Red-emitting Lu3Al5O12: Mn transparent ceramic phosphors: valence state evolution studies of Mn ions

A red-emitting Lu3Al5O12: Mn (LuAG: Mn) transparent ceramic phosphor was successfully prepared via a two-step process: vacuum sintering and further high-temperature annealing in air. The LuAG: Mn ceramics with a transmittance of similar to 40% in visible light were obtained after vacuum sintering. Through the transmittance spectra, electron spin resonance measurement, cathodoluminescence technology and photoluminescence spectra, valence state evolution of Mn ions in LuAG ceramics before and after annealing were elaborately demonstrated. It's proved that part of Mn2+ were oxidized to Mn4+ during the annealing process, which is responsible for the bright red emission of the annealed sample under ultraviolet light excitation. The red-emitting LuAG: Mn transparent ceramic phosphor is a promising candidate to help make white light-emitting diodes (WLEDs) with high color rendering index.