Low symmetry centers in LiNbO3 doped with Yb and Er

Electron paramagnetic resonance spectroscopy studies of LiNbO3 single crystal doped with 1 wt% of Yb3+ and 0.1 wt% Er are reported. Additionally, Raman spectra of the following crystals are presented: LiNbO3:Nd, Yb (0.5 wt%, 0.7 wt%), LiNbO3:Nd, Mg (2 wt%, 6 wt%), and LiNbO3:Er (0.3 wt%). Raman spectra have revealed bands in the 50–220 cm−1 range, suggesting the presence of localized phonons. The localized phonons may be considered as indirect evidence of local perturbations around Yb/Er ions, possibly due to formation of Yb/Er ion pairs. EPR spectra are interpreted basing on this presumption using a spin Hamiltonian for the Yb3+ dissimilar ion pairs. This model explains the observed spectral features, apparently due to the C1 symmetry of Yb ions. In the case of the LN:Er sample, the angular dependence of EPR lines enabled distinguishing the presence of several non-equivalent centers. After deconvolution of the main EPR line into several Lorentzian components, the Er3+ center with the lowest C1 point group symmetry was resolved and values of the g tensor were estimated.