Two haloid borate crystals with large nonlinear optical response

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, d(33), d(22) (= -d(21)), and d(15)(= d(32) = d(31)), show good agreement with the experimental values. Furthermore, we have obtained the microscopic first hyperpolarizability for the dominant tensor component of the SHG.