Papers by Keyword: YAG

Abstract: 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.

Abstract: Green LL is observed in Ce doped Gd₃Al₅O₁₂: Ce, Ga garnet phosphors. LL is well correlated with Ce³⁺ emission and a peak around 150°C in the TL glow curve. In comparison with the commercial phosphor YAG, the Gd₃Al₅O₁₂: Ce, Ga (GAG) is more stable and shows more intense TL properties, this phosphor can be used for dosimetry detections and measurements. Gd₃Al₅O₁₂ activated with Ce (0.7 mol.%) phosphors were prepared by combustion synthesis. The long-lasting luminescence (LL) is also reported in Pr³⁺ and Ce³⁺ doped in reducing atmosphere in YAG phosphor. But YAG: Ce gives yellow emission which doesn’t suit LL applications. On the other hand, Ga substituted GdAG: Ce phosphor gives green emission at shorter wavelengths. In this paper we explored Ga substituted GdAG: Ce phosphor prepared by combustion synthesis for LL, results of these investigations are reported in this paper.

Abstract: In this paper, the YAG powder is prepared by the co-precipitation method. In addition, the sintering aid to aid sintering and the high temperature foaming agent that becomes gas released during the heating process so that the sample has pores, the ball mill mixes the material, and the sample press is extruded. Box-type resistance furnace sintering. Through this process, porous ceramics can be made. Study the effect of sintering aid content, foaming agent type, sintering temperature on the properties of YAG porous materials. The analysis and discussion can lead to the following conclusions: as the content of sintering aid silica in the sample increases, the sintering temperature of the sample decreases. It is best when the ratio of sintering aid alumina to silica is 3:1. The moldability of the sample whose foaming agent is wood chips is worse than that of the sample whose foaming agent is fiber and carbon powder. The ratio of sintering aid alumina to silica is 3:1, and the sintering temperature of the sample with carbon powder as the blowing agent is best when the sintering temperature is 1400 °C.

Abstract: Polycrystalline yttrium aluminium garnet (YAG) ceramic has been prepared using microwave sintering. Micron-sized of Al₂O₃ and Y₂O₃ powders were mixed through in house fabrication mixer for 24 hours before calcined at 1100 °C and palletization process. The effect of sintering parameters on the microstructures was observed at various and holding times. X-ray diffraction (XRD) analysis was carried out to determine and quantify phase transformation with respect to these parameters. It was found that three phases namely YAM (Y₄Al₂O₉), YAP (YAlO₃) and YAG have been identified. While both grain sizes and density of sintered samples were found increased from 1.4 μm to 2.46 μm and 90% to 98%, respectively. Therefore, microwave sintering has a significant effect on the densification behavior of YAG.

Abstract: YAG materials have a number of unique properties, the application is very extensive. In order to improving the properties of YAG porous materials, the effect of forming processing on the properties of YAG porous ceramics is investigated. Through the results and analysis, the conclusions showed that the porosity of YAG porous ceramics gradually decreased with the molding pressure increases, and the compressive strength of YAG porous ceramics shows a rising trend. The size and number of pores in the microstructure are reduced with increasing the forming pressure, there are inherently many voids in the YAG porous ceramics body at low forming pressures. The porosity of YAG porous ceramic decreases with the increase of dwell time, however, the process of extending from 5 min to 10 min is much faster than the rate of descending from 10 min to 15 min. The size and number of pores in the microstructure are reduced with extending the holding pressure time, which also makes YAG porous ceramics pose the higher mechanical strength. Through the analysis of the results, when the forming pressure is 10MPa, the porosity of YAG porous ceramics is 41.11% and the compressive strength is 5.8MPa, the porosity and compressive strength of YAG porous ceramics is better.

Abstract: In this paper transparent chromium and neodymium co-doped YAG ceramics were prepared by slip casting and vacuum sintering using high purity Al₂O₃, Y₂O₃, Nd₂O₃ and Cr₂O₃ powders. After mixing the high purity Al₂O₃, Y₂O₃, Nd₂O₃ and Cr₂O₃ powders under the appropriate percentages, pure phase Cr-Nd-doped YAG powders were preparated via calcining at 1300°C for 2 hours. The slurry with the solid content of 40% was casted by self-pressure slip casting under 25°C and 60% humidity to obtain green body. The green body was dried for 96 hours at 33 °C and 75% humidity and then sintered at 1800 °C for 10 hours in vacuum to obtain Cr,Nd:YAG ceramics finally. The transmittance of 1.0 at.%Cr,1.0 at.% Nd:YAG is nearly 80% at 1064nm, and two absorption peaks of Nd³⁺ can be seen near 760 nm and 808 nm.

Abstract: YAG materials have a number of unique properties, the application is very extensive, the burn is due to the temperature is too high or the residence time at high temperatures is caused. The undercurrent is the sintering temperature is too low or the holding time is not enough, resulting in product performance is too low or too small shrinkage. In this paper, the effect of sintering temperature on properties of YAG porous ceramics was investigated. The results showed that the firing temperature of the ingredients will be different and cause the same sintering process and sintering additives content of different samples burned. The increase in the content of SiO₂ in the furnish with the sintering aid tends to occur. the effect of temperature on the mechanical properties of the samples after sintering was significant, so the raw materials include 60wt%YAG, 10wt% CaO, 10wt% SiO₂ and 20wt% soluble starch, the molding process in 20MPa pressure 10min, the sintering at 1500°C for 2h, the sample porosity is 42.2%, the compressive strength is 5.8MPa, the outside shape is keep intact and the better pore microstructure is shown.

Abstract: YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by co-precipitation method and hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that the precursor powder prepared via the co-precipitation method is mainly from amorphous to crystalline transition with the increasing calcination temperature, the precursor agglomeration is more serious, In the process of increasing the calcination temperature, the dispersibility of the roasted powder is greatly improved, which is favorable for the growth of the crystal grains, so that the particle size of the powder is gradually increased, the YAG precursor prepared by the co-precipitation method is transformed into YAG crystals, the phase transition occurs mainly between 900 and 1100°C. When the molar ratio of salt to alkali is Y³⁺: OH^-=1: 8 via the hydrothermal reaction, the YAG particles with homogeneous morphology can be obtained. When the molar ratio of salt and alkali is increased continuously, the morphology of YAG particles is not obviously changed. The co-precipitation method is easy to control the particle size, the hydrothermal method is easy to control the particle morphology.

Abstract: YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that when the molar ratio of salt to alkali that Y³⁺: OH^- is 1:8, the more uniform morphology of the particles can be prepared, when the molar ratio of salt to alkali is increased, the morphology of the particles will not change. The reaction time is longer, the particle size will be thicker. The smaller the concentration of Y³⁺ ions is, the larger the particle size will be small. The experimental results show that the rod-like particles have a poly-crystal structure at the reaction temperature of 200°C, reaction time of 2 days and the molar ratio of salt to alkali of 1:8. The diameter of the rod-like particles is most of the powders have a particle size of 1000 nm and a small amount of powder has a particle size of about 5000 nm. The purity of powder is higher through the test of XRD.

Abstract: The shell structure YAG composite powders with different volume fraction (15, 20 and 25vol%) micro h-BN have been prepared by co-precipitation process. The bulk composites were performed by pressure sintering at 1600°C under a pressure of 30MPa in vacuum. The mechanical properties (elastic modulus, hardness, and fracture toughness) and relative density of the composites were investigated detailedly. Furthermore, phase composition and microstructure of the composites were analyzed thoroughly by X-ray diffraction, scanning electron microscopy. Meanwhile, good machinability is maintained due to the low hardness of the second phase.