Luminescence and optical absorption spectra of heavily Mg-doped LiNbO₃ single crystals irradiated by pulsed electron beam

We report on the luminescence and optical absorption spectra of the congruent LiNbO₃ (LN) and Mg-doped LiNbO₃ (MLN) crystals irradiated by a pulsed electron beam. The luminescence of the LN crystal has an asymmetric wide spectrum band with a maximum around 3.2 eV. The luminescence spectrum of a 10 mol% MgO-doped LiNbO₃ (MLN-10) crystal exhibits a new intensity peak at 2.4 eV due to an antisite defect, namely Mg displaced to into the Nb site (Mg_Nb). The optical absorption spectrum of LN contains four absorption bands of 1.6, 2.5, 3.2, and 3.6 eV. The bands at 2.5 and 3.2 eV are due to the O^2- hole color centers localized nearby cation vacancies, and those of 1.6 and 3.6 eV are due to the electron centers captured by Nb_Li ⁵⁺ antisite defects. The optical absorption spectrum of the MLN-10 crystal displays one supplementary band peaking at 1.0 eV in the infrared region, which is related to the capture of electrons by Mg complexes. The optical density in the hole band rapidly changes with increasing the MgO concentration. The formation efficiency of hole band centers has a maximum value at 6 mol% MgO-doped LiNbO₃ (MLN-6) crystal.