Synthesis and characterization of Mn-activated lithium aluminate red phosphors

Mn-doped LiAlO2 powders were synthesized by the sol–gel method. The crystalline phase of the sol–gel-derived host lithium aluminate could be successfully controlled as α-LiAlO2 single phase by heat treatment at 700 °C. The results of electron spin resonance spectroscopic analyses revealed that Mn ions existed as isolated Mn4+ and clustered cations in the host α-LiAlO2 matrix, and a part of the isolated Mn4+ were thought to substitute the Al3+ octahedral sites. The red emission peaks derived from d–d transitions of the Mn4+ (3d3) configuration from 2E to 4A2 were observed around 670 nm. The emission intensity increased consistently with the Mn-doping concentration, and the highest intensity was achieved at the Mn-doping of 0.10 mol. At and above 0.10 mol Mn-doping, the concentration quenching was observed. Based on these results, the relationships between the crystalline phases of the LiAlO2 phosphor matrix, amount of the doped-manganese, and the photoluminescence properties were discussed from a viewpoint to develop a novel α-LiAlO2:Mn4+ red phosphor.