YAG) yellow phosphor dispersed in organic epoxy resin or silicone. However, the organic binder in high‐power WLED may age easily and turn yellow due to the accumulated heat emitted from the chip, which adversely affects the WLED properties such as luminous efficacy and color coordination, and therefore reduces its long‐term reliability as well as lifetime. Herein, an innovative luminescent material: transparent Ce:YAG phosphor‐in‐glass (PiG) inorganic color converter, is developed to replace the conventional resin/silicone‐based phosphor converter for the construction of high‐power WLED. The PiG‐based WLED exhibits not only excellent heat‐resistance and humidity‐resistance characteristics, but also superior optical performances with a luminous efficacy of 124 lm/W, a correlated color temperature of 6674 K and a color rendering index of 70. This easy fabrication, low‐cost and long‐lifetime WLED is expected to be a new‐generation indoor/outdoor high‐power lighting source.     

Cesium lead halide perovskite quantum dot-based warm white light-emitting diodes with high color rendering index

White light-emitting diodes (WLEDs) were fabricated by employing a combination of a commercial yellow emission Ce³⁺-doped Y₃Al₅O₁₂ (YAG:Ce)-based phosphor and all-inorganic perovskite quantum dots pumped with blue LED chip. Perovskite quantum dot solution was used as the color conversion layer with liquid-type structure. Red-emitting materials based on cesium lead halide (CsPb(X)₃) perovskite quantum dots were introduced to generate WLEDs with high efficacy and high color rendering index through compensating the red emission of the YAG:Ce phosphor-based commercialized WLEDs. The experimental results suggested that the luminous efficiency and color rendering index of the as-prepared WLED device could reach up to 84.7 lm/W and 89, respectively. The characteristics of those devices including correlated color temperature (CCT), color rendering index (CRI), and color coordinates were observed under different forward currents. The as-fabricated warm WLEDs showed excellent color stability against the increasing current, while the color coordinates shifted slightly from (0.3837, 0.3635) at 20 mA to (0.3772, 0.3592) at 120 mA and color temperature tuned from 3803 to 3953 K.     

Origin of the discrepancy between photoluminescence brightness of TAG:Ce and electroluminescence brightness of TAG:Ce-based white LED expected from phosphor brightness

A yellow-emitting Tb(3)Al(5)O(12):Ce(3+) (TAG:Ce) phosphor was coated on blue light-emitting diodes (LEDs) to obtain white LEDs (WLEDs). Since TAG:Ce showed 90% of the brightness of Y(3)Al(5)O(12):Ce(3+) (YAG:Ce), it was expected that TAG:Ce-based WLEDs showed 90% of brightness of YAG:Ce-based ones. However, the TAG:Ce-based WLED showed 74% of the brightness of YAG:Ce-based one. Considering the density and size of the phosphors, the higher density and larger size of TAG:Ce induced a great deal of sedimentation of TAG:Ce particles in an epoxy resin. It is believed that this is one of main reasons for the reduced optical power of the TAG:Ce-based WLED compared to that of the WLED expected from the brightness of TAG:Ce.     

White light emission from blue and near ultraviolet light-emitting diodes precoated with a Sr3SiO5:Ce3+,Li+ phosphor

White-light-emitting diodes (WLEDs) were fabricated by combining a yellow Sr3SiO5:Ce3+, Li+ phosphor with a blue light-emitting diode (LED) (460 nm chip) or a near ultraviolet (n-UV) LED (405 nm chip), respectively. Color temperature (Tc) of Sr3SiO5:Ce3+, Li+-based WLEDs could be tuned from 6500 to 100,000 K (blue LED pumping) and from 4900 to 50,000 K (n-UV LED pumping) without mixing with other phosphors. The blue LED-pumped WLED showed excellent white light (luminous efficiency=31.7 lm/W, Tc=6857 K) at 20 mA. This WLED showed a stable color coordinates property against an increase of the forward current. An n-UV LED-pumped WLED also showed bright white light (25.0 lm/W, 5784 K) at 20 mA.     

Tailored photoluminescence of YAG:Ce phosphor through various methods

Trivalent cerium Ce³⁺ (Ce) activated yttrium aluminum garnet Y₃Al₅O₁₂ (YAG) phosphor was synthesized by two methods: solid state reaction (SS), and combustion (CB) with urea, respectively. The crystallization and luminescent properties of the phosphors were studied. Factors influencing on the intensity of luminescence and the location of emission band of YAG:Ce, such as the type of flux used in SS, the reaction atmosphere, the concentration of activator, were investigated in detail. We accomplished red or blue shift of Ce emission band by a number of techniques in order to match with the variable emission wavelength of blue light emitting diodes. The change of emission in color coordinates was illustrated by chromaticity. Co-doping other rare earth ions with Ce³⁺ ions into YAG was attempted to increase the color rendering index.     

