OH- absorption of zn-doped LiNbO3 single crystals after proton exchange

An investigation of the OH- absorption spectra of Zn-doped LiNbO3 single crystals with doping concentrations from 0.0 to 8.3mol% after proton exchange.(PE) is carried out. Before PE treatment, the absorption bands are found centered at approximately 3485 cm(-1) for the samples with Zn-doping concentrations below 7.5 mol%, whereas two distinct bands at 3505, and 3530 cm(-1) are clearly observed for the samples with Zn-doping concentrations above 7.5 mol%. After PE treatment, an absorption band at 3505 cm(-1) is predominant for all the samples, and this is attributed to the high concentration of H+ ions substituting Li atoms. However, for the highly Zn-doped samples, the lineshape and intensity of the 3530 cm-1 mode remain the same during PE. A theoretical investigation using the hybrid density functional B3LYP method with a simple cluster structure shows that the origins of the 3485 and 3530 cm(-1) absorption modes correspond to the Li- and Nb-vacancy models, respectively.