ZnS Crystals Research Articles

The Study of Near-Band-Edge Property in Oxygen-Incorporated ZnS for Acting as an Efficient Crystal Photocatalyst.

A wide gap semiconductor material has attracted attention as a heterophotocatalyst because of its light harvesting nature to be used in alternative energy production for the next generation. We, herein, grow and synthesize ZnS(1–x)Ox series compounds using the chemical vapor transport (