EPR and optical studies of LiNbO3:Yb and LiNbO3:Yb, Pr single crystals

Abstract

Some results of the absorption investigations of LiNbO 3 :Yb 3+ , Pr 3+ (0.8, 0.1 wt.%) and LiNbO 3 :Yb 3+ (1 wt.%) single crystals were made for UV–vis and IR giving evidence on the Yb 3+ location at Li + sites and Pr 3+ location at Nb 5+ sites. Low temperature absorption measurements have shown the presence of low energy phonons responsible for the intensity shape of the main Yb 3+ IR absorption line as a function of the temperature. Raman spectra confirmed the observation. We have observed several paramagnetic centers originating from both isolated Yb 3+ and Yb 3+ ion pairs. The observed spectral features indicate the Yb centers in both crystals exhibit triclinic C 1 symmetry. The temperature dependence of the EPR line intensity and inverse line intensity confirm the presence of coupled Yb 3+ ion pairs besides isolated Yb 3+ ions in both crystals. The EPR line intensity fulfils Curie–Weiss law and yields the antiferromagnetic interaction constant Θ = −0.6 ± 0.3 K and ferromagnetic interaction constant Θ = 2.4 ± 0.1 K for LiNbO 3 :Yb 3+ and LiNbO 3 :Yb 3+ , Pr 3+ samples, respectively. The presence of co-dopant significantly changes properties of LiNbO 3 :Yb 3+ single crystal. The Pr co-dopant forces the substitution of Yb 3+ ions at other possible sites in the host crystal and changes interaction between Yb ion pairs from the antiferromagnetic to ferromagnetic one.