Two haloid borate crystals with large nonlinear optical response

Abstract

The photophysical properties of the noncentrosymmetric haloid borates K₃B₆O₁₀X (X = Cl or Br) are calculated using density functional theory within the recently modified Becke–Johnson potential. The calculated electronic band structure reveals that the theoretical direct band gaps, 5.21 eV (K₃B₆O₁₀Cl) and 4.85 eV (K₃B₆O₁₀Br), are in good agreement with the previous calculation for K₃B₆O₁₀Cl (5.16 eV) and experimental data for K₃B₆O₁₀Br (4.86 eV). The calculated absorption coefficients, refractive indices, and birefringence are also in good agreement with the experimental data. The calculated nonzero second harmonic generation (SHG) coefficients, d₃₃, d₂₂ (= −d₂₁), and d₁₅(= d₃₂ = d₃₁), show good agreement with the experimental values. Furthermore, we have obtained the microscopic first hyperpolarizability for the dominant tensor component of the SHG.