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 $\mathrm{ <}$ 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$\textit{ d}$ 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$\textit{ d}$1 excited-state ionization and nonradiative relaxation via thermally excited crossover from the 5$\textit{ d}$ excited state to the 4$\textit{ f}$ 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.
Categories: cond-mat.mtrl-sci physics.ins-det physics.optics