Optical Absorption and Luminescence of $Gd_{3}Ga_{5}O_{12}:Cr,Mg$ Epitaxial Films

The optical absorption, emission spectra and luminescence decay kinetics under photoexcitation of $Gd_{3}Ga_{5}O_{12}$ (GGG) garnet epitaxial films doped with $Cr^{3+}$ ions and co-doped with $Cr^{3+}$ and $Mg^{2+}$ ions have been investigated. Luminescence of the GGG:Cr films due to $\text{}^{4}T_{2}$ → $\text{}^{4}A_{2}$ and $\text{}^{2}E$ → $\text{}^{4}A_{2}$ transitions in $Cr^{3+}$ ions have been observed. Increase of the activator ions concentration has an influence on the intensity and decay time of $Cr^{3+}$ ions photoluminescence. Introduction of the magnesium ions leads to partial transformation of chromium valence state $(Cr^{3+} \rightarrow Cr^{4+})$ and to the appearance of a broad absorption band with the maximum at 860 nm. The narrow lines with luminescence maxima at 704 and 706 nm have arisen in the highly doped GGG:Cr,Mg films.