All-in-one-type organic light-emitting diodes for color tuning using phosphor in glasses with Pb-free silicate powders

We demonstrate all-in-one-type organic light-emitting diodes (OLEDs) that are fabricated using a color converting plate as a substrate. The color converting plate is Pb-free phosphor-in-glass (PiG), which is prepared by mixing Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) and SiO₂–B₂O₃–RO (R = Ba, Zn) glass frit by sintering at 750 °C for 30 min. The maximum luminance, luminance efficiency, and power efficiency of blue OLEDs fabricated on commercial glass are measured as 10500 cd/m², 10.18 cd/A, and 2.95 lm/W, respectively. The Commission Internationale de l'Eclairge (CIE) coordinates of blue OLEDs is (0.167, 0.325). Our obtained results show that the luminance value decreased as the PiG thickness increased, and the glass to phosphor (GTP) ratio decreased. The OLED devices fabricated on the PiG substrate (GTP ratio = 9:1, thickness: 150 μm) showed a maximum luminance, luminance efficiency, and power efficiency of 7600 cd/m², 8.76 cd/A, and 2.85 lm/W, respectively. The CIE color coordinates changed to (0.286, 0.504) at 200 mA/cm². These results proved that color coordination can be easily adjusted by varying the GTP ratio and the thickness of the PiG.     

White light emitting diodes (LEDs) with good color rendering indices (CRI) and high luminous efficiencies by the encapsulation of mixed and double-deck phosphors

In this paper, white light emitting diodes (LEDs) with good color rendering indices (CRI) and high luminous efficiencies have been fabricated by the encapsulation of mixed and double-deck phosphors. Experimental results revealed that white LEDs with the encapsulation of double-deck phosphors exhibited better CRI and higher luminous efficiencies than those with the encapsulation of mixed phosphors because no secondary excitation took place. The hue, CRI, and luminous efficiencies of white LEDs with double-deck phosphors under 200 mA were CIE_x,y = (0.357, 0.348), 90, and 62.3 lm/W, respectively while the hue, CRI, and luminous efficiencies of white LEDs with mixed phosphors under 200 mA were CIE_x,y = (0.366, 0.354), 89, and 56.5 lm/W, respectively.     

White LED based on nano-YAG:Ce3+/YAG:Ce3+,Gd3+ hybrid phosphors

Nano-YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺ phosphors were synthesized by glycothermal method. The X-ray diffraction (XRD) measurements showed that the samples can be well-crystallized at 600 °C. The transition electron microscope (TEM) showed that the particles have sizes mostly in the range between 35 and 100 nm. The YAG:Ce nano-phosphor had a wide emission band ranging from blue to yellow peaking at 532 nm, due to the transition from the lowest 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. Red-shift of emission peak wavelength from 532 nm to 568 nm has been achieved as doping Gd³⁺ ions into the YAG:Ce³⁺ to substitute some Y³⁺ ions. White LEDs were fabricated by combining GaN (460 nm) chip with the YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺. Color rendering index of the white LED as a function of the ratios of theses two kinds of phosphors was studied. As the ratio of YAG:Ce³⁺,Gd³⁺ phosphor increased, the color rendering index of the LED improved significantly under the forward bias of 20 mA. As the ratio of YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺ was 11:9, the white LED had a color rendering index, CIE chromaticity coordinates and color temperature T_c of 85, (0.3116, 0.3202) and 6564 K, respectively.     

Synthesis and optical properties of Ce-doped Y3Mg2AlSi2O12 phosphors

Y_3−xMg₂AlSi₂O₁₂:Ce_x³⁺ (x=0.015, 0.03 and 0.06) phosphors possessing garnet crystal structure were synthesized by the sol–gel combustion technique. The samples were characterized by application of powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, thermal quenching (TQ) and scanning electron microscopy (SEM). Moreover, luminous efficacies (LE), color points and quantum efficiencies (QE) were calculated. Optical properties were studied as a function of Ce³⁺ concentration and annealing temperature. XRD analysis revealed that sintering of polycrystalline Y₃Mg₂AlSi₂O₁₂:Ce³⁺ powders at 1550 °C results in nearly single-phase garnet materials. Phosphors showed broad emission band in the range of 500–750 nm and had the maximum intensity at 600 nm, which results in strongly red-shifted phosphors compared with conventional YAG:Ce phosphors emitting at 560 nm. However, strong concentration quenching has also been observed, probably due to increased Stokes shift.     

