Na2CsBe6B5O15: an alkaline beryllium borate as a deep-UV nonlinear optical crystal.

A new deep-UV nonlinear optical crystal, Na(2)CsBe(6)B(5)O(15), has been grown through spontaneous crystallization with a molten flux based on Na(2)O-Cs(2)O-B(2)O(3). Na(2)CsBe(6)B(5)O(15) contains two-dimensional alveolate beryllium borate layers [Be(2)BO(5)](∞) that are bridged via planar [BO(3)] groups. UV-vis diffuse reflectance analysis on a powder sample of Na(2)CsBe(6)B(5)O(15) indicates that the short-wavelength absorption edge of Na(2)CsBe(6)B(5)O(15) is below 200 nm. Second-harmonic generation (SHG) on the powder sample was measured with a 1064 nm laser using the Kurtz and Perry technique, which showed that Na(2)CsBe(6)B(5)O(15) is a phase-matchable material, and its measured SHG coefficient is ~1.17 times as large as the d(36) coefficient of potassium dihydrogen phosphate. The relatively larger SHG coefficient of Na(2)CsBe(6)B(5)O(15) originates from its shorter distance between the adjacent layers bridged via the small [BO(3)] groups.