Er³⁺ diffusion in LiTaO₃ crystal

Some Er³⁺-doped LiTaO₃ 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, Er³⁺-doping effect on LiTaO₃ refractive index and Li₂O out-diffusion arising from Er³⁺ 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 Er³⁺ dopant has small contribution to the LiTaO₃ index. Li₂O out-diffusion is slight (Li₂O content loss 2O content loss 3+ profile was studied by secondary ion mass spectrometry. The study shows that the diffused Er³⁺ 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 LiNbO₃ case. The comparison shows that the diffusivity and solubility in LiTaO₃ are considerably smaller than in LiNbO₃ because of the difference of Ta and Nb in atomic weight.