Up-conversion in Er3+-doped LiNbO3 crystals

Frequency up-conversion luminescence and the excitation spectra of Er3+ ions in LiNbO3 crystals have been studied at room temperature. The observed up-conversion luminescence bands have peaks at about 410, 550 and 670 nm, while the excitation bands have peaks at 774, 749 and 658 nm for the 410 nm luminescence, at 984, 908, 893, 817, 774, 749 and 658 nm for the 550 nm luminescence, and at 984, 908, 893, 817, 774 and 749 nm for the 670 nm luminescence. From a comparison of the excitation-band spectra for the luminescence with the absorption spectra, it is suggested that a two-photon absorption process and an excited state absorption process occur in parallel in the up-conversion. Sharp 410 and 480 nm lines were observed under 820 and 960 nm excitation, respectively. These lines are suggested to be the second harmonic radiation from the nonlinear LiNbO3 bulk crystal. (orig.)