X-ray diffraction, optical absorption and emission studies on Er3+- and Er3+/Yb3+-doped Li3NbO4 powder

Er3+(/Yb3+)-doped Li3NbO4 powder were prepared by thermally sintering mixtures of Er2O3 (0.5, 1.0 mol%), Yb2O3 (0, 0.5, 1.0 mol%), Li2CO3 (48– 49 mol%) and Nb2O5 (50 mol%) at 1125, 1150 and 1450 C over the durations of 8–22 h. The crystalline phases contained in these samples were determined by using X-ray diffraction and discussed in comparison with a vapor-transport-equilibration-treated (VTE-treated) Er(2.0 mol%):LiNbO3 single crystal and ErNbO4 powder previously reported. The results show that the X-ray patterns of the rare-earth-doped samples reveal little difference each other, but large differences with those of the VTE crystal and ErNbO4 powder. The doped rare-earth ions Er3+ (and Yb3+) present in the powder as the ErNbO4 (and YbNbO4) phase(s). The possibility that the highly Er-doped LiNbO3 crystal contains Li3NbO4 precipitates is small. Optical absorption and emission studies show that the only Er-doped Li3NbO4 powder shows similar absorption and emission characteristics with the pure ErNbO4. The codopant Yb3+ ion enhances the 980-nmupconversion emissions of Er3+ ions, results in remarkable spectral alterations at 0.98 lm region, and causes the alterations of relative absorbance and relative emission intensity of individual peaks or bands at 1.5 lm region. On the other hand, the Yb-codoping hardly affects the Er3+ energy structure and the lifetime of Er3+ ion at 1.5 lm. The measured lifetimes at 1.5 lm of Er3+ ions in the singly Er3+- and doubly Er3+/Yb3+-doped mixtures have a nearly same value of ~ 1.5 ms. For the pure ErNbO4 powder, the lifetime is prolonged to ~2 ms perhaps due to radiation trapping effect.