Optical absorption edge of Mg+Zn:LiNbO3

The optical transmittance of LiNbO3 single crystal double doped with MgO and ZnO was measured from the ultraviolet to the visible range. The wavelength dependence of the absorption coefficient a and its root alpha(1/2) (alpha versus hv and alpha(1/2) versus hv, respectively) were calculated and the characteristics of the absorption edge were discussed. The energy gaps E(g) and E(g)' of the crystals which correspond to the direct transition and the indirect transition, respectively; and the energy of phonons taking part in the indirect transition were calculated. The effects of dopants Mg and Zn on the optical absorption properties are discussed. It was found that the energy E(g)' of our sample which was double doped with MgO and ZnO was smaller than that of congruent LN, causing the indirect transition absorption edge to move towards the infrared.