Enhancement of red spectral emission intensity of Y3Al5O12:Ce phosphor via Pr co-doping and Tb substitution for the application to white LEDs

We have enhanced color-rendering property of a blue light emitting diode (LED) pumped white LED with yellow emitting Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) phosphor using addition of Pr and Tb as a co-activator and host lattice element, respectively. Pr³⁺ addition to YAG:Ce phosphor resulted in sharp emission peak at about 610 nm through ¹D₂→³H₄ transition. And when Tb³⁺ substituted Y³⁺ sites, Ce³⁺ emission band shifted to a longer wavelength due to larger crystal field splitting. Y₃Al₅O₁₂:Ce³⁺, Pr³⁺ and (Y_1−xTb_x)₃Al₅O₁₂:Ce³⁺ phosphors were coated on blue LEDs to fabricate white LEDs, respectively, and their color-rendering indices (CRIs, R_a) were measured. As a consequence of the addition of Pr³⁺ or Tb³⁺, CRI of the white LEDs improved to be R_a=83 and 80, respectively. Especially, blue LED pumped (Y_0.2Tb_0.8)₃Al₅O₁₂:Ce³⁺ white LED showed both strong luminescence and high color-rendering property.     

UV excitable Y2? x ? y Gd y SiO5:Ce x phosphors for cool white light emission

Cool white light was realized in Y_2−x−y Gd _x SiO₅: Ce _y phosphor under near UV excitation, due to the occupation Ce³⁺ in Y³⁺ 1st and 2nd site, synthesized using solid state carbothermal reduction route. SEM with elemental analysis show the existence of Gd in Y₂SiO₅:Ce enhances the particles size in comparison to Y₂SiO₅:Ce phosphors alone. Gd³⁺ (0.00≤x≤0.75) and Ce³⁺ (0.02≤y≤0.10) concentration was optimized to 0.50 and 0.08 in Y₂SiO₅, respectively. The CIE chromaticity color coordinates (0.24, 0.20) are close to cool white light value which could be useful for the fabrication of cool white LED.     

白光LED极限流明效率的计算

对蓝光芯片加黄色荧光粉制备白光LED方法的流明效率进行了理论计算。根据光度学原理,我们考虑到视觉函数V(λ)的修正,以色坐标为x=0.325,y=0.332,显色指数为81.5,色温为5 914 K的白光LED发光光谱为依据,计算了白光LED流明效率的理论极限:得出每瓦白光LED辐射光功率产生的光通量为298.7 lm,白光LED发射的总光子数为2.7×10¹⁸。在理想情况下,注入一个电子-孔穴对产生一个蓝光光子,设荧光粉的量子效率为1,因此,注入的电子-孔穴对数亦等于白光光子数,进而计算出白光LED每辐射1 W的光功率所需的电功率为1.51 W,上述白光LED发光光谱对应的白光LED的电-光转换的理论极限流明效率为197.8 lm/W。     

Time-resolved luminescent spectroscopy of YAG:Ce single crystal and single crystalline films

The peculiarities of the luminescence and energy transfer from YAG host to the emission centers formed by the Y_Al antisite defects and Ce³⁺ ions have been studied in YAG:Ce single crystals, grown from the melt by modified Bridgman method in Ar and CO₂ + H₂ atmospheres, and YAG:Ce single crystalline film, grown by liquid phase epitaxy method, using the comparative time-resolved luminescent spectroscopy under excitation by synchrotron radiation in the range of fundamental adsorption of this garnet.     

Structural and magnetic properties of hydrides R3Fe29−xVxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and intrinsic magnetic properties of the hydrides R₃Fe_29−xV_xH_y (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed in this work. The lattice constants , and c and the unit cell volume of R₃Fe_29−xV_xH_y decrease with increasing rare-earth atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in regular anisotropic expansions along the a-, b-, and c-axes in this series of hydrides. Abnormal crystallographic and magnetic properties of Ce₃Fe_27.5V_1.5H_6.5, like Ce₃Fe_27.5V_1.5, suggest that the Ce ion is non-triply ionized. Hydrogenation leads to the increase in both Curie temperature for all the compounds and in the saturation magnetization at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Sm, Gd, and Dy, except for Tb. Hydrogenation also leads to a decrease in the anisotropy field at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Gd, Tb, and Dy, except for Sm. The Ce₃Fe_27.5V_1.5 and Gd₃Fe_28.4V_0.6 show the larger storage of hydrogen with y=6.5 and 6.9 in these hydrides.     

