Defect Structure and Upconversion Luminescence Properties of LiNbO3 Highly Doped Congruent In:Yb:Ho:LiNbO3 Crystals

Abstract

Congruent In:Yb:Ho:LiNbO3 crystals with different In3+ concentrations have been grown by Czochralski method. Red and green upconversion emissions were observed under 980 nm excitation at room temperature. The effect of In3+ on the upconversion luminescence was studied in association with the defect structure caused by In3+ doping. Infrared transmission spectra indicate a clear shift of the OH− absorption peak along with an increase of doped In3+ concentrations, owing to the occupation of InLi2+ blow the threshold concentration (3%) that suppresses the NbLi4+ defects, and the occupation of InNb2− and InLi2+ above the threshold. Moreover, In3+ induced upconversion luminescence intensity changes were observed to be consistent with the measured lifetime and the OH group content changes, manifesting the highest upconversion luminescence at In3+ concentration of 1 mol%. Mechanistic investigations indicated that both the green (at 548 nm) and the red (666 nm) emissions involve two-photon processes, being ascribed to two sequential energy transfers from to the excited Yb3+ ions to the Ho3+ ions. These results suggests that In:Yb:Ho:LiNbO3 crystals provide opportunities for strong short wavelength up conversion lasers and related laser devices.