Growth and properties of Zn, Co Co-doped near-stoichiometric LiNbO3 crystal

Near-stoichiometric LiNbO3 single crystals doped with 0.5mol% Co2+ and co-doped with Co2+ in 0.5mol%and Zn2+ in 3 mol% and 6 mol% (designated SLN0, SLN3, SLN6, respectively) in the raw compositions were grown by the Bridgman method under the conditions of taking K2O as flux. The absorption spectra and emission spectra of upper and lower parts of crystals were measured. The absorption spectra showed the characteristic of Co2+ in octahedral co-ordination, and four absorption peaks at 520 nm, 549 nm, 612 nm, 1447 nm were observed in all the obtained crystals. However, the absorption intensity had an obvious change with the content of ZnO dopant. A sharp emission peak at 776 nm was observed under excitation of 520 nm light, and the emission intensity was also associated with the doping content of ZnO. The contents of Li2O were estimated from the absorption edge of SLN0, SLN3 and SLN6 to be 49.06 mol%, 49.28 mol% and 49.1 mol%. The doping content of ZnO takes great effects on the distributing concentration of Co2+ in LiNbO3 crystal. When 3% of ZnO in mole fraction is doped, the Co2+ are suppressed effectively to enter LiNbO3 crystal sites, and the effect becomes weaker while the dopant of ZnO reaches to 6% mole fraction. The reasons for the concentration changes of Co2+ and spectra change can be interpreted by the suppressing effect of ZnO on the incorporation of Co2+ions and the change of distribution coefficient of Zn2+ as its incorporating content.