Photoionization energies of Cr~(3+) -doped LiNbO+3

摘要

We report on a study of intra-ion and electron transfer transitions in Cr~(3+)-doped LiNbO_3. The energies of the meta-stable emitting levels of Cr~(3+) on both Li and the Nb sites are determined by standard optical spectroscopy techniques. Photoconductive measurements are used to determine the ionization energies of both species of Cr~(3+) ions. From these results, energy level diagrams are created which give the energies of the optically active levels with respect to the host valence and conduction bands. The emitting ~4T_2 level of Cr~(3+) on a Li site and on a Nb site is found to lie 1.5 and 1.2 eV below the, conduction band bottom, respectively. These results lead to the suggestion that the lack of laser action found in LiNbO_3:Cr~(3+) may be due to strong excited state absorption transitions from the meta-stable ~4T_2 level to the host conduction band.