X.N. Jiang

Growth and properties of UV nonlinear optical crystal ZnCd(SCN)4

Abstract A second-order nonlinear optical coordination crystal, zinc cadmium thiocyanate, ZnCd(SCN) 4 (ZCTC) was grown as a frequency doubler, emitting UV light. A large typical single crystal with dimensions up to 15 × 7 × 7 mm 3 has been obtained by slow solvent-evaporation method for the first time. The infrared (IR) spectroscopy and X-ray powder diffraction (XRPD) of single crystals were performed at room temperature. The specific heat of the crystal has been measured to be 367.9 J/mol.K at 300 K. The thermal expansion coefficients, c- and a-oriented, have been measured to be −1.69 × 10 −5 and 1.95 × 10 −4 K −1 , respectively. The second harmonic generation (SHG) efficiency of ZCTC crystal is 51.6 times as high as that of urea reference, and the measured transmittance spectra from 190 to 3200 nm showed that the UV transparency cutoff occurs at 290 nm and the transmission is 73.22% at 380 nm. UV laser light of wavelength 380 nm has been achieved by the frequency doubling of a 760 nm laser diode at room temperature.

Growth of cadmium mercury thiocyanate dimethylsulphoxide single crystal for laser frequency doubling

This paper reports the growth of an organometallic nonlinear optical (NLO) complex crystal, Cadmium mercury thiocyanate dimethyl-sulphoxide (CdHg(SCN)4(H6CP2OS)2, CMTD), which was grown from aqueous solution by a temperature lowering method. Its powder SHG intensity is higher than that of CMTC. The crystal size of CMTD can reach 25×23×15mm3. The solubility curve, and solubility variation with pH value are also reported. The growth habits of crystals of CMTD grown under different conditions are discussed and the optimized condition for the growth CMTD using a temperature-lowering method from aqueous solution are also discussed.

Investigation of the Solution Structures and Determination of the Growth Units of Cadmium Mercury Thiocyanate Crystal

To get a better understanding of the growth of cadmium mercury thiocyanate (CMTC), a promising nonlinear optical crystal, we have investigated the structures of its growth solutions by using Raman spectra. It has been found that Hg(II) ions coordinate with SCN - through S atoms, forming the most stable complex of [Hg(SCN) 4 ] 2- in the solutions while Cd(II) ions bind to SCN around Hg(II) through the other end N atom. Thereby, taking [Hg(SCN) 4 ] 2- anions as centers, a network structure of Cd(II)-N-C-S-Hg(II) is formed in the solutions as in the crystal lattice. It is notably that there are other complexes, mostly the Cd(SCN) n (n<4) complexes, in the solutions. Therefore, the solution structure of CMTC is complicated, which is believed to contribute greatly to the difficulty of growing large single crystals. Based on the analysis of the solution structures, the reasonable growth units of CMTC are proposed.

Study on the micro-crystallization of cadmium mercury thiocyanate (CMTC) crystal for laser diode frequency doubling

Abstract The habit of cadmium mercury thiocyanate (CMTC) crystal for laser diode frequency doubling when crystallized from KCl–H2O solutions at 28°C under different conditions was investigated by means of a micro-crystallization method. The results show that CMTC crystals exhibit a regular crystalline morphology, homogenous growth rate in different directions and are transparent when the concentration of KCl ranges from 3% to 10% and pH from 3.0 to 4.0. Decrease in pH value leads to an increase in the crystallization rate along the c-axis direction, and a decrease along the a-axis direction. Impurities greatly affect the crystalline quality and morphology of the crystal. With aging and increasing temperature the solution becomes unstable. In this paper, suitable conditions and key factors for CMTC crystal growth are discussed.

Distinct Growth Phenomena Observed on Zinc Cadmium Thiocyanate Crystals by Atomic Force Microscopy

Atomic force microscopy is used to investigate the surface morphology of the prismatic (100) face of ZCTC crystal grown at 30°C at a supersaturation of 0.16. This surface is distinctly formed by periodic macrosteps that advance along different directions and join with each other leading to the interlaced growth layers with an inclination of about 137°. These two macrostep trains well correspond to the pyramidal faces of (011) and (011) in orientation, therefore they probably propagate from the edges of these faces. The macrosteps are practically formed by highly dense steps at the front with regular elementary steps in between. The alternation of macrosteps and elementary steps vividly reflects Chernovs kinematic waves of steps theory (CHERNOV, (1984)) on a nanometer scale. Wide indentations and long clefts are generated at the macrosteps. The former is generated by two-dimensional nucleation growth at a relatively faster growth rate than that of the underlying layer. The latter is probably caused by step trains generated by individual growth sources that have not merged.

Effect of excessive amount of Cd(II) cations on surface morphology of prismatic {1 1 0} faces of cadmium mercury thiocyanate crystals

Surface morphologies of cadmium mercury thiocyanate crystals grown from synthesized mother solutions with excessive amount of Cd(II) cations (5%, 20% and 50% in molar ratio) are investigated by atomic force microscopy. Unlike our previous observations, strong anisotropic growths occur at the large two-dimensional nuclei as well as at steps generated by 2D nuclei. These steps are highly bunched macrosteps varying from 1.6 up to 35 nm in height with distinctly well-oriented protuberance trains at the step fronts while regular elementary steps are hardly observed. These protuberances, however, become fewer and less distinct with the increase of excessive Cd(II) cations in the solution and even disappear at a much higher concentration of 50%. Steps also vary from macrosteps to dominant substeps with the height of 1 and 2 elementary steps of 0.81 nm at this high concentration. These distinct surface morphological variations are assumed to result from the effect of Cd–SCN complex anions as either growth units or impurities under different growth conditions. r 2002 Elsevier Science B.V. All rights reserved.

Direct Growth of Aggregates on {110} Faces of Cadmium Mercury Thiocyanate Crystals

New growth phenomena - direct incorporation of aggregates have been observed on the {110} faces of cadmium mercury thiocyanate CdHg(SCN) 4 crystals by atomic force microscopy. These aggregates grow in two forms: some directly cover up the steps and forms new growth layers; while others are just incorporated at the step edges. These aggregates, which are mostly oriented along [111] direction, are formed by small columnar structural units. The aggregates have the similar structure of CdHg(SCN) 4 crystals and greatly vary in nature with the variation of solution supersaturation σ and growth time t. With the increase of σ the aggregates become larger, consistent with the variation of growth units dimension with the supersaturation; and with the increase of growth time the aggregates become more structurally substantial. These observations have led to a new understanding about the crystal growth.

Atomic Force Microscopy Studies on Growth Mechanisms and Defect Formations on {110} Faces of Cadmium Mercury Thiocyanate Crystals

Growth mechanisms and defect formations on {110} faces of cadmium mercury thiocyanate crystals grown at 30°C (σ = 0.24)were investigated by using atomic force microscopy (AFM). It was found that, under this condition, spiral dislocation controlled mechanism and 2D nucleation mechanism operates simultaneously and equally during growth, which is completely different from the traditional 2D nucleation and dislocation source controlled mechanisms. A number of 2D nucleus are formed at the large step terraces generated by dislocation sources, leading to the unequal growth rates of the elementary steps and thereby step bunches are caused. Various defects are formed under this growth condition, which is assumed to result from the incongruence between the steps generated by different sources. A new kind of 2D defect, corresponding to one growth layer in height, was observed for the first time.