YAG Phosphor Research Articles

Temperature Dependent Energy Transfer in Ce3+-Yb3+ Co-Doped YAG Phosphors

Ce3+-Yb3+ co-doped Y3Al5O12 (YAG) phosphors were prepared, and their photoluminescence spectra, photoluminescence excitation spectra and fluorescence decay curves were measured at different temperatures from 8 K to 300 K. Experimental results show that, besides thermal quenching effect, the energy transfer is also the mechanism for the temperature dependence of the Yb3+ emission. A photo-induced Ce-O-Yb charge transfer state model is proposed to explain the variation of the emission with the temperature. The decay curves of the co-doped YAG phosphors at different temperatures can also be explained by the model.

Rare-earth-free red-emitting K2Ge4O9:Mn(4+) phosphor excited by blue light for warm white LEDs.

A series of novel K2Ge4O9:Mn(4+) phosphors with red emission under blue light excitation have been synthesized successfully by traditional high-temperature solid-state reaction. The structure of K2Ge4O9 has been investigated by high-resolution transmission electron microscopy, scanning electron microscopy and X-ray powder diffraction with Rietveld refinement. The PL properties have been investigated by measuring diffuse reflection spectra, emission spectra, excitation spectra, decay curves and temperature-dependent spectra. The KGO:0.1% Mn(4+) phosphor can emit red light peaking at 663 nm under UV or blue light excitation. The critical quenching concentration of Mn(4+) was about 0.1 mol%. The concentration quenching mechanism could be a d-d interaction for the Mn(4+) center. The CIE chromaticity coordinates and FWHM are (0.702, 0.296) and 20 nm, which demonstrated that the K2Ge4O9:Mn(4+) has a high color purity. By tuning the weight ratio of yellow and red phosphors, the fabricated white LEDs, using a 455 nm InGaN blue chip combined with a blend of the yellow phosphor YAG:Ce(3+) and the red-emitting KGO:Mn(4+) phosphor driven by a 40 mA current, can get white light with chromaticity coordinates (0.405, 0.356) and CCT 3119 K. These results indicated that K2Ge4O9:Mn(4+) is a potential red phosphor to match blue LED chips to get warm white light.

Optical and reliability properties studies of green YAG phosphors by Ga substitution

In this paper, green Y2.94(Al1−xGax)5O12:0.06Ce phosphors were prepared by conventional solid-state reaction. The crystal structures, the influence of Ga concentration on the photoluminescence, thermal stability and reliability properties of the phosphors were studied. The PL emission bands of Y2.94(Al1−xGax)5O12:0.06Ce showed blue shift from 545 nm to 525 nm with increasing Ga content (x value) under excited at 460 nm. The thermal stability of Y2.94(Al1−xGax)5O12:0.06Ce phosphor is hindered by adding Ga. As the temperature increases from 300 to 500 K, the PL intensity of Y2.94(Al0.8Ga0.2)5O12:0.06Ce and Y2.94(Al0.65Ga0.35)5O12: 0.06Ce phosphor decreases by 11.11 and 16.57 %, respectively. Reliability test results show that the relative PL intensity of Y2.94(Al1−xGax)5O12:0.06Ce phosphor decrease to from 99.76 to 95.37 % with x value increased from 0.15 to 0.35 after the ambient condition of 85 °C/RH 85 % for the exposure time of 168 h. And the relative PL intensity of Y2.94(Al1−xGax)5O12:0.06Ce phosphor decrease to from 99.53 to 91.78 % after soaking into boiled water for 4 h. It can be summarized that the addition of Ga deteriorates the thermal stability as well as the reliability of the phosphors slightly.

A flux-free method for synthesis of Ce3+-doped YAG phosphor for white LEDs

A series of CeF3-doped Y3Al5O12 (YAG:CeF3) phosphor, CeO2-doped Y3Al5O12 (YAG:Ce2O3) phosphor and 5wt% BaF2 added YAG:Ce2O3 (YAG:Ce2O3+BaF2) phosphor were successfully synthesized by a solid-state reaction method. The microstructure, morphology, luminescence spectra, luminescence quantum yield (QY) and thermal quenching of the phosphors were investigated. The QY of YAG:CeF3 phosphor is 91% but the QY of YAG:Ce2O3 phosphor is just 80%. At 150°C, the luminescence intensity of YAG:CeF3 phosphor, YAG:Ce2O3 phosphor and YAG:Ce2O3+BaF2 phosphor was 85%, 86% and 89% of that measured at 25°C, respectively. The comprehensive performance of the white LED lamp employing YAG:CeF3 phosphor is even better than that of the white LED lamp employing YAG:Ce2O3+BaF2 phosphor. The experimental results show that it is a promising flux-free method to synthesize Ce3+-doped YAG phosphor by employing CeF3 as the Ce3+ source.

