Optical and photoelectrical studies of charge-transfer processes in YAlO3:Ti crystals

The donor and acceptor charge-transfer transitions in YAl${\mathrm{O}}_3$:${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ were investigated through absorption, emission, excitation, one-photon and two-photon photoconductivities, excited-state absorption, and thermoluminescence. The results are contrasted to similar studies previously made on ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$:${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$. The dominant ${\mathrm{Ti}}^{3+}$ population has a photoionization threshold at 37 000 ${\mathrm{cm}}^{-1\mathrm{}}$. The lowest energy ${\mathrm{Ti}}^{4+}$ charge-transfer transition has its zero-phonon energy near to 33 900 ${\mathrm{cm}}^{-1\mathrm{}}$. The sum of these two quantities agrees with the reported band-gap energy of YAl${\mathrm{O}}_3$. The position of the ${\mathrm{Ti}}^{3+}$/${\mathrm{Ti}}^{4+}$ level in the band gap of YAl${\mathrm{O}}_3$ is determined by these measurements. Stimulated emission from the ${}_{}{}^2{}_{}{}^{}E$ state of ${\mathrm{Ti}}^{3+}$ is limited by photoionization from this state.