Growth Of YAG:Ce³⁺-Al₂O₃ Eutectic Ceramics By HDS Method And Its Application For White LEDs

White LED（WLED） is called the fourth generation illuminant with high luminous efficiency, long life and energy-saving and environmental protection advantages, and it has gradually become the mainstream product in the lighting industry. Currently, WLED is made of blue LED chip coated YAG:Ce³⁺ yellow phosphor mainly. It has good performance, low cost and it is suitable for large-scale industrial production. However, packaging WLED need coat the resin which has poor thermal conductivity, so that the WLED device temperature will go up, and let WLED age gradually. Those will reduce the WLED’s photoelectric conversion efficiency and lead to a series of problems. My research is made YAG:Ce³⁺-Al₂O₃ eutectic ceramics by HDS method and use it as a new type of fl uorescent material used in WLED, in order to improve the thermal aging.The commonly used method included Czochralski（Cz） method, Vertical Bridgman（VB） method and Horizontal directional solidification（HDS） method for preparing the eutectic. Compared to the previous, HDS method is capable for producing large-size plate-like eutectic ceramics. My research was conducted on the basis of previous who with me in the same study group. Eventually, we have grown the YAG:Ce³⁺-Al₂O₃ eutectic ceramic which size is 170mm×90mm×20mm by HDS method successfully, and we conducted a series of b tests for the YAG:Ce³⁺-Al₂O₃ eutectic ceramic. In the analysis of XRD and SEM-EDS we can learn, the YAG:Ce³⁺-Al₂O₃ eutectic ceramic indeed is composed of Al₂O₃ phase and YAG:Ce³⁺ phase. The two phases interspersed with each other and let the whole eutectic ceramics form a three-dimensional network architecture. By the excitation spectra, emission spectra and XPS analysis we can kwon that Ce ions have fully translated into the Ce3+ in the YAG:Ce³⁺-Al₂O₃ eutectic ceramics. There are two peaks in the eutectic ceramics’ excitation spectra respectively at 345 nm and 475 nm, so it can be excited by the 470 nm blue LED chip. The eutectic ceramics’ emission range was between 485 nm to 675 nm, and the center wavelength is 555 nm, so it can emit yellow light. And we found that an air atmosphere annealing can eliminate the eutectic ceramics’ internal stress and oxygen vacancies to improve the quality of the eutectic ceramics. The YAG:Ce³⁺-Al₂O₃ eutectic ceramics’ Vickers hardness is about 16.75 GPa. Because of its great hardness, so as let its mechanical behavior become well.The processed eutectic ceramic pieces are used to test the quantum yield and temperature characteristic. In quantum yield tests, we can found that the best Ce doping ratio is about 0.25% from the eutectic ceramic which we have prepared, and for different Ce/Y eutectic ceramic pieces thickness changes affect their quantum yield is not obvious. For Ce/Y=0.25% of eutectic ceramic pieces after annealing, its quantum yield was greatly improve. And we found that reducing the pulling rate in favor of Ce3+ in the Ce/Y=0.5% of the eutectic ceramic pieces more evenly distributed, so that the quantum yield is improved. In temperature characteristic tests, we found that the eutectic ceramic pieces emission spectrum peaks are relatively stable in the case of temperature changes, so it has better temperature stability. The eutectic ceramic pieces package into WLED devices for light color electrical parameters of the test. Light color electrical test parameters include luminous flux and luminous efficiency, color rendering index, chromaticity coordinates and color temperature,standard deviation of color matching. By comparing the electrical parameters of the white LED light color in different conditions, and ultimately we can determine: the most suitable Ce/Y doping ratio was 0.25% in the present study;air atmosphere annealing can significantly improve the YAG:Ce³⁺-Al₂O₃ eutectic ceramic’s light color electrical test parameters; eutectic ceramic pieces thickness reduction can improve this white LED’s color rendering index, and let it’s color coordinate and color temperature closer to the pure white; Therefore, in the case of lower production costs as much as possible, this YAG:Ce³⁺-Al₂O₃ eutectic ceramics grown by these parameters which are Ce/Y = 0.25%, a thickness of 0.4mm, the pull rate of 20mm/h and annealing is more suitable for the production of white LED devices.