Improvement of persistent phosphorescence of Ca0.9Sr0.1S : Bi3+ by codoping Tm3+

Persistent phosphors Ca0.9Sr0.1S : 0.01Bi3+ and Ca0.9Sr0.1S : 0.01Bi3+,0.01Tm3+ were prepared via solid chemical reactions at 1200°C. Luminescence, excitation spectra, decays of afterglow and thermoluminescence were investigated. Blue persistent phosphorescent band of 3P1–1S0 transition of Bi3+ was observed at 453 nm with Stoke’s shift of 45 nm. The influence of codoping of Tm3+ on phosphorescence was studied. It was found that adding Tm3+ to the mixed sulfide host created a new trapping center, and the brightness and the persistent time of the phosphor were improved by more than 35%.