Spectroscopic Studies of SrTiO3Using Impurity-Ion Probes

Abstract

Sharp-line fluorescence and absorption in the region of 7935 Å were observed in ${\mathrm{Cr}}^{3+}$-doped and undoped SrTi${\mathrm{O}}_3$. It is reasonably established that the fluorescence and absorption are due to the ${}_{}{}^2{}_{}{}^{}E\leftrightarrow {}_{}{}^4{}_{}{}^{}A_2^{}{}_{}{}^{}$ transition ($R$ line) of the ${\mathrm{Cr}}^{3+}$ ion. Polarization and absorption measurements indicate that the $R$-line transition is magnetic dipole. Fluorescence from ${\mathrm{Mn}}^{4+}$-doped SrTi${\mathrm{O}}_3$ was seen at about 7230 Å. At low temperatures, a temperature-dependent splitting of the $R$-line transition of ${\mathrm{Cr}}^{3+}$ is seen. It is shown that this is due to the lifting of the degeneracy of the ${}_{}{}^2{}_{}{}^{}E$ state by the temperature-dependent tetragonal field present in SrTi${\mathrm{O}}_3$ below 103±2°K. These results are compared with previous measurements on rare-earth ions in SrTi${\mathrm{O}}_3$. The possible origin of the tetragonal transition is discussed.