Epitaxial films (10 to 250μm-thick) of Cr-doped garnet were grown, by means of liquid-phase epitaxy, onto Nd-doped garnet substrates. Co-doping with Mg2+ was used to force Cr4+ formation. Absorption which was characteristic of the Cr4+-doped garnet was found in co-doped films which had been grown at 1000 to 1100C. A very intense absorption band in the ultra-violet region, with a maximum at 275nm, was found for both co-doped and Mg2+-doped epifilms. This was attributed to O vacancies which compensated the excess charge of the Mg2+. Its intensity was related to the Cr4+ content of the film, in that it decreased with increasing amounts of Cr4+ entering the film.

Colour Centres Investigation in Pure and Doped Yttrium Aluminium Garnet Epitaxial Films. S.B.Ubizskii, I.M.Syvorotka, S.S.Melnyk, A.O.Matkovskii: Radiation Effects and Defects in Solids, 2000, 149[1-4], 375-9