Time- and temperature-resolved luminescence spectroscopy of LiAl4O6F:Mn red phosphors

Ceramic samples of LiAl4O6F phosphors doped with 1.0 mol. % manganese ions have been synthesized by high-temperature solid-state reaction technique and investigated as possible red-emitting light converters. It has been found that the emission spectrum of LiAl4O6F:Mn phosphors consists of a narrow band peaked at 661 nm and a broader band peaked in the region of 675 ÷ 720 nm depending on synthesis conditions. The intensity of the latter band increases and the peak of this band shifts to longer wavelengths with increasing the fraction of MgF2 used as a flux material. Besides that, these two emission bands have strongly different decay times, namely τ1 ~ 240 μs and τ2 ~ several ms, respectively. The decay kinetics and time-resolved spectra of these two emission components have been studied in the temperature range of 10 ÷ 290 K under pulsed laser excitation at 262 nm. The observed luminescence properties have been analyzed within a model which considers the presence of manganese ions having different valence states (Mn4+ and Mn2+) in the specific spinel-type crystal structure of the LiAl4O6F host matrix, which provides many possibilities for different local environment near the doping manganese ions.