Emission characteristics of Er3+ in vapor-transport-equilibrated Er/Zn-codoped LiNbO3 crystals

Polarized visible and infrared emission characteristics of Er3+ ions in vapor-transport-equilibration (VTE)-treated LiNbO3 crystals codoped with different concentrations of Zn and Er were investigated in comparison with corresponding as-grown crystals. The results show that the VTE treatment leads to substantial spectral changes of Er3+ emissions at 0.65, 0.98 and 1.5 μm regions, and the spectral changes in the 0.98 and 1.5 μm regions appear to be Zn-concentration-dependent. It is concluded in combination with X-ray powder diffraction results and optical absorption characteristics reported previously that the VTE treatment resulted in crystalline phase transformation with respect to Er3+ ions from original LiNbO3 to ErNbO4 phase in all crystals studied. The formation of the ErNbO4 phase and the Zn2+ codopants are responsible for the VTE-induced substantial spectral changes. The emission characteristics of the ErNbO4 precipitates in the Zn/Er-codoped crystals are found to be very different from those of the ErNbO4 precipitates in the only Er-doped crystal in the infrared region, and the difference is attributed to the influence of the Zn2+ codopant on the Er3+ ion environment. The mechanism of the crystalline phase transformation is qualitatively explained from the viewpoint of the declined solubility of Er3+ ion in a Li-rich LiNbO3 crystal and from the phase diagram of Li2O-Nb2O5 system.