Effect of Ga content on luminescence and defects formation processes in Gd₃(Ga,Al)₅O₁₂:Ce single crystals

Luminescence characteristics of Ce³⁺ - doped Gd₃Ga_xAl_5-xO₁₂ single crystals with different Ga contents (x = 1, 2, 3, 4, 5) are studied in the 9–500 K temperature range. The spectra of the afterglow, photoluminescence, radioluminescence, and thermally stimulated luminescence (TSL) of each crystal coincide. The increase of the Ga content results in the high-energy shift of the spectra while the radioluminescence intensity at 9 K remains practically constant up to x = 4. No Ce³⁺ emission is observed in case of x = 5. The total TSL intensity drastically increases, reaches the maximum value around x = 2–3, and then decreases due to the thermal quenching of the Ce³⁺ emission. The TSL glow curve maxima are gradually shifting to lower temperatures, and the dependence of the maxima positions and the corresponding trap depths on the Ga content is close to linear. However, the activation energy of the TSL peaks creation under irradiation of the crystals in the 4f – 5d₁ absorption band of Ce³⁺ decreases drastically with the increasing Ga content (especially in the range of x = 1–2), and this dependence is found to be strongly nonlinear. Possible reasons of the nonlinearity are discussed.