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

Optical and EPR spectra of LiNbO3 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 Cs symmetry (g𝒵 = 2.403, gy = 2.121, gx = 2.095 and = 51°) to the high‐temperature spectrum with C3v symmetry (g′∥ = 2.22, g⟂ = 2.17 and 𝒵 ∥ C3) whose parameters are given by the average of the corresponding parameters of the low‐temperature spectra. EPR spectra of LiNbO3:Cu2+ 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 d9 ions are derived theoretically. A new model of Cu2+ substitution in LiNbO3, i.e. formation of a Cu  VLi complex, is suggested. In optical spectra an absorption band at 5000 cm−1 is detected due to Jahn‐Teller splitting of the 2Etr ground state. The Jahn‐Teller stabilization energy EJT = 1250 cm−5 and crystal field parameters 10Dq = 8200 cm−1, ν = −1200 cm−1, and ν− = 600 cm−1 are determined.