Concentration determination of er³⁺ in LiNbO₃ Crystal by absorption spectroscopy

A number of X-, Y-, and Z-cut congruent or near-stoichiometric only Er ³⁺-doped or Er³⁺/Dⁿ⁺-codoped (D ⁿ⁺=Mg²⁺, Zn²⁺, In³⁺, Yb ³⁺) LiNbO₃ crystals were grown by the Czochralski method. The Er³⁺ concentrations in these crystals were determined at first from neutron activation analysis. Then, the integrated unpolarized Er ³⁺ absorption coefficient at the 1.5 μm wavelength region was measured as a function of Er³⁺ concentration in crystal. The results show that the integrated absorption coefficient (IAC) is linearly proportional to the Er³⁺ concentration in the crystal ([Er³⁺] _crystal) whether the crystal is only Er³⁺-doped or Er ³⁺/Dⁿ⁺-codoped, and the fitted expression is IAC=(95.0±4.6)·[Er³⁺]_crystal for the X- or Y-cut crystals and IAC=(102.0±5.1) ·[Er³⁺]_crystal for the Z-cut ones. These linear expressions enable to establish an optical method used to accurately determine Er³⁺ concentration in any only Er³⁺-doped or Er³⁺/Dⁿ⁺-codoped LiNbO₃ crystal from the simple and rapid unpolarized absorption measurement, and the error is within 10%.