A Novel Nonlinear Optical Crystal for the IR Region:  Noncentrosymmetrically Crystalline CsCdBr₃ and Its Properties

Abstract

A noncentrosymmetric crystal structure of CsCdBr(3) has been successfully observed with X-ray single-crystal structure analysis. It crystallizes in the hexagonal space group P6(3)mc, with a = 7.7281(14) A, b = 7.7281(14) A, c = 6.742(2) A, alpha = 90 degrees, beta = 90 degrees, gamma = 120 degrees, Z = 2. It was obtained by a new preparation procedure different from that reported in the literature that gave a centrosymmetric structure. The structure contains Cd-Br octahedrons, which are connected in a plane-sharing way to form one-dimensional long chains. Each octahedron is slightly distorted, as the three Cd-Br bond lengths are 2.774 A, while the other three Cd-Br bond lengths are 2.804 A. The distortion directions of all of the octahedrons are almost parallel and give rise to the accumulation of the microcosmic nonlinear optical (NLO) coefficient. The Kurtz powder technique shows that CsCdBr(3) has a powder second harmonic generation of about 2 times as large as that of potassium dihydrogen phosphate (KDP). It shows excellent transparency in the visible and infrared regions. The thermal stability is also good. Therefore it may be utilized as a potential nonlinear optical crystal for the IR region.