Experimental and ab initio studies of Cd-5(BO3)(3)Cl: the first cadmium borate chlorine NLO material with isolated BO3 groups

摘要

A nonlinear optical crystal cadmium borate chlorine (Cd-5(BO3)(3)Cl) has been successfully grown through a spontaneous crystallization method. Cd-5(BO3)(3')Cl crystallizes in the noncentrosymmetric space group Cm with isolated BO3 and distorted CdOnClm (n = 4, 5, 7; m = 0, 1, 2) polyhedra. Powder second harmonic generation (SHG) measurements on polycrystalline Cd-5(BO3)(3)Cl indicated that the title compound is phase-matchable in the visible region and exhibits a large SHG response of about 5 x KH2PO4 (KDP). Further optical characterization suggested that the compound has a wide transparent region ranging from UV to near IR with a UV cutoff edge at about 295 nm. In addition, first-principles electronic structure calculations revealed that the macroscopic SHG coefficients of Cd-5(BO3)(3)Cl originate from the cooperative effects of the BO3 groups with asymmetric pi-delocalization, the d(10) cation Cd2+ with the polar displacement and the Cl- anions.