Sr4B_(10)O_(18)(OH)2-2H2O: a new UV nonlinear optical material with a [B_(10)O_(23)]~(16-) building block

摘要

A new ultraviolet (UV) nonlinear optical (NLO) crystal Sr4B_(10)O_(18)(OH)2-2H2O has been synthesized using the hydrothermal method. It crystallizes in the triclinic space group PI (no. 1) with lattice constants a = 6.4991(6) A, b = 6.5059(6) A, c = 11.3175(11) A, a = 88.458(6)°, 0 = 86.019(5)°, y = 61.351(5)°, Z = 1. The fundamental building block of the structure is a [B_(10)O_(23)]~(16-) unit which consists of two stereo-isomeric configurations of [B5O_(12)]~(9-) groups. The structure exhibits a ∞[B_(10)O_(18)]~(6-) three dimensional network with 9-membered tunnels along the b-axis where the Sr cation, OH anion and H20 molecule are located. Powder second harmonic generation (SHG) measurements indicate that Sr4B_(10)O_(18)(OH)2-2H2O is type-l phase-matchable and displays a SHG response of about 2 x KH2PO4. The UV-Vis-NIR diffuse reflectance spectrum shows that its cutoff edge is lower than 190 nm. Density functional theory (DFT) calculations on electronic structures and SHG coefficients confirm the experimental results.