Phosphorescence of Ce-doped Gd₃Al₂Ga ₃O₁₂ crystals studied using luminescence spectroscopy

Photoluminescence (PL) and thermally stimulated luminescence (TSL) properties of Ce-doped Gd₃Al₂Ga₃O₁₂ (Ce:GAGG) crystals have been studied in the temperature range of 10-300 K under electron excitation from the 4f level to the 5d levels of Ce³⁺ ions. PL and TSL spectra commonly exhibit a prominent band around 2.31 eV, due to electron transitions from the lowest 5d (5d₁) level to the 4f levels. The intensity of the Ce³⁺ PL band is significantly changed with temperature under excitation from the lowest 4f level to a higher-lying 5d (5d₂) level, whereas it is scarcely changed under excitation from the 4f level to the 5d₁ level. Such change correlates well with the appearance of TSL glow peaks at 84 and 175 K. The luminescence properties are apparently influenced by the thermal behavior of electrons trapped at some lattice site, but not by nonradiative processes of electrons starting from the 5d₁ level. The phosphorescence process will be discussed using a phenomenological model based on the results obtained.