Temperature dependence and quenching characteristics of (La, Gd)${}_2$Si${}_2$O${}_7$ scintillators at various Ce concentrations

Abstract

We investigated the thermal stability of scintillation and the luminescence performances of (La, Gd)${}_2$Si${}_2$O${}_7$ single crystals at various Ce concentrations. We prepared (La${}_{0.25-x}$, Ce${}_x$, Gd${}_{0.75}$)${}_2$Si${}_2$O${}_7$ (x = 0.0001, 0.001, 0.005, 0.01, 0.02, 0.05, and 0.1; unit: molar concentration) single crystals by the Czochralski and micro-pulling-down methods. With increasing Ce concentration, the photoluminescence emission and photoluminescence excitation spectral bands shifted to low energies and the activation energy $\mathrm{\Delta }E$ for thermal quenching decreased. For Ce $<$ 0.5 at.% samples, the photoluminescence emission background value calculated in the exponential approximation started to increase at temperatures greater than 320 K, which is probably because of Ce${}^{3+}$ 5$\text{d}$ excited-state ionization. However, the effect was weaker for the Ce $\ge$ 0.5% samples, which may indicate a comparatively larger contribution from other nonradiative relaxations. Thus the main reason for the thermal quenching of the Ce${}^{3+}$ emission in (La, Gd)${}_2$Si${}_2$O${}_7$ is the combination of the 5$\text{d}$1 excited-state ionization and nonradiative relaxation via thermally excited crossover from the 5$\text{d}$ excited state to the 4$\text{f}$ ground state. The temperature dependence of the scintillation light yield was similar irrespective of the Ce concentration, with Ce 1.0% exhibiting the best performance within the temperature range 300 K to 450 K.

27 pages, 11 figures