Xuean Chen

Linear and nonlinear optical susceptibilities and the hyperpolarizability of borate LiBaB9O15 single-crystal: theory and experiment.

The single-crystal borate LiBaB9O15 was synthesized by a high-temperature solution reaction and structurally determined by the single-crystal X-ray diffraction technique. It crystallizes in the noncentrosymmetric space group R3c and features a three-dimensional ∞3[B9O15]3– anionic framework, with infinite channels in which the Li+ and Ba2+ cations are located. The linear optical properties were investigated experimentally in terms of the absorption spectrum, which reveals an optical gap of 5.17 eV. In addition we have calculated the linear optical properties using state-of-the-art all-electron full potential linearized augmented plane wave method. The nonlinear optical susceptibilities, namely, the second harmonic generation and the hyperpolarizability of the single-crystal borate LiBaB9O15 are calculated and evaluated at a static limit and at λ = 1064 nm. The calculation shows there exists three second-order nonlinear optical susceptiblities tensors components. We present measurements of the IR spectra in the range 500–2000 cm–1, and the second harmonic generation was performed using a Quantel 15 ns Nd:YAG laser operating at 1064 nm.

X-ray diffraction and optical properties of a noncentrosymmetric borate CaBiGaB2O7

Single crystals of the noncentrosymmetric borate CaBiGaB(2)O(7) were synthesized by conventional solid state reaction. The purity of the crystal was checked by x-ray powder diffraction. The optical properties were measured by analyzing the diffuse reflectance data obtained with a Shimadzu UV-3101PC double-beam, double-monochromator spectrophotometer. We find a steep absorption edge confirming its semiconducting nature. The optical band gap obtained by extrapolation of a linearlike absorption edge was roughly 2.9 eV consistent with the observed pale yellow color of the sample. Theoretical calculations based on the structural model built from our measured atomic parameters have been performed using the all-electron full potential linearized augmented plane wave method. The generalized gradient approximation (GGA) of the exchange correlation potential as given by Engel-Vosko GGA is used. The frequency-dependent complex dielectric function was calculated and the origin of some of the spectral peaks is discussed. The linear optical properties show strong uniaxial anisotropy and birefringence that favors large second order susceptibility. Our calculations show that the complex second order nonlinear optical susceptibility tensor chi(322) ((2))(omega) is the dominant component having the largest total Re chi(322) ((2))(0) value of about 1.8 pm/V.

Linear and nonlinear optical susceptibilities and hyperpolarizability of borate LiNaB4O7 single crystals: Theory and experiment

LiNaB4O7 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 calcul...

X-ray Diffraction, X-ray Photoelectron Spectra, Crystal Structure, and Optical Properties of Centrosymmetric Strontium Borate Sr2B16O26

We report results of X-ray diffraction (XRD) and valence band X- ray photoelectron (VB-XPS) spectra for strontium borate Sr(2)B(16)O(26). The X-ray structural analysis shows that the single crystals of Sr(2)B(16)O(26) crystallize in the monoclinic space group P2(1)/c with a = 8.408(1) A, b = 16.672(1) A, c = 13.901(2) A, beta = 106.33(1) degrees , and Z = 4. The crystal structure consists of a 3D network of the complex borate anion [B(16)O(20)O(12/2)](4-), formed by 12 BO(3) triangles and four BO(4) tetrahedra, which can be viewed as three linked [B(3)O(3)O(4/2)](-) triborate groups bonded to one pentaborate [B(5)O(6)O(4/2)](-) group and two BO(3) triangles. Using this structure, we have performed theoretical calculations using the all-electron full potential linearized augmented plane wave (FP-LAPW) method for the band structure, density of states, electron charge density, and the frequency-dependent optical properties. Our experimental VB-XPS of Sr(2)B(16)O(26) is compared with results of our FP-LAPW calculations. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Gamma of the Brillouin zone (BZ) resulting in a direct energy gap of about 5.31 eV. Our measured VB-XPS show reasonable agreement with our calculated total density of states for the valence band that is attributed to the use of the full potential method.

X-ray diffraction, crystal structure, and spectral features of the optical susceptibilities of single crystals of the ternary borate oxide lead bismuth tetraoxide, PbBiBO4.

The all-electron full-potential linearized augmented plane-wave method has been used for an ab initio theoretical study of the band structure, the spectral features of the optical susceptibilities, the density of states, and the electron charge density for PbBiBO4. Our calculations show that the valence-band maximum (VBM) and conduction-band minimum (CBM) are located at the center of the Brillouin zone, resulting in a direct energy gap of about 3.2 eV. We have synthesized the PbBiBO4 crystal by employing a conventional solid-state reaction method. The theoretical calculations in this work are based on the structure built from our measured atomic parameters. We should emphasize that the observed experimental X-ray diffraction (XRD) pattern is in good agreement with the theoretical one, confirming that our structural model is valid. Our calculated bond lengths show excellent agreement with the experimental data. This agreement is attributed to our use of full-potential calculations. The spectral features of the optical susceptibilities show a small positive uniaxial anisotropy.