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Zinc sulphide is a chemical compound with white or yellow colour powder or crystal .It is typically encountered with a more stable cubic form, also known as zinc blende or sphalerite.
The hexagonal is also known as both a synthetic material and as mineral wurtzite.A tetragonal is also known as very rare mineral polhemusite (Zn,Hg)S. Both Sphalerite and wurtzite are intrinsic, wideband semiconductors. the cubic form has band gap of 3.54 eV at 300K whereas hexagonal has aband gap of 3.91 eV. The transition from the sphalerite form to wurtzite form occurs at around 1020 0 C .
The structure is a member of hexagonal crystal system and consists of tetrahedrally coordinated Zn and S atoms that are stacked in an ABABABAB.. pattern.
Unit cell parameters
ZN and S atoms are tetrahedrally coordinated. The structure is closely related to structure of diamond . It forms ABCABCABC.. Structure Lattice parameters a=0.541 nanometer
ZnS was used by Ernest Rutherford and others in the early years of nuclear physics as a scintillation detector, because it emits light on excitation by x-rays or electron beam, making it useful for x-ray screens and cathode ray tubes.
It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light.
Zinc sulfide, with addition of few ppm of suitable activator, is used as phosphor in many applications, from cathode ray tubes through x-ray screens to glow in the dark products. When silver is used as activator, the resulting color is bright blue, with maximum at 450 nm. Manganese yields an orange-red color at around 590 nm. Copper provides long glow time and the familiar glow-in-the-dark greenish color. Copper doped zinc sulfide (ZnS+Cu) is used also in electroluminescent panels.
Zinc sulfide is also used as an infrared optical material, transmitting from visible wavelengths to over 12 micrometres. It can be used planar as an optical window or shaped into a lens. It is made as microcrystalline sheets by the synthesis from hydrogen sulfide gas and zinc vapour and sold as FLIR (Forward Looking IR) grade ZnS a pale milky yellow visibly opaque form. This material when hot isostatically pressed (HIPed) can be converted to a water-clear form known as Cleartran (trademark). Early commercial forms were marketed as Irtran-2 but this designation is now obsolete.
It can be doped as both n-type semiconductor and p-type semiconductor, which is unusual for the II-VI semiconductors. ZnS is a covalently bonded solid.
Synthesis and photoluminescence characteristics of doped ZnS nanoparticles
Free-standing powders of doped ZnS nanoparticles
have been synthesized by using a chemical co-precipitation of Zn2+, Mn2+, Cu2+ and Cd2+ with sulphur ions in aqueous solution. X-ray diffraction analysis shows that the diameter of the particles is ∼ 2-3 nm. The unique luminescence properties,such as the strength (its intensity is about 12 times that of ZnS nanoparticles) and stability of the visible-light
Emission, were observed from ZnS nanoparticles co-doped with Cu2+ and Mn2+. The nanoparticles could be doped with copper and manganese during the synthesis without altering the X-ray diffraction pattern. However, doping shifts the luminescence
to 520-540 nm in the case of co-doping with
Cu2+ and Mn2+. .Doping also results in a blue shift on the excitation wavelength. In Cd2+-doped ZnS nanometer-scale particles, the fluorescence spectra show a red shift in the emission wavelength (ranging from 450 nm to 620 nm). Also a relatively broad emission (ranging from blue to yellow) has been observed. The results strongly suggest that doped
ZnS nanocrystals, especially two kinds of transition metal activated ZnS nanoparticles, form a new class of luminescent Materials.
