Photoluminescence of Cr3+ in β-Ga2O3 and (Al0.1Ga0.9)2O3 under pressure

The effects of pressure on single crystals of Cr-doped gallium oxide (β-Ga2O3:Cr3+) and aluminum gallium oxide [(Al0.1Ga0.9)2O3] were examined by measuring the wavelength shift in the spectral R lines. Photoluminescence (PL) spectra of these materials were collected from samples in diamond anvil cells at pressures up to 9 GPa. The β-Ga2O3:Cr3+ R lines were found to shift linearly under hydrostatic pressure. The (Al0.1Ga0.9)2O3 R lines also show a linear shift but the R1 line shifted less than for β-Ga2O3:Cr3+. The ratio of R2 to R1 peak areas vs pressure is dominated by nonradiative recombination. X-ray diffraction measurements of (Al0.1Ga0.9)2O3 indicate that its equation of state is similar to that of β-Ga2O3. β-Ga2O3:Cr3+ was examined under non-hydrostatic conditions by using mineral oil as a pressure transmitting medium. Similar to the case in ruby, the R1 line is much more sensitive to non-hydrostatic stress than R2. Spatially resolved PL of a sample at 8 GPa in mineral oil showed significant variations in the R1 emission wavelength. These results suggest that the R1 line can serve as a sensitive probe of alloy composition and non-hydrostatic stress, while the R2 line is insensitive to these perturbations.