Site Occupancies, Luminescence, and Thermometric Properties of LiY(SiO)O:Ce Phosphors.

In this work, we report the tunable emission properties of Ce in an apatite-type LiY(SiO)O compound via adjusting the doping concentration or temperature. The occupancies of Ce ions at two different sites (Wyckoff 6h and 4f sites) in LiY(SiO)O have been determined by Rietveld refinements. Two kinds of Ce f-d transitions have been studied in detail and then assigned to certain sites. The effects of temperature and doping concentration on Ce luminescence properties have been systematically investigated. It is found that the Ce ions prefer occupying Wyckoff 6h sites and the energy transfer between Ce at two sites becomes more efficient with an increase in doping concentration. In addition, the charge-transfer vibronic exciton (CTVE) induced by the existence of free oxygen ion plays an important role in the thermal quenching of Ce at 6h sites. Because of the tunable emissions from cyan to blue with increasing temperature, the phosphors LiY(SiO)O:Ce are endowed with possible thermometric applications.