Investigation on one-pot hydrothermal synthesis, structural and optical properties of ZnS quantum dots

The advantage of hydrothermal synthesis of semiconductor quantum dots (QDs) over the control of particles size, morphology and stability is reported here. In a typical synthesis procedure, the zinc and sulfur precursor molar ratio of 1:3 was used in an aqueous solution at 150 degrees C. The cubic phase of ZnS with average particles size of 5 nm was confirmed and estimated from the X-ray diffraction (XRD) analysis. The composition and purity of the sample were analyzed from (energy dispersive-ray analysis) EDAX and (X-ray photoelectron spectroscopy analysis) XPS spectra. The absorption spectrum shows the large shift in the absorption band over 90 nm due to the quantum confinement of carriers. The emission spectrum of quantum dots carry more evidence on the presence of shallow trap, deep trap in the band gap of the material responsible for weak emission in the spectral region of 450-500 nm. High resolution transmission electron microscope and scanning electron microscope studies reveal the structural and morphological features of ZnS with slightly distorted spherical morphology. We found that the coordinating ability of solvent strongly influences the reaction process and morphology of the products

Synthesis and Physicochemical Investigation of THz Material: 4–Ethoxy Benzaldehyde–4'–N'–Methyl Stilbazolium Hexafluorophosphate (EMBSHP)

International audienceSingle crystals of organic optic material 4–Ethoxy Benzaldehyde–4'–N'–Methyl Stilbazolium Hexafluorophosphate (EMBSHP) were grown by slow evaporation technique at room temperature using acetone – water (3:1) mixed solvent. The grown crystal was subjected to single crystal X – ray diffraction analysis to identify the crystal structure and lattice parameter. The crystal belongs to the triclinic crystal system. The composition of the crystal was studied by CHN analysis. The presence of functional groups of the title crystal were confirmed from the FTIR spectral studies. The optical transmission range of the grown crystal was measured by UV – Vis – NIR spectral studies. The melting point of the grown crystal was found from DSC analysis. Introduction. Organic NLO materials with excellent optical characteristics such as high sensitivity and short response time have attracted much attention due to their potential applications in optical switching, optical processing, optical computing, optical data storage and terahertz (THZ) technology. Among the numerous organic materials, the well-known and most investigated organic NLO crystal is the stilbazolium salt trans-4-N-(dimethylamino)-N-Methyl-4-stilbazolium tosylate (DAST). It has very high electro optical (EO) and NLO figures of merit. Among all the other organic THz material, DAST has the largest NLO coefficient, d11 of 540 ± 110 pm/V at ~1540 nm, EO figure of merit r11=47 ± 8 pm/V at ~1535 nm and lower dielectric constant making it suitable for optoelectronic applications [1,2]. The advancement in the field of photonics have increased the demand for new nonlinear optical (NLO) materials. Especially, molecules exhibiting strong two photon absorption (TPA) are of practical importance in photons applications such as frequency up conversion lasing, three dimensional fluorescence imaging and multi photon microscopy ,eye and sensor protection, optical signal reshaping and stabilizing fast fluctuations of laser power. To expand these utilizing, designing the molecule with large TPA cross section plays a vital role [3]. DAST crystal can generate short THz pulse by optical rectification with a sub-picosecond laser [4, 5], or widely tunable THz waves by different frequency generation (DFG) with a dual wavelength nanosecond laser [6]. In this present study, the tosylate anion of DAST is replaced by Hexafluorophosphate (PF-6) and two methyl group along with nitrogen in the cation is replaced by ethoxy group for achieving the stilbazolium crystal 4-Ethoxy benzaldehyde 4'-N'-methyl stilbazolium Hexafluorophosphate (EMBSHP). The grown crystal has been subjected to single crystal XRD, CHN, FTIR, Optical absorption and thermal analysis