Rapid microwave preparation of highly efficient Ce ³⁺-substituted garnet phosphors for solid state white lighting

Ce ³⁺-substituted aluminum garnet compounds of yttrium (Y ₃Al ₅O ₁₂) and lutetium (Lu ₃Al ₅O ₁₂)-both important compounds in the generation of (In,Ga)N-based solid state white lighting-have been prepared using a simple microwave heating technique involving the use of a microwave susceptor to provide the initial heat source. Carbon used as the susceptor additionally creates a reducing atmosphere around the sample that helps stabilize the desired luminescent compound. High quality, phase-pure materials are prepared within a fraction of the time and using a fraction of the energy required in a conventional ceramic preparation; the microwave technique allows for a reduction of about 95% in preparation time, making it possible to obtain phase pure, Ce ³⁺-substituted garnet compounds in under 20 min of reaction time. It is estimated that the overall reduction in energy compared with ceramic routes as practised in the lab is close to 99%. Conventionally prepared material is compared with material prepared using microwave heating in terms of structure, morphology, and optical properties, including quantum yield and thermal quenching of luminescence. Finally, the microwave-prepared compounds have been incorporated into light-emitting diode "caps" to test their performance characteristics in a real device, in terms of their photon efficiency and color coordinates.