Guiwu Lu

A systematic spectroscopic study of four bimetallic thiocyanates of chemical formula AB(SCN)4: ZnCd(SCN)4 and AHg(SCN)4 (A=Zn, Cd, Mn) as UV nonlinear optical crystal materials

Abstract Bimetallic thiocyanate complexes of chemical formula AB(SCN)4(ABTC): ZnCd(SCN)4 and MHg(SCN)4 (M=Zn, Cd, Mn) were discovered as potentially useful crystal materials in ultraviolet second-harmonic generation. The structures of these compounds were derived from powder X-ray diffraction data, and unit-cell parameters were calculated by the TREOR program. Their vibrational spectra were studied by Raman spectroscopy, which show that the characteristic vibrational modes of AB(SCN)4 crystals arise mainly from the internal vibrations of the SCN, A(NCS)4, and B(SCN)4 clusters. The reason of the high optical nonlinearities of ABTC crystals has been studied by the use of the Raman spectra and the molecular orbital theory: the distorted A(NCS)4 and B(SCN)4 tetrahedra and the conjugated charge-transfer (–A–NCS–B–) bridges that connect all the distorted tetrahedra together.

Lattice vibration and absorbance of Er:Yb:YCOB single crystals

Abstract Er 3+ - and Yb 3+ -doped yttrium calcium oxoborate Er:Yb:YCa 4 O(BO 3 ) 3 (Er:Yb:YCOB) crystallizes with a fluorapatite-type structure in the monoclinic system. Its lattice vibrational modes were calculated by using space group theory, and Raman spectra were measured at room temperature with different scattering geometry projects. The experiments show that the characteristic lattice vibrational modes of Er:Yb:YCOB crystal arise mainly from the internal vibrations of the BO 3 , CaO 6 , and YO 6 groups. The three-dimensional network structure of Er:Yb:YCOB crystal is identified, and its excellent nonlinear optical (NLO) properties are mainly attributed to the BO 3 clusters that connects all the distorted YO 6 and CaO 6 octahedral clusters together. The combination of the strong absorption at 976 nm and the strong emission at 1537 nm makes this material very promising for use in an infrared laser system.

Vibrational spectra and theoretical study of ZnCd(SCN)4 single crystal

Abstract The vibrational spectra of the zinc cadmium thiocyanate (ZCTC) single crystal are studied by Raman spectroscopy and ab initio calculation with the molecular orbital (MO) theory using a G aussian 98 program. Agreement is achieved between the vibrational wavenumbers predicted by the theory and those observed in Raman scattering experiments. The results show that the characteristic vibrational modes of ZCTC crystal arise mainly from the internal vibrations of the SCN, Zn(NCS)4, and Cd(SCN)4 clusters. The three-dimensional network structure of ZCTC crystal is identified, and the high optical nonlinearity of the crystal is chiefly ascribed to the conjugated charge-transfer (–Zn–NCS–Cd–) bridges that connect all the distorted Zn(NCS)4 and Cd(SCN)4 tetrahedra together.

A Monte Carlo simulation on structure and thermodynamics of potassium nitrate electrolyte solution

Monte Carlo computer simulation of potassium nitrate solution is carried out in the concentration ranging from 0.3 to 7.0 mol l−1. The cation (K+) and solvent water molecules are regarded as the charged and dipolar hard sphere respectively, and a simple four-site model for the nitrate ion is adopted in this study. It is found that there is an abrupt decline in the pressure with increasing ion concentration at fixed temperature. In supersaturated solutions for temperatures of 303 and 333 K, a metastable state with negative pressures and a strong energy fluctuation are observed. Some large ionic clusters are observed in supersaturated solutions at a temperature of 333 K, and they are composed of an ionic chain with alternating sign which indicates the formation of crystallization morphology. With decreasing solution concentration, the ionic hydration number varies from 5–7 for cation K+ and 3.5–4.7 for anion NO , which is in good agreement with time-of-flight neutron diffraction results.