Optical characteristics of Er3+ ion in Er/Yb:LiNbO3 crystal: Comparison with the dissimilar effect of anti-photorefractive ions Zn2+, In3+ and Zr4+

The different influences of Zn2+, In3+ and Zr4+ ions on the optical characteristics of Er3+ ion in Er/Yb:LiNbO3 crystals were discussed. An enhanced 1.54 μm emission was observed for Zr/Er/Yb:LiNbO3 crystal, but the Zn2+ tri-doping resulted in a decreased one, and the intensity of 1.54 μm emission remained about same in In/Er/Yb:LiNbO3 crystal. The populations of the green emitting 4S3/2/2H11/2 states were achieved through the three-, two- and two-phonon processes in Zn/Er/Yb:LiNbO3, In/Er/Yb:LiNbO3 and Zr/Er/Yb:LiNbO3 crystals, respectively. Zn2+ and In3+ ions affected the optical characteristics of Er3+ ion via modifying the Er3+ ion occupancy in Er/Yb:LiNbO3 crystal. The formation of ErLi2+–ErNb2− ion pairs caused by the Zn2+ and In3+ ions could increase the rate of cross relaxation process. The OH− absorption spectra showed that the incorporation of Zr4+ ions increased OH− content, which increased the probability of the nonradiative relaxation process of 4I11/2→4I13/2 (Er) in Zr/Er/Yb:LiNbO3 crystal. The J–O intensity parameters Ωt (t=2, 4 and 6), the radiative lifetime (τrad) and fluorescence branching ratio (β) in Zr/Er/Yb:LiNbO3 crystal were predicted by Judd–Ofelt theory. Füchtbauer–Ladenburg and McCumber methods were carried out to calculate the emission cross-sections at 1.54 μm emission. The gain cross-section, estimated as a function of the population inversion ratio, allowed us to evaluate a potential laser performance of Zr/Er/Yb:LiNbO3 crystal. -- Highlights: •The different effect of anti-photorefractive ions on Er/Yb:LiNbO3 crystal. •Zn2+ and In3+ affect the rate of cross relaxation process. •Zr4+ ion increases the nonradiative relaxation of 4I11/2→4I13/2. •The Judd–Ofelt intensity parameters are discussed. •The absorption and emission cross-section at 1.54 μm are calculated