Ce3+-doped crystalline garnet films – scintillation characterization using α-particle excitation

Scintillating properties of Ce³⁺-doped (Lu,Y) aluminum garnet single crystalline films (SCF) were investigated. Thin SCF films of thickness between 1 and 30 μm were grown by a liquid phase epitaxy (LPE) method in various fluxes. The α-particle excitation (mainly 5.4857 MeV line of ²⁴¹Am) of pulse height spectra is used to measure scintillation response of SCF, especially peak of those α-rays which are totally absorbed in the films. Detailed studies and evaluation of scintillation measurements of large sets of Ce³⁺-doped SCF (Lu,Y) aluminum garnets showed that at present time (i) YAG:Ce SCF have comparable scintillation properties as YAG:Ce single crystals, especially their N_phels photoelectron yields are the same while (ii) scintillation properties of LuAG:Ce SCF do not reach those of LuAG:Ce single crystal.     

Effect of excitation level on the photoluminescence of barium thiogallate activated with europium and cerium ions

The photoluminescence of barium thiogallates doped with Eu²⁺, Ce³⁺, and Eu²⁺ + Ce³⁺ ions is studied over a wide range of excitation levels (10^–3–10⁶ W/cm²). Introduction of 3 at.% Eu and 3 at.% Ce instead of 5 at.% Eu into a BaGa₂S₄ matrix doubles the luminescence quantum yield of the phosphor. Doped BaGa₂S₄ exhibits a high linearity in its luminescence intensity as a function of excitation level (a constant efficiency) up to 2·10⁴ W/cm² for excitation pulse durations of 8 ns, which corresponds to cw pumping at a power density of about 5·10² W/cm² in terms of the concentration of excited ions. It is shown that using BaGa₂S₄:Eu,Ce along with the “yellow” phosphor of a Nichia NS6L083 LED may increase its color rendering index from 0.64 to 0.80 with no reduction in its luminous efficiency.     

Luminescence properties of Y3Al5O12:Ce nanoceramics

Comparative analysis of the luminescent properties of Y₃Al₅O₁₂:Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where Y_Al antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of Y_Al antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200-470 nm range related to Y_Al antisite defects and charged oxygen vacancies (F⁺ and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce³⁺ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce³⁺ ions.     

120 W high repetition rate Nd:YVO<Subscript>4</Subscript> MOPA laser with a Nd:YAG cavity-dumped seed laser

A master oscillator power amplifier (MOPA) system in which the output from an end-pumped Nd:YAG oscillator cavity dumped at 500 kHz is scaled up by a four-stage Nd:YVO₄ amplifier is reported. Decrease in extraction efficiency of the amplifier chain with crystals different from that in the oscillator was analyzed. With the 5.4 W seed output, 118 W of power was extracted from the amplifier chain at the pump power of 345 W, with an extraction efficiency of 34.2% and an overall optical–optical efficiency of 30.9% for the MOPA system. The beam quality factors were measured as M _x ²=1.45 and M _y ²=1.59 in two orthogonal directions, respectively.     

硼酸对亚微米级Ca3Sc2Si3O12:Ce绿色荧光粉的制备及发光性能的影响

采用凝胶-燃烧法合成了Ca₃Sc₂Si₃O₁₂ ∶Ce绿色LED用荧光粉,用X射线粉末衍射(XRD)、扫描电镜(SEM)、荧光光谱仪等对合成产物进行了分析和表征.结果表明:通过添加H₃BO₃做助熔剂,制得的荧光粉晶相纯正,颗粒形貌均呈现为较规则的类球形,而且所得荧光粉的粒径均小于1 μm.发射光谱呈现为一宽带,发射主峰位于505 nm,该宽峰对应于Ce³⁺关键词： 白光LED 荧光粉 3Sc₂Si₃O₁₂ ∶Ce')" href="#">Ca₃Sc₂Si₃O₁₂ ∶Ce 发光     

Peculiarities of luminescent properties of cerium doped YAG transparent nanoceramics

Optical and luminescence properties of transparent nanosized cerium doped Y₃Al₅O₁₂ (YAG:Ce) ceramics have been studied. YAG:Ce nanoceramics were obtained by means of low temperature and high pressure (LTHP) sintering method. Nanoceramic samples were sintered in the 2–8 GPa pressure range, whereas Ce³⁺ concentration was varied in the 0.5–5 at. % range. It is shown that, in contrast to the single crystal, a strong rise of absorption coefficient was detected already at wavelength shorter than 400 nm in all nanoceramic samples studied. Furthermore, in nanoceramic samples unusual UV emission band near 3.1 eV was observed, which is not observed in the YAG:Ce single crystal. High pressure applied during nanoceramics sintering leads to significant changes in their optical and luminescence properties.