Temperature Dependence of Luminescence and Decay Time under Optical Excitation from Li_6Gd(BO_3)_3:Ce Single Crystals

The temperature dependence of luminescence and decay time under optical excitation from Li6Gd(BO3)3:Ce single crystals was investigated in the temperature range of 80-500K. The Ce3+ emission under the direct Ce3+ excitation (346nm) shows the temperature dependence different from that under the Gd3+ excitation (274nm). The former is governed mainly by the thermal quenching effect and the later is determined collectively by the energy transfer from Gd3+ to Ce3+ and the thermal quenching of the Ce3+ emission. Below 200K, the luminescence intensity under the 274nm excitation is enhanced with the temperature, which is attributed to the increase of the energy transfer rate from Gd3+ ions to Ce3+ ions. Beyond 200K, the luminescence intensity under the 274nm excitation is dominated mainly by the thermal quenching effect and decreases with the temperature. Decay times at different temperatures from 80K to 500K were measured and two distinct decay changing trends were observed. The decay time increases slightly with the temperature below 225K, which is ascribed to a photon trapping effect. Beyond 225K, the decay time reduces gradually when the temperature is increased, which is caused by the increase of the non-radiative relaxation rate. The activation energy calculated by using the classical thermal quenching equation, 0.33eV matches well with that deduced by using the Arrhenius law, 0.32eV.