Er ³⁺ diffusion in LiTaO ₃ crystal

Some Er ³⁺ -doped LiTaO ₃ plates were prepared by in-diffusion of Er-metal film locally coated onto congruent Z-cut substrate in air at a wide temperature range from 1000 to 1500 °C. After diffusion, Er ³⁺ -doping effect on LiTaO ₃ refractive index and Li ₂ O out-diffusion arising from Er ³⁺ in-diffusion were studied at first. Refractive indices at the doped and undoped surface parts were measured by prism coupling technique and the surface composition was estimated. The results show that Er ³⁺ dopant has small contribution to the LiTaO ₃ index. Li ₂ O out-diffusion is slight (Li ₂ O content loss <0.3 mol%) for the temperature below 1300 °C while is moderate (Li ₂ O content loss <0.6 mol%) for the temperature above 1400 °C. The Er ³⁺ profile was studied by secondary ion mass spectrometry. The study shows that the diffused Er ³⁺ ions follow either a complementary error function or a Gaussian profile. Characteristic parameters including diffusivity, diffusion constant, activation energy, solubility, solubility constant and heat of solution were obtained and compared with the LiNbO ₃ case. The comparison shows that the diffusivity and solubility in LiTaO ₃ are considerably smaller than in LiNbO ₃ because of the difference of Ta and Nb in atomic weight.