Layered Ceramic Phosphors Based on CaAlSiN3:Eu and YAG:Ce for White Light‐Emitting Diodes

To develop warm‐white light‐emitting diodes via conversion phosphors, blue light‐emitting diodes are generally combined with mixtures of green and red‐emitting phosphor powders. Generally, the phosphors are provided by resin embedded particle dispersions. Such resin‐based solutions cause several drawbacks with respect to LED lifetime and quality. Therefore, it has been investigated whether the red‐emitting nitride phosphor CaAlSiN3:Eu and the green‐emitting oxidic phosphor YAG:Ce can be cofired to layered ceramic composites. The shrinkage behavior and the composition of the interface in dependence of sintering temperature and the effect of interdiffusion processes at the interface on the luminescence properties were investigated. The formation of secondary phases at the interface in the cofired structures was found to limit the phosphor functionality for the nitride‐based CaAlSiN3:Eu in such composite ceramics. To counteract this, sacrificial interlayers were introduced to produce multilayered ceramics comprising CaAlSiN3:Eu and YAG:Ce for LED lighting applications. It is shown for the first time, that it is possible to sinter layered CaAlSiN3:Eu and YAG:Ce composite ceramics in a pressureless process at moderate sintering temperatures if one uses thin‐film passivated interfaces to reduce luminescence‐disturbing diffusion phenomena. These results demonstrate that diffusion barriers can be suitable means to obtain layered ceramic composites comprising CaAlSiN3:Eu and YAG:Ce in a pressureless sintering process with good optical properties.

Comparison and analysis of Eu3+ luminescence in Y3Al5O12 and Y3Ga5O12 hosts material for red lighting phosphor

This paper reports on the comparative investigation of the spectroscopic properties of the Y3Al5O12 (YAG) and Y3Ga5O12 (YGG) doped with Eu3+ synthesized by the combustion method. A pure phase was identified for the YGG phosphor, but one other phase was observed for the as-prepared and annealed YAG phosphor. A high intense red color emission was observed from Eu3+ doped YAG compared to the orange-red color of Eu3+ in the YGG phosphor. The optimum Eu3+ concentration was found to be higher in the YGG compared to the optimum Eu3+ concentration in the YAG. A spectroscopic investigation on the concentration quenching effect and the covalency of the Eu–O bond were carried out on the basis of the substitution of Ga3+ and Al3+in the garnet host. Judd–Ofelt parameters, different spectral and colorimetric parameters were estimated theoretically from the experimental curves, for both the hosts to determine the better luminescence media.

A novel high color purity yellow luminescent material NaBaBO3:Sm3+

Yellow emitting Sm 3+-doped NaBa 1-x BO 3(0.01 ≤ x ≤ 0.13) phosphors were synthesized by conventional solid state reaction method. The phase structure and luminescence properties of the as-prepared phosphors were investigated. These phosphors can be effectively excited by 403 nm near-ultraviolet light and feature a satisfactory yellow performance. The emission peaks are observed at 560 nm, 603 nm and 650 nm, originating from the transitions of 4G5∕2→6H5∕2, 4G5∕2→6H7∕2 and 4G5∕2→6H9∕2 respectively. Investigation of Sm 3+ concentration-dependent emission spectra indicates that the NaBa 0.95 BO 3:0.05 Sm 3+ phosphor shows the strongest yellow emission intensity and exhibits the CIE value of x = 0.4760 and y = 0.5090. Through the theoretical calculation, a high color purity of 96.0% was determined for the NaBaBO 3: Sm 3+ phosphor, and the color purity of NaBaBO 3: Sm 3+ is much higher than that of the commercial yellow phosphor YAG : Ce 3+. This work is highly relevant to the development of a new type of potential down-conversion (DC) yellow phosphor for near ultraviolet white or yellow light-emitting diodes (LEDs).

Modeling of reflection-type laser-driven white lighting considering phosphor particles and surface topography.

This paper presents a model of blue laser diode (LD)-based white lighting coupled with a yellow YAG phosphor, for use in the proper design and fabrication of phosphor in automotive headlamps. First, the sample consisted of an LD, collecting lens, and phosphor was prepared that matches the model. The light distribution of the LD and the phosphor were modeled to investigate an effect of the surface topography and phosphor particle properties on the laser-driven white lighting systems by using the commercially available optical design software. Based on the proposed model, the integral spectrum distribution and the color coordinates were discussed.

