Analysis of Ce³⁺ luminescence quenching in solid solutions between Y₃Al₅O₁₂ and Y₃Ga₅O₁₂ by temperature dependence of photoconductivity measurement

Photocurrent excitation spectra were measured to investigate the quenching in the garnet solid solutions. Intense photocurrent excitation bands attributed to the lowest 5d₁ and the second lowest 5d₂ levels were observed in the Ce-doped Y₃Al₂Ga₃O₁₂ (Ce:YAGG) and Y₃Ga₅O₁₂ (Ce:YGG). Based on the results of temperature dependence of photoconductivity, the 5d₁ and 5d₂ levels in the Ce:YAGG are found to be located below and within the conduction band, respectively, while both levels in the Ce:YGG are found to be located within its conduction band located at lower energy levels. In addition, the threshold of photoionization from the 4f level of Ce³⁺ to the conduction band in the Ce:YAGG and Ce:YGG were estimated to be 3.2, and 2.8 eV, respectively. We conclude that the main quenching process in the Ce:YAGG is caused by the thermally stimulated ionization process with activation energy of 90 meV from the 5d₁ to the conduction band, and that in the Ce:YGG is caused by the direct ionization process from the 5d levels to the conduction band.