Er3+ diffusion in congruent LiNbO3 crystal doped with 4.5 mol % MgO.

Standard thermal diffusion of Er³⁺ into X-cut congruent LiNbO₃ crystal with the MgO doping level close to the antiphotorefractive threshold concentration, 4.5 mol%, was attempted at the temperature close to Curie point of the crystal. Single-crystal x-ray diffraction, photoluminescence spectroscopy and secondary ion mass spectrometry (SIMS) were used to study the crystalline phase with respect to Er³⁺ ions and the depth profile of the diffused Er³⁺ ions. The results show that the thickness of the Er metal film coating should not be thicker than 4.6 nm. In this case, the diffusion is complete, the diffused surface is clean, and the Er³⁺ ions in the diffused layer still retain the LiNbO₃ phase. On the other hand, the diffusion will be incomplete if the initial thickness of the Er metal film is thicker than 4.6 nm. The residual Er³⁺ ions form ErNbO₄ grains on the surface of the crystal. SIMS analysis shows that the diffused Er³⁺ ions follow a monoexponential decay profile. The experimental results also show that the diffusivity of Er³⁺ in the X-cut congruent Mg(4.5 mol %):LiNbO₃ is similar to 4.69×10^-3 μm²/h at 1130 °C. Further vapor transport equilibration treatment following the standard diffusion procedure results in transformation of the diffused Er³⁺ ions from LiNbO₃ into the ErNbO₄ phase and, hence, substantial spectral change of the 1.5 μm emission. [ABSTRACT FROM AUTHOR]