Luminescence quenching and scintillation response in the Ce³⁺ doped Gd_xY_3−xAl₅O₁₂ (x = 0.75, 1, 1.25, 1.5, 1.75, 2) single crystals

The luminescence and scintillation properties of the gadolinium yttrium aluminium garnets, (Gd,Y)₃Al₅O₁₂ doped with Ce³⁺ are investigated as a function of the Gd/Y ratio with the aim of an improved understanding of the luminescence quenching, energy transfer and phase stability in these materials. An increase of both crystal field strength and instability of the garnet phase with increasing content of Gd³⁺ is observed. The instability of the garnet phase results in an appearance of the perovskite phase inclusions incorporated into the garnet phase. The luminescence features of Ce³⁺ in the perovskite phase inclusions and in the main garnet phase are studied separately. The thermal quenching of the 5 d → 4f emission of Ce³⁺ in the latter phase is determined by temperature dependence of the photoluminescence decay time. The results show that the onset of the thermal quenching is moved to lower temperatures with increasing gadolinium content. The measurements of temperature dependence of delayed radiative recombination do not reveal a clear evidence that the thermal quenching is caused by thermally induced ionization of the Ce³⁺ 5d₁ excited state. Therefore, the main mechanism responsible for the luminescence quenching is due to the non-radiative relaxation from 5d₁ excited state to 4f ground state of Ce³⁺. The energy transfer processes between Gd³⁺ and Ce³⁺ as well as between perovskite and garnet phases are evidenced by the photoluminescence excitation and emission spectra as well as decay kinetic measurements. Thermally stimulated luminescence (TSL) studies in the temperature range 77–497 K and scintillation decays under γ excitation complete the material characterization.