Two-photon excited luminescence of thulium-activated lanthanum oxysulfide (La2O2S–Tm3+)

Abstract
Using the results from two-photon excitation experiments it is shown that a low lying FC shifted state is present in La2O2S–Tm3+. The thermal quenching of the 1I6 emissions can be explained in terms of thermally promoted crossovers to this FC shifted state.