Abstract
Defect structure of nominally pure lithium niobate crystals grown from a boron doped charge have been studied by Raman and optical spectroscopy, laser conoscopy, and photoinduced light scattering. An influence of boron dopant on optical uniformity, photoelectrical fields values, and band gap have been also studied by these methods in LiNbO3 crystals. Despite a high concentration of boron in the charge (up to 2 mol%), content in the crystal does not exceed 10−4 wt%. We have calculated that boron incorporates only into tetrahedral voids of crystal structure as a part of groups [BO3]3−, which changes O–O bonds lengths in O6 octahedra. At this oxygen–metal clusters MeO6 (Me: Li, Nb) change their polarizability. The clusters determine optically nonlinear and ferroelectric properties of a crystal. Chemical interactions in the system Li2O–Nb2O5–B2O3 have been considered. Boron, being an active element, structures lithium niobate melt, which significantly influences defect structure and physical properties of a crystal grown from such a melt. At the same time, amount of defects NbLi and concentration of OH groups in LiNbO3:B is close to that in stoichiometric crystals; photorefractive effect, optical, and compositional uniformity on the contrary is higher.
Highlights
IntroductionLithium niobate (LN, LiNbO3 ) attracts attention due to its possible applications in integral and nonlinear optics, pure optics (generation of optical harmonics, lasing parametric generation, electro-optics, optical amplification, and conversion of optical radiation), acoustoelectronics (bandpass filters and SAW delay lines), quantum electronics, and solid state physics [1,2,3,4]
Lithium niobate (LN, LiNbO3 ) attracts attention due to its possible applications in integral and nonlinear optics, pure optics, acoustoelectronics, quantum electronics, and solid state physics [1,2,3,4]
Our studies have shown that the fraction of the melt, the crystallization of which leads to the production of an optically uniform LiNbO3 :B crystal, does not exceed 17–18% [19,25]
Summary
Lithium niobate (LN, LiNbO3 ) attracts attention due to its possible applications in integral and nonlinear optics, pure optics (generation of optical harmonics, lasing parametric generation, electro-optics, optical amplification, and conversion of optical radiation), acoustoelectronics (bandpass filters and SAW delay lines), quantum electronics, and solid state physics [1,2,3,4]. The equipment associated with modern optoelectronic and telecommunication technologies often includes LN crystals. Such applications claim LN crystals with high optical uniformity and optical damage resistance. Doping by a wide spectrum of metal elements is possible due to an octahedral coordination of metal ions in the LN structure. At this a significant preserving symmetry distortion of MeO6 (Me: Li+ , Nb5+ , dopant) octahedra can occur [1,2,7].
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