Influence of Ce ion Concentration on Fluorescence Properties of Ce: TAG-Al2O3 Eutectic Mixed Crystals

Combining a blue LED chip with phosphor, white light can be obtained. In traditional white LEDs, the phosphor was dispersed in resin in a form of particles. Particle-resin composite has complex packaging and poor thermal stability. For high-power white LEDs, this combination cannot provide long-term stable work because of photo-degradation of the organic epoxy resin under high irradiation and high temperatures. Here we develop resin-free phosphor (Tb(1-n)Cen)(3)Al5O12-Al2O3 eutectic mixed crystals (Ce: TAG-Al2O3) to eliminate the photo-degradation issue of the organic material. They were grown by optical floating zone method. X-ray diffraction and scanning electron microscopy show that these materials have typical eutectic mixed crystal structure of sapphire and garnet phases, in which lamellar spacing is in an order of tens of microns. The doped Ce3+ ions do not influence basic structure of TAG crystal. Ce3+ ion replaces Tb3+ ion rather than Al3+ ion. Photoluminescence emission and excitation properties of the eutectic mixed crystals were investigated. They get to maximal value with 2.0% Ce-3+,Ce- and have wide excitation band at 470 nm. Luminous efficiency of eutectic mixed crystal- packaged LED is higher than that of particle- resin composite packaged LED. These results show that Ce: TAG-Al2O3 eutectic mixed crystals are promising phosphor for white LEDs.