Jahn‐Teller Effect in EPR and Optical Absorption Spectra of Cu²⁺ in LiNbO₃ Single Crystals

Abstract

Abstract Optical and EPR spectra of LiNbO 3 single crystal doped with copper ions are measured in the range of 200 to 6000 nm and in the X‐band, respectively. In the temperature range 60 to 200 K a transition is observed from the low‐temperature EPR spectra with C s symmetry ( g 𝒵 = 2.403, g y = 2.121, g x = 2.095 and = 51°) to the high‐temperature spectrum with C 3v symmetry ( g ′ ∥ = 2.22, g ⟂ = 2.17 and 𝒵 ∥ C 3 ) whose parameters are given by the average of the corresponding parameters of the low‐temperature spectra. EPR spectra of LiNbO 3 :Cu 2+ are interpreted taking account of the static Jahn‐Teller effect in trigonal field and formation of non‐equivalent minima on the adiabatic potential surface. In case of the static Jahn‐Teller effect in trigonal field formulas for the g ‐factors of d 9 ions are derived theoretically. A new model of Cu 2+ substitution in LiNbO 3 , i.e. formation of a Cu  V Li complex, is suggested. In optical spectra an absorption band at 5000 cm −1 is detected due to Jahn‐Teller splitting of the 2 E tr ground state. The Jahn‐Teller stabilization energy E JT = 1250 cm −5 and crystal field parameters 10 Dq = 8200 cm −1 , ν = −1200 cm −1 , and ν− = 600 cm −1 are determined.