Ce³⁺ Doped Al₂O₃-YAG Eutectic as an Efficient Light Converter for White LEDs

Ce³⁺ doped Al₂O₃-YAG eutectics were successfully grown by the horizontal directional crystallization method. The crystallization rate of eutectic growth was changed in the 1-7.5 mm/h range at a growth temperature of 1835 ℃. The microstructure of eutectic samples was investigated using scanning electron microscopy and X-ray microtomography. The intrinsic morphology of eutectic represents the stripe-like channel structure with a random distribution of the garnet Y₃Al₅O₁₂ (YAG) and Al₂O₃ (sapphire) phases. The content of these phases in the stripes changes in the 52.9-55.3% and 46.1-47.1% ratios, respectively, depending on the growth rate of the crystallization of the eutectic samples. The luminescent properties of the eutectic demonstrated the dominant Ce³⁺ luminescence in the garnet phase. The luminescence of the Ce³⁺ ions in Al₂O₃ has also been observed and the effective energy transfer processes between Ce³⁺ ions in the Al₂O₃ and YAG garnet phases were revealed under high-energy excitation and excitation in the UV Ce³⁺ absorption bands of sapphire. The phosphor conversion properties and the color characteristics (Al₂O₃-YAG):Ce eutectic with different thicknesses were investigated under excitation by a blue LED. We have also tested the prototypes of white LEDs, prepared using a blue 450 nm LED chip and (Al₂O₃-YAG):Ce eutectic photoconverters with 0.15 to 1 mm thicknesses. The results of the tests are promising and can be used for the creation of photoconverters for high-power white LEDs.