Influence of In2O3 codoping on the upconversion emission properties of Er3+-doped near-stoichiometric LiNbO3 crystals

Two near-stoichiometric lithium niobate (NSLN) crystals codoped with Er3+(1 mol%) and In3+ (0 and 0.3 mol%) were grown from Li-rich melt ([Li]/[Nb]=1.38, molar ratio) by the conventional Czochralski method. The Er, In contents and [Li]/[Nb] ratios in the crystals were measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES). The OH− absorption spectra were investigated to characterize the defect structure of the crystals. The optical damage resistance ability was characterized by the transmission facula distortion method. The results indicate that the optical damage resistance ability is enhanced by one order of magnitude for Er:NSLN codoped with 0.15 mol% In2O3. The electronic transitions of Er3+ ions were analyzed based on ultraviolet-visible absorption spectra. The upconversion fluorescence spectra excited by an 800 nm femtosecond laser were measured at room temperature. The results show that three emission peaks centered at 535, 551 and 673 nm exist in both crystals and the intensities at these three peaks of In:Er:NSLN are larger than those of Er:NSLN, but an additional 400 nm peak appears in In:Er:NSLN. The 400 nm emission peak is verified experimentally to be the second harmonic generation of 800 nm light.