Optics and Spectroscopy, 2022 Volume 130, Issue 1,Pages 171–183(Mi os1655)
Materials of the International Seminar of the Institute of Spectroscopy of the Russian Academy of Sciences (ISAN), dedicated to the anniversary of Professor M.N. Popova Optical materials
Luminescence properties of non-stoichiometric lithium niobate crystals of various composition and genesis (review)
Abstract:
A brief review of the features of the defect structure and studies of the luminescent properties of nonlinear optical lithium niobate crystals of various compositions and genesis was given. It was established that the electron-hole pair Nb$_{\mathrm{Nb}^{4+}}$–O$^-$ in the oxygen-octahedral cluster NbO$_6$ emitted in the short-wavelength region of the visible spectrum (400–500 nm), while point defects (V$_{\mathrm{Li}}$ and Nb$_{\mathrm{Nb}^{4+}}$–Nb$_{\mathrm{Li}^{4+}}$ bipolarons) – in the long-wavelength region (500–620 nm). At the ratio of Li/Nb $\approx$ 1 the luminescence was extinguished in the visible region of the spectrum due to decreasing the intrinsic luminescence centers. It was shown that the presence of polaron luminescence in the near-IR region (700–1050 nm) was due to the small polarons Nb$_{\mathrm{Li}^{4+}}$ and impurity ions Cr$^{3+}$ localized in lithium and niobium octahedra. The energy transfer between the luminescence centers in the visible and near-IR spectral regions was detected. Moreover, luminescence in near-IR regions was dominant. Doping of LiNbO$_3$ crystals with zinc and magnesium at ZnO $<$ 4.46 mol.% and MgO $<$ 5.29 mol.% led to decreasing luminescence of intrinsic defects (V$_{\mathrm{Li}}$, Nb$_{\mathrm{Nb}^{4+}}$–Nb$_{\mathrm{Li}^{4+}}$). However, there was an increase of the contribution of the short-wave spectrum component at higher dopant concentrations because of the introduction of Zn and Mg into the origin positions of Nb ions.
Keywords:lithium niobate single crystal, point defects, luminescence, luminescence centers.
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