The optical properties of gadolinium gallium aluminum garnet, Gd-3(Ga,Al)(5)O-12, doped with Ce3+ are investigated as a function of the Ga/Al ratio, aimed at an improved understanding of the energy flow and luminescence quenching in these materials. A decrease of both the crystal field strength and band gap with increasing content of Ga3+ is observed and explained by the geometrical influence of Ga3+ on the crystal field splitting of the 5d level in line with theoretical work of Munoz-Garcia et al. (Munoz-Garcia, A. B.; Seijo, L. Phys. Rev. B 2010, 82, 184118). Thermal quenching results in shorter decay times as well as reduced emission intensities for all samples in the temperature range from 100 to 500 K. An activation energy for emission quenching is calculated from the data. The band gap of the host is measured upon Ga substitution and the decrease in band gap is related to Ga3+ substitution into tetrahedral sites after all octahedral sites are occupied in the garnet material. Based on the change in band gap and crystal field splitting, band diagrams can be constructed explaining the low thermal quenching temperatures in the samples with high Ga content. The highest luminescence intensity is found for Gd-3(Ga,Al)(5)O-12 with 40% of Al3+ replaced by Ga3+.