Hydrothermally grown borate single crystals for deep ultraviolet and nonlinear optical applications

摘要

Acentric lanthanide borates of the formula LnBO_3 (Ln = La-Lu, Y) as well as acentric tetragonal LiBO_2 were grown as high quality' single crystals from hydrothermal solutions. The crystals are candidates for nonlinear optical applications as well as host materials for laser active ions. The materials are thermally' stable up to at least 1000 deg C and their crystal structure is found using x-ray diffraction to be acentric as was corroborated by' the observance of second harmonic generated light. LnBO_3 crystallises in the orthorhombic space group, Cmc2_1, with lattice parameters: a=5.115(1) A, b = 8.269(2) A, c=5.881(1) A, unit cell volume, V=248.76(9) A~3 and atoms per unit cell, Z=4. The smaller lanthanides (Sm-Lu, Y) of the series LnBO_3 crystallise in the acentric space group R32. This known phase has mainly been studied as powder but the crystal growth and characterisation of them are reported. The compound LiBO_2 crystallises in the tetragonal space group I-42d with a unit cell of a=4.1987(6) A, c=6.5139(13) A, V=114.83(3) A~3, Z=4. Absorption and luminescence spectra of the borates are given, providing corroboration that these materials have bandgaps above 5 e V and are of interest for deep ultraviolet light sources through direct emission or through self frequency doubling of visible emissions.