Features of photoluminescence in lithium niobate crystals doped with zinc in a wide range of concentrations

The concentration changes in the photoluminescence spectra of LiNbO$_{3}$ : Zn crystals (0.004 – 6.5 mol.% ZnO) were studied. It was found that with the increase of zinc concentration from 0.004 to 1.42 mol.% ZnO, the intensity decrease of luminescence bands caused by V$_{\mathrm{Li}}$, Nb$_{\mathrm{Nb}}$, and Nb$_{\mathrm{Nb}}$–Nb$_{\mathrm{Li}}$ defects was observed. As the crystal composition approached the second concentration threshold ($\approx$ 7.0 mol.% ZnO), the luminescent halo shifted by $\approx$ 0.41 eV to the high-energy region of the spectrum and the intensity of the luminescence centers increased at 2.66 and 2.26 eV. It was caused by the appearance of Zn$_{\mathrm{Li}}$ point defects. It was shown that in the LiNbO$_3$ : Zn(4.69 mol.% ZnO) crystal obtained by homogeneous doping technology, there is a greater number of luminescence centers of different origin than in congruent and zinc-doped crystals obtained by direct melt doping technology. In the LiNbO$_3$ : Zn crystal (4.52 mol.% ZnO), the luminescence of the main defects (V$_{\mathrm{Li}}$, Nb$_{\mathrm{Nb}}$, Zn$_{\mathrm{Li}}$) was quenched by increasing the fraction of nonradiative transitions relative to other LiNbO$_3$ : Zn crystals in the concentration range [ZnO] = 4.46 – 6.50 mol.%.