Microstructures, optical properties and application in WLEDs of large-size YAG:Ce3+-Al2O3 eutectic grown by HDS method

Large-size YAG:Ce (3+)-Al2O3 eutectics with the dimensions of 170 mm x 160 mm x 25 mm, a resin-free phosphor for WLEDs, were successfully grown by HDS method. The influence of annealing, growth rate, the mole ratio of Ce/Y on microstructures and optical properties of the eutectics and the preferred orientations in different cross-sections of the eutectics were investigated. Increasing the growth rate and annealing in the air atmosphere could appropriately increase the intensity of excitation and emission spectra of the eutectics. The coarse microstructure regions in the eutectics were triggered by the doping of Ce, meanwhile unconnected layer-type and connected network-type coarse microstructure appeared on the parallel cross-section (perpendicular to X) and the perpendicular cross-section (perpendicular to Z), respectively. Ce-rich phase was formed in the microstructures of the eutectics when Ce/Y exceeded 0.50%. At the same time, the valence of Ce in Ce-rich phase was determined by XPS and EDS. The influence of the eutectic pieces' transmittance on the luminous characteristics of the WLEDs with those pieces was analyzed. The results showed that WLED with the fine polished eutectic piece was performed much better than the traditional WLEDs. (C) 2018 Elsevier B.V. All rights reserved.