Synthesis and photoluminescent properties of ZnS nanocrystals doped with copper and halogen
A wet-chemical precipitation method is optimized for the synthesis of ZnS nanocrystals doped with Cu+ and halogen. The nanoparticles were stabilized by capping with polyvinyl pyrrolidone (PVP). XRD studies show the phase singularity of ZnS particles having zinc-blende (cubic) structure. TEM as well as XRD line broadening indicate that the average crystallite size of undoped samples is ∼2 nm. The effects of change in stoichiometry and doping with Cu+ and halogen on the photoluminescence properties of ZnS nanophosphors have been investigated. Sulfur vacancy (VS) related emission with peak maximum at 434 nm has been dominant in undoped ZnS nanoparticles. Unlike in the case of microcrystalline ZnS phosphor, incorporation of halogens in nanoparticles did not result in Zn related self-activated emission. However, emission characteristics of nanophosphors have been changed with Cu+ activation due to energy transfer from vacancy centers to dopant centers. The use of halogen as co-activator helps to increase the solubility of Cu+ ions in ZnS lattice and also enhances the donor-acceptor type emission efficiency. With increase in Cu+ doping, Cu-Blue centers (CuZn−Cui+),which were dominant at low Cu+ concentrations, has been transformed into Cu-Green (CuZn−) centers and the later is found to be
situated near the surface regions of nanoparticles. From these studies we have shown that, by controlling the defect chemistry and suitable
doping, photoluminescence emission tunability over a wide wavelength range, i.e., from 434 to 514 nm, can be achieved in ZnS.
Simple synthesis of ZnS nanoparticles in alkaline medium
ZnS nanoparticles were successfully synthesized
by reflux under an alkaline medium. The
nanoparticles were characterized by using X-Ray diffraction(XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical properties of ZnS nanoparticles were examined by photoluminescence (PL) spectrum. The result shows that the assynthesized ZnS nanoparticles had a cubic phase. SEM image shows that ZnS nanoparticles are basically in spherical shape and are homogeneous. The particle size
was found to be in the range of 18 nm. All the reagents used in experiment were of analytical
purity and were used without further purification. An
appropriate amount of zinc chloride (0.1 M), sulphur
powder (0.1 M), NaOH (5 M) and deionised water
(100 mL) were refluxed together for 5 h under constant stirring. Upon reflux, the product was centrifuged and washed several times with deionised water. The sample was then dried in the oven at 80 0C for 2 h to obtain powders of ZnS nanoparticles which appear white in colour .The powders are highly stable and do not show any coalescence or agglomeration even after several months.
Preparation and photoluminescent properties of doped nanoparticles of ZnS by solid-state reaction
Nanometer-sized Eu3+ -doped ZnS and Mn2+-doped ZnS particles were prepared bysolid-state method at low temperature.The structures and properties of those materials were characterized by X-ray diffraction (XRD) and photoluminescent spectroscopy techniques. The XRD patterns reveal that the doped ZnS nanoparticles belong to zinc-blende structure .The concentration of doping ions has little effect on the sizes of the doped ZnS nanoparticles ,which mainly depends on the temperature of preparation. The emission peaks from the 5D0-7FJ (J ¼ 1,2,and4) electronic energy transitions of Eu3+ were observed in the emission spectra of theZnS:Eu3+ nanoparticles .The intensity ratio of the two peak sfrom the 5D0-7F1 and 5D0-7F2 transitions indicates that more Eu3+ ions occupy the sites with no inversion symmetry . For the ZnS:Mn2+ nanoparticles , an orange emission from the 4T1-6A1 transition of Mn2+ is present ,indicating that the doping ions occupy the positions of the ZnS lattices . Meanwhile, UV-induced luminescence enhancement was observed for the ZnS:Mn2+ nanoparticles , the possible reason of which is discussed primarily.
A new preparation of zinc sulphide nanoparticles by solid state method at low temperature.
A novel solid-state method of the preparation of zinc sulphide nanoparticles is reported. By solid-state reaction of zinc acetate and thioacetamide at low temperature, zinc sulphide nanoparticles of different sizes were prepared. The temperature of preparation varied from room temperature to 300°C. The particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and photoluminescence spectrum. X-ray diffraction patterns revealed that the particles exhibited pure zinc-blende crystal structure and that particle size increased with increasing temperature. The TEM micrograph showed that the mean particle size was about 40 nm for the sample heated at 100°C. A blue shift was observed in the photoluminescence emission spectrum. A possible mechanism of the reaction corresponding to our observation is proposed.