On possible existence of a new Er centres in LiNbO3:Er, Tm

Electron paramagnetic resonance experiments have been carried out on congruent lithium niobate (LiNbO3) single crystal weakly doped with Er (0.2 wt.%) and codoped with Tm (0.3 wt.%). The EPR lines originating from both the 167Er3+ ions, with a hyperfine structure, as well as from the evenEr3+ ions, are identified. Angular dependence of the EPR lines has allowed distinguishing the presence of several non-equivalent Er3+ centres with the lowest (C1) symmetry. Additionally, some spectral features may indicate the presence of new Er3+ centres with possibly cubic symmetry, however, an alternative explanation is also considered. The model of Er3+ centres and the effects of stoichiometry and codoping on the spectroscopic properties of erbium ions in LiNbO3 crystal are considered.