Room temperature absorption spectra analysis of Er ³⁺/Yb ³⁺-doped hydrothermal epitaxial layer on LiNbO ₃ and LiTaO ₃ single crystal substrates

In this paper we introduce the undetermined parameter k _NL which is related to the concentration and thickness, and perform the fitting calculation that is on the basis of the absorption spectrum about the hydrothermal epitaxial polycrystalline sample on the surfaces of LiNbO ₃ and LiTaO ₃ doped with Er ³⁺/Yb ³⁺ single crystalline substrates according to the J-O theory at the room temperature. It is obtained that for LiNbO ₃ Ω ₂ = 2.34×10 ^-20 cm ², Ω ₄ = 0.77×10 ²⁰ cm ², Ω ₆ = 0.31×10 ^-20 cm ², and k _NL = 4.32×10 ^-2 mol·m ^-2 and for LiTaO ₃ Ω ₂ = 1.68×10 ^-20 cm ², Ω ₄ = 0.84×10 ^-20 cm ², Ω ₆ = 0.45×10 ^-20 cm ², and k _NL = 9.17×10 ^-3 mol·m ^-2. This method can be extended to the systems in which the data of concentration and thickness such as powder or colloid are difficult to obtain. According to the up-conversion luminescence analysis and the calculation via spectrum parameters, it is confirmed that both the samples have the green up-conversion luminescence at Er ³⁺:Yb ³⁺ = 1:1, the method of reducing the energy of matrix phonon is tried to improve the quantum cutting yield of ⁴I _13/2 to ²H _11/2 and ⁴S _3/2.