Betavoltaic Cells Using P3HT Semiconductive Conjugated Polymer

The need for extreme-duration light-weight power sources for space applications motivates the study and development of polymer-based betavoltaics. The betavoltaic device, based on the semiconductive polymer-fullerene blend of poly(3-hexylthiophene): indene-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> bisadduct (P3HT:ICBA), is demonstrated here for the first time. Both direct and indirect energy conversion methods were explored. For the indirect conversion method, a phosphor intermediate layer of cerium-doped yttrium aluminum garnet (Ce:YAG) was used on top of the polymer device. A high open circuit voltage of 0.56 V has been achieved in the betavoltaic device fabricated on a polyethylene terephthalate (PET) substrate with indirect energy conversion at 30-keV electron kinetic energy. The maximum output electrical power of 62 nW was achieved at 30-keV input electron beam (e-beam) energy. The highest betavoltaic power conversion efficiency of 0.78% was achieved at an e-beam energy of 10 keV. Using the thin PET substrate instead of a glass substrate for the polymer device and phosphor screen fabrication, the betavoltaic device performance has been significantly improved due to a reduction in physical distance between photon-generating Ce:YAG phosphor screen and photon-absorbing P3HT:ICBA layer. The use of the PET substrates helped by significantly decreasing the directional and external interaction losses.

Effect of glass composition on the luminescence characteristics of color conversion glasses in BaO–ZnO–B2O3–SiO2 glasses

The effect of glass composition on the properties of color conversion glasses was examined for five BaO–ZnO–B2O3–SiO2 glasses, comprised of different mol% of each of the four components. The five color conversion glasses were prepared by sintering a mixture of glass frits and a YAG phosphor. The content of the YAG phosphor was maintained at 5wt.%. The characteristics of color conversion glasses, with respect to luminous efficacy, luminance, CIE (Commission International de I'Eclairage) chromaticity, CCT (Correlated Color Temperature) and CRI (Color Rendering Index) were analyzed based on luminescence emission spectra. These characteristics were dependent on the ratio of each component in the BaO–ZnO–B2O3–SiO2 glasses. KPG-102, containing 40mol% BaO, showed best luminous efficacy even though the sintering temperature of LED-102 matrix glass was not lowest. As the refractive index of matrix glasses was increased, luminous efficacy was also increased. But in case of color conversion glass, containing 40mol% ZnO, showed the lowest value for the chemical interaction between the phosphor and glass matrix even though the refractive index of its matrix glass was the highest.

The Investigations of the Pr, Gd, Si–N Doping, and Phosphor Curvature Effects on the Performances of YAG‐Based WLEDs

The effect of the phosphor curvature in the range 0.1766–0.2589 mm−1 on the luminous efficacy of Y2.95Al5O12:0.05Ce3+ (YAG)‐based white‐light‐emitting diodes (WLEDs) was investigated at the similar correlated color temperature (CCT) of ~6300 K by tuning the concentration of YAG phosphors in the phosphor layer ranging from 7.5 to 15 wt%. It was found that both the luminous efficacy and luminous power increased monotonically with the increasing curvature. The luminous efficacy (=82.4 lm/W) and luminous power (=297.85 mW) of the YAG‐based WLED at the preferable phosphor curvature of 0.2589 mm−1 were 19.44% and 17.36%, respectively, higher than those at the curvature of 0.1766 mm−1 under 350 mA. This finding reveals that the surface curvature of phosphor layers is a critical factor which cannot be ignored for the investigation of the light output of phosphor‐converted WLEDs. Moreover, the color rendering index (CRI) enhancement of YAG‐based WLED with substitution of Y2.94Al5O12:0.05Ce3+, 0.01Pr3+ (YPrAG), Y2.45Gd0.5Al5O12:0.05Ce3+ (YGdAG), and Y2.95Al4.8Si0.2O11.8N0.2:0.05Ce3+ (YAlSiON) for YAG were assessed under the same phosphor curvature of 0.2589 mm−1 and the similar CCT ~6350 K. Taking the luminous efficacy, preparation cost of phosphors, and CRI into consideration, we suggest that the YGdAG is a preferable candidate for replacing the YAG for use in WLEDs among the four kinds of phosphors. Compared with the YAG (7.5 wt%)‐based WLED, the YGdAG (7 wt%)‐based WLED exhibited an improved CRI, less preparation cost of phosphors, and the acceptable reduction in luminous efficacy under 350 mA.

