Influences of thermal post-treatment on the Mn valence states and luminescence properties of red-emitting Lu3Al5O12: Mn4+ transparent ceramic phosphors

Abstract The Lu3Al5O12: Mn4+ (LuAG: Mn4+) ceramic phosphors were prepared by solid-state reaction method under vacuum. The influences of the thermal post-treatment processes including treating atmosphere, temperature and holding time on the Mn valence state evolutions and luminescence properties of the LuAG: Mn4+ ceramics were elaborately studied. In-line transmittance and electron spin resonance (ESR) spectra were conducted to record the valence state evolutions of Mn ions. The PL spectra were measured to exhibit the influence of valence state of Mn on the luminescence properties. The results indicated that the thermal post-treatment is of great importance in preparing red-emitting LuAG: Mn4+. Specifically, the strong O2 oxidizing atmosphere is more favorable for converting Mn2+ into Mn4+. Mn2+ starts to be markedly oxidized to Mn4+ under 1400 °C heat-treatment in O2, and it can be totally oxidized into Mn4+ at 1600 °C. However, the most intense red emission occurs at 1500 °C. Further elongating the holding time at 1500 °C is an effective way to increase Mn4+ content, as well as the emission intensity of the ceramic phosphor.