Specific features of second order optical susceptibilities for a complex borate crystal Bi2ZnB2O7: Experiment and theory

We have synthesized and characterized single-crystal of bismuth borates Bi2ZnB2O7. The results of the experimental measurements and the ab initio theoretical study of the linear and non-linear optical susceptibilities are presented here. Theoretical calculations are based on a structural model built from our measured atomic parameters. The optical properties were measured by analyzing the diffuse reflectance data obtained with a Shimadzu UV-3101PC double-beam, double-monochromator spectrophotometer. This compound shows an absorption edge at about 360 nm corresponding to energy 3.44 eV. The theoretical calculations have been performed by using the full potential linearized augmented plane wave (FP-LAPW) method. We have used the generalized gradient approximation (GGA), using the exchange-correlation energy of Engel–Vosko. We present calculations of the frequency-dependent complex dielectric function ε(ω) and its zero-frequency limit ε1(0). The optical properties are analyzed and the origin of some of the spectral peaks is discussed in terms of the calculated electronic band energy structure. The linear optical properties show strong negative uniaxial anisotropy and birefringence which favors large second order susceptibility χ ijk ( 2 ) ( ω ) . Our calculations show that χ 333 ( 2 ) ( ω ) is the dominant component possessing the largest total Re χ ijk ( 2 ) ( 0 ) .