Linear and nonlinear optical susceptibilities and hyperpolarizability of borate LiNaB 4O 7 single crystals: Theory and experiment

Abstract

LiNaB 4O 7 was synthesized by employing high-temperature reaction methods. The purity of the sample was checked by x-ray powder diffraction. The optical properties were measured by analyzing the diffuse reflectance data which showed a band gap of about 3.88 eV. Linear and nonlinear optical susceptibility calculations have been performed using the all-electron full potential linearized augmented plane wave method using four different exchange correlation potentials. It was found that the title compound possesses an optical gap of about 2.80 eV using the local density approximation, 2.91 eV by generalized gradient approximation, 3.21 eV for the Engel-Vosko generalized gradient approximation (EVGGA), and 3.81 eV using modified Becke-Johnson potential (mBJ). This compares well with our experimentally measured energy band gap of 3.88 eV. Our calculations show that EVGGA and mBJ cause a blue spectral shift with significant changes in the whole spectra. The observed spectral shifts are in agreement with the calculated band structure and corresponding electron density of states. The tensor χ ijk (2) describes the second-order nonlinear optical effect and the symmetry allows only five nonzero components, namely, the 113, 232, 311, 322, and 333 components with 322 being the dominant one with a value 0.15 pm/V (d 32 0.0733 pm/V) at static limit and 0.16 pm/V (d 32 0.0795 pm/V) at λ 1064 nm. For the dominant component, the microscopic second order hyperpolarizability, β 322, was found to be 0.306 × 10 -30 esu at static limit and 0.332 × 10 -30 esu at λ 1064 nm.