Site Occupancies, Luminescence, and Thermometric Properties of LiY₉(SiO₄)₆O₂:Ce³⁺ Phosphors

Abstract

In this work, we report the tunable emission properties of Ce³⁺ in an apatite-type LiY₉(SiO₄)₆O₂ compound via adjusting the doping concentration or temperature. The occupancies of Ce³⁺ ions at two different sites (Wyckoff 6h and 4f sites) in LiY₉(SiO₄)₆O₂ have been determined by Rietveld refinements. Two kinds of Ce³⁺ f–d transitions have been studied in detail and then assigned to certain sites. The effects of temperature and doping concentration on Ce³⁺ luminescence properties have been systematically investigated. It is found that the Ce³⁺ ions prefer occupying Wyckoff 6h sites and the energy transfer between Ce³⁺ 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 Ce³⁺ at 6h sites. Because of the tunable emissions from cyan to blue with increasing temperature, the phosphors LiY₉(SiO₄)₆O₂:Ce³⁺ are endowed with possible thermometric applications