Alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr3Be3B3O9F4 with large nonlinear optical properties in the deep-ultraviolet region

摘要

The linear optical response and second harmonic generation (SHG) in alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr3Be3B3O9F4 are investigated by means of density functional theory. Calculations are performed using four types of exchange correlations: Ceperley-Alder local density approximation, Perdew Burke and Ernzerhof general gradient approximation, Engel-Vosko generalized gradient approximation, and the recently modified Becke-Johnson potential (mBJ). The mBJ approach brings the calculated band gap (7.20 eV) in excellent agreement with the experimental one (7.28 eV). The calculated values of the uniaxial anisotropy delta epsilon = -076 and the birefringence Delta n(0) = 052 indicate considerable anisotropy in the linear optical properties, which makes it favorable for the second harmonic generation. The dominant component of the second harmonic generation is chi((2))(111)(omega). The value of vertical bar chi((2))(111)(omega)vertical bar is about 1.2 pm/V at lambda = 1064 nm in agreement with previous calculations. To analyze the origin of the high SHG of NaSr3Be3B3O9F4 single crystals, we have correlated the features of vertical bar chi((2))(111)(omega)vertical bar spectra with the features of epsilon(2)(omega) spectra as a function of omega/2 and omega. From the calculated dominant component vertical bar chi((2))(111)(omega)vertical bar, we find that the microscopic first hyperpolarizability, beta(111), the vector components along the dipole moment direction is 0.5 x 10(-30) esu at static limit and 0.6 x 10(-30) esu at lambda = 1064 nm. ud