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

Some results of the absorption investigations of LiNbO3:Yb3+, Pr3+ (0.8, 0.1 wt.%) and LiNbO3:Yb3+ (1 wt.%) single crystals were made for UV–vis and IR giving evidence on the Yb3+ location at Li+ sites and Pr3+ location at Nb5+ sites. Low temperature absorption measurements have shown the presence of low energy phonons responsible for the intensity shape of the main Yb3+ IR absorption line as a function of the temperature. Raman spectra confirmed the observation.We have observed several paramagnetic centers originating from both isolated Yb3+ and Yb3+ ion pairs. The observed spectral features indicate the Yb centers in both crystals exhibit triclinic C1 symmetry. The temperature dependence of the EPR line intensity and inverse line intensity confirm the presence of coupled Yb3+ ion pairs besides isolated Yb3+ 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 LiNbO3:Yb3+ and LiNbO3:Yb3+, Pr3+ samples, respectively. The presence of co-dopant significantly changes properties of LiNbO3:Yb3+ single crystal. The Pr co-dopant forces the substitution of Yb3+ ions at other possible sites in the host crystal and changes interaction between Yb ion pairs from the antiferromagnetic to ferromagnetic one.