Zhengdong Li

Ammonium nickel sulfate hexahydrate crystal: a new ultraviolet light filter

We propounded and grew a new crystal material of ammonium nickel sulfate hexahydrate (ANSH) for an ultraviolet light filter. The crystal structure of ANSH was solved by x-ray diffraction method and the empirical formula of the title compound is (NH4)2Ni(SO4)2⋅6H2O. The ANSH crystal belongs to the monoclinic space group P21/C, a = 6.2351 A, b = 12.451(3) A, c = 9.1798(18) A, β = 106.88(3)°, v = 681.9(2) A3, z = 2 and Dc = 1.924 g cm−3. The deep-green ANSH single crystal with a dimension of 20.5×28×15 mm3 has been grown by the cooling solution method. Thermo-gravimetry analysis showed that the dehydration temperature of the ANSH crystal is above 96.06°C, which is much higher than that of commercially available nickel sulfate hexahydrate (NSH) crystals. The optical transmission character of the ANSH crystal is discontinuous in the range from ultraviolet (UV) to near IR wavelengths, and has several transmission peaks at 250 nm, 500 nm, 875 nm and 1425 nm, respectively. The UV transmission peak (250 nm) especially has high transmission efficiency and a narrow spectrum band-width. The relationship between the structure and the optical transmission property is further discussed.

Nonlinear optical properties of some derivatives of stilbene and vinyl cyanide

Three derivatives of stilbene: 3-hydroxy-4-methoxy-4′-nitrostilbene (HMONS), 3-methoxy-4-hydroxy-4′-nitro-stilbene (MOHNS), 2-cyano-3-indole-propenoic acid ethyl ester (CIP-ethyl), and one derivative of vinyl cyanide: p-1,1-dicyano-vinyl-dimethylaminoaniline (DVDA) were designed and synthesized. The powder second-harmonic generation and absorption spectra of these four compounds were measured. First principle calculation of the molecular first hyperpolarizabilities of HMONS were calculated and compared with those of 3-methyl-4-methoxy-4′-nitrostilbene (MMONS, Appl. Phys. Lett. 56 (1990) 423) in order to elucidate their structural origin of the optical nonlinearity.

MBE growth and Raman studies of cubic and hexagonal GaN films on (001)-oriented GaAs substrates

Using different nucleation layers, we have grown cubic and hexagonal GaN epilayers on (001)-oriented GaAs substrates by radio-frequency plasma-assisted molecular beam epitaxy. First- and second-order Raman spectra are taken from these epilayers in back-scattering configurations at room temperature. For the first-order Raman spectra, transverse-optical (TO) phonons and longitudinal-optical (LO) phonons of cubic GaN are found to be at 533 and 739 cm(-1), as well as the E-2 and A(1)(LO) frequency of hexagonal GaN are found to be at 568 and 733 cm(-1), and the polarized spectra are in good agreement with Raman selection rules for cubic and hexagonal GaN, respectively. These results confirm the single crystalline nature of the samples. As for the second-order Raman spectra, the bands show a continuum, at about twice the energy of the LO phonon of cubic GaN and A(1)(LO) phonon of hexagonal GaN, which are nearly 10 times weaker than the first-order scattering. Two-phonon spectra are dominated by contributions due to longitudinal optical phonons

Growth of α-nickel sulphate hexahydrate for ultraviolet filters

Abstract Large clear crystals of α-nickel sulphate hexahydrate with dimensions of 65 × 85 × 75 (mm 3 ) have been grown by cooling an aqueous solution. The habit and condition of growth were observed. The grown crystals were optically characterized.

The study of ANSH crystallization from solution with concentration measurement by magnetic weigh method

Abstract A new design on solution density measurement described as the magnetic weigh method (MWM) is introduced. Inline solute concentration can be determined based on the definite relationship to the density of the solution. Several seed crystals have been used for crystallization in the study. The variances of excess saturation ratio S recorded by MWM show that seed crystals start to grow remarkably at S=0.13 and the crystallization rate is in proportion to S in spite of the crystal surfaces enlarged simultaneously. The ratio of linear and parabolic growth rates initially is analyzed to be approximately 3:2 and at low supersaturated concentration, the mechanism of the growth of crystal is deduced as diffusion and transport adsorption at the growing surface.

Large crystal growth and measurement of electro-optical coefficients of ADP ☆

Large crystals of ADP were grown from aqueous solution by temperature lowering method. The transmission spectrum curve, extinction ratio and optical homogeneity of the grown crystals were measured. The electro-optical coefficients were measured by the static method at wavelengths of 632.8 and 488.0 nm. The experimental results indicated that the crystals have good optical quality.