Colour centres investigation in pure and doped yttrium aluminium garnet epitaxial films

Abstract

Epitaxial films with thickness of 10–250 μm of yttrium aluminium garnet (YAG) doped with Cr were grown by liquid phase epitaxy technique on YAG: Nd substrateds. Co-doping with Mg²⁺ was used to force the Cr⁴⁺ valent state formation. Dependence of absorption spectra of obtained films on melt-solution composition, growth conditiions and thermal treatment in reducing and oxidizing atmospheres is studied. The absorption being characteristic for YAG:Cr⁴⁺ crystals is found in co-doped films grown at higher temperatures (1000–1100°C). The chromium entering in the tetravalent state is confirmed by the annealing experiments. A very intensive absorption band in UV region with maximum at 275 nm was found both in co-doped and YAG: Mg²⁺ epifilms caused probbly by oxygen vacancies compensating the excess charge of Mg²⁺. Its intensity correlates with Cr⁴⁺ content in the film in the following way: it decreases with Cr⁴⁺ entering in the film.

Key Words:

• Colour centres
• Yttrium aluminium garnet
• Chromium impurity
• Epitaxial film