Efficient near-infrared downconversion and energy transfer mechanism of ce(3+)/yb(3+) codoped calcium scandate phosphor.

An efficient near-infrared (NIR) downconversion has been demonstrated in CaSc2O4: Ce(3+)/Yb(3+) phosphor. Doping concentration optimized CaSc2O4: 1%Ce(3+)/5%Yb(3+) shows stronger NIR emission than doping concentration also optimized typical YAG: 1%Ce(3+)/5%Yb(3+) under 470 nm excitation. The NIR emission from 900 to 1100 nm is enhanced by a factor of 2.4. In addition, the main emission peak of Yb(3+) in the CaSc2O4 around 976 nm matches better with the optimal spectral response of the c-Si solar cell. The visible and NIR spectra and the decay curves of Ce(3+): 5d → 4f emission were used to demonstrate the energy transfer from Ce(3+) ions to Yb(3+) ions. The downconversion phenomenon has been observed under the direct excitation of Ce(3+) ions. On analyzing the dependence of energy transfer rate on Yb(3+) ion concentration, we reveal that the energy transfer (ET) from Ce(3+) ions to Yb(3+) ions in CaSc2O4 occurs mainly by the single-step ET process. Considering that the luminescence efficiency of CaSc2O4: Ce(3+) is comparable to that of commercial phosphor YAG: Ce(3+), the estimated maximum energy transfer efficiency reaches 58% in the CaSc2O4: 1%Ce(3+)/15%Yb(3+) sample, indicating that CaSc2O4: Ce(3+)/Yb(3+) sample has the potential in improving the conversion efficiency of c-Si solar cells.

An X-ray image intensifier for microsecond time-resolved experiments

Persistence of an X-ray image intensifier with a YAG (P46, Y3Al5O12:Ce3+) phosphor in the output window was examined using X-ray pulses from a storage ring and a high-speed CMOS camera. Because of the fast decay of the YAG fluorescence (60 ns), persistence of CsI:Na+ in the input window dominates the decay of intensity of the image intensifier. As reported before, persistence of CsI:Na+ had two major components when fitted with two exponential functions, a fast one around 600 ns and a slow one about 7 μs. In addition, it was found that a slower component, which is small but takes tens of microseconds to decay, also exists. Thus, this detector should be used with caution at a time resolution higher than about 50 μs when high accuracy of measurement is required.

基于CuInS2/ZnS核壳结构量子点的高光效暖白光LED

A stepwise hot-injection method was proposed to synthesize Cu In S2/ Zn S( CIS / Zn S)core / shell quantum dots. Based on CIS quantum dots,the emission bands of the prepared CIS / Zn S quantum dots can be tuned from 570 to 650 nm by varying Cu / In ratio. Compared to the low quantum yields of CIS quantum dots,the quantum yields of CIS / Zn S core / shell quantum dots can reach78%. The white LEDs with warm tone were successfully obtained via spin-coating CIS / Zn S quantum dots on the yellow phosphor YAG∶ Ce3 +. The experimental results indicate that the white LEDs possess high luminous efficiency of 244. 58 lm / W under 10 m A current density. As a result of joining CIS / Zn S quantum dots,the prepared white LEDs display higher color rendering index( CRI) of about 82. 7 and warm white light with a correlated CIE parameters of( 0. 340 6,0. 369 0).

Phosphor modeling and characterization

The prevalent method to develop a phosphor recipe (based on trial and error) to create white light with a blue light-emitting diode (LED) is time-consuming. We developed a new method for determining parametric values in a simulated phosphor model through systematic testing of phosphor samples and optimizing the parameter values with ray-trace software. The model employs Mie volume scattering together with absorption and down-conversion. A double-integrating sphere spectral measurement system was constructed to perform phosphor characterization. It was used to characterize a YAG phosphor over a wide range of phosphor concentrations and thicknesses. The final phosphor model was proven to accurately predict the phosphor performance.

Development in Phosphor Glass Ceramic Composites

The Bi doped borosilicate glass systems with low characteristic temperature and high refractive index were fabricated. Through microstructure control by Bi and Zn doping, a low softening point around 476oC of the glass was achieved. The YAG phosphor was successfully embedded and dispersed into the softened glass substrate under heat treatment. The emission light of GCP sample can be controlled from blue to white and yellow under LED blue chip package through heat treatment.

Thermal analysis of a nano-pore silicon-based substrate using a YAG phosphor supported COB packaged LED module

This paper presents the development of a nano-pore silicon-based (NPSB) substrate as a thermal substrate for multi-chip array light-emitting diodes (LEDs) using a YAG phosphor supported chip-on-board (COB) package structure. The proposed structure of the substrate has a nanoporous anodised aluminium oxide (AAO) layer and silicon dioxide (SiO2), that are deposited by electroplating plasma-enhanced chemical vapour deposition (PECVD) on a thermally oxidised silicon wafer, respectively. To analyse the thermal characteristics of the proposed substrate, we use an InGaN blue LED with a 5 W multi-chip array and an individual LED chip size of 900 μm × 900 μm × 150 μm. The thermal performance was investigated, the junction temperature was estimated using the computational fluid dynamic (CFD) solver package, and the measurement results were validated using an infrared (IR) camera and the thermal transient tester (T3ster). Due to the effect of the cerium-activated yttrium aluminum garnet (YAG:Ce3+) yellow phosphor package on an NPSB thermal substrate, the parallel heat flow generates and induces reduction of the overall thermal resistance by as much as 0.3 K/W.

High thermal stability phosphor: Red-emitting LiBaPO4:Sm3+

LiBa1−xPO4:xSm3+ phosphors with various concentrations of Sm3+ ions (x=0.01, 0.03, 0.05, 0.07 and 0.09) were successfully synthesized via microwave-assisted sintering at 900°C for 3h under an air atmosphere. The concentration quenching effect occurred when the concentration of Sm3+ ions is x=0.05. The thermal quenching temperature T50 was found to be 500°C, which is higher than that of the commercial YAG phosphor. The high activation energy ΔE of the LiBa0.95PO4:0.05Sm3+ phosphor was calculated to be 0.6eV. Increasing Sm3+ ions gradually decreased the lifetime of the Sm3+ ions from 3.13 to 2.95ms. All the chromaticity (x, y) of the prepared LiBa1−xPO4:xSm3+ phosphors are located in the red region (0.57, 0.41). Moreover, the electroluminescence intensities increase as the current increases from 350 to 600mA, indicating that LiBa0.95PO4:0.05Sm3+ phosphor prepared by microwave-assisted sintering exhibits excellent thermal stability, making it suitable for use as luminescent material for WLEDs.

Development in Phosphor Glass Ceramics Composites

Glass ceramics containing phosphor, GCP, has become an advanced material in high power LED lighting application recently due to its superior optical and thermal performance and elongated lifetime. Glass systems which have lower characteristic temperatures , glass transition temperature(Tg) and glass softening point(Td)…, as well as excellent mechanical strength and chemical stability, are proposed in microelectronics technology, infrared laser technology and sealing of materials. Borosilicate glass systems exhibit lower characteristic temperatures and quality optical properties. By controlling functional elements, further enhancement in thermal, mechanical, and optical properties can deduced. In this study, the YAG phosphor powders embed into designed glasses under controlled atmosphere to from glass ceramics phosphor composites. The thermal, optical properties and structure of borosilicate glass host are discussed. Heat treatment which affects the YAG phosphor incorporation into the glass is also considered. The glass transition temperatures(Tg) and softening points(Td) are 447~483oC, and 476~524oC respectively. A high refractive index of 1.85~1.94 can be reached. The results show that the developed borosilicate glass hosts are suitable for GCP matrix to contain phosphor powders. The YAG phosphor powders are well contained and dispersed in the glasses.Key words: LED, Glass ceramics phosphor composites(GCPC), Low characteristic temperature, Heat treatment

A study on luminescence properties and energy transfer mechanism for NaCaY(PO₄)₂:Eu²⁺,Mn²⁺ phosphors for LED applications.

A color-tunable NaCaY(PO₄)₂:Eu²⁺,Mn²⁺, was synthesized by a solid state reaction. NaCaY(PO₄)₂ crystallizes in the hexagonal structure system with space group of P6₂22 and Z = 1. The NaCaY(PO₄)₂:Eu²⁺ exhibits blue-greenish emission and broad excitation bands corresponding to the allowed f→d electronic transition of Eu²⁺. In addition, via the design of efficient energy transfer from Eu²⁺ to Mn²⁺, a high quality of white-emitting light could be generated in the optimized composition of NaCaY(PO₄)₂:1%Eu²⁺, 0.5%Mn²⁺ with CIE coordinates of (0.3389,0.3531) and CRI of 82, which is superior than that of blue chip and YAG phosphors. The results indicate that as-synthesized NaCaY(PO₄)₂:Eu²⁺,Mn²⁺ phosphors exhibits the potential to be an n-UV convertible phosphor.