Influence of vapor transport equilibration on spectroscopic properties of Er:LiNbO3 crystal heavily codoped with MgO.

Z-cut MgO heavily codoped (6 mol %) Er(0.4 mol %) :LiNbO₃ crystals were thermally treated at 1110 and 1120 °C over 100, 120, and 220 h using vapor transport equilibration (VTE) technique. Visible and infrared-absorption and x-ray powder diffraction have been used to characterize their spectral, spectroscopic, and crystalline phase characteristics in comparison with the as-grown crystal. The experimental results show that VTE treatment results in the reduction of background absorption and 4-5-nm blueshift of the optical-absorption edge, qualitatively showing that these crystals have been brought closer to stoichiometric composition. The VTE procedure also results in remarkable Er³⁺ absorption changes. These spectroscopic changes imply that the VTE treatment may result in the formation of ErNbO₄ precipitates in all VTE crystals. In addition, the VTE treatment also results in substantial spectral changes with respect to OH- absorption. These OH- spectral changes are explained from the viewpoint of VTE-induced site-occupancy alterations of intrinsic and extrinsic defects. Based upon the measured absorption spectra, the influences of VTE treatment on the Er³⁺ spectroscopic parameters were studied by using the Judd-Ofelt (JO) theory. The theoretical results show that VTE treatment has a little influence on the branch ratio, and a substantial influence on JO parameters and electron transition probability because of the phase transformation with respect to Er³⁺. The VTE treatment results in the increase of the JO parameters by more than 50% and theoretical radiative lifetime by 50%-120%. [ABSTRACT FROM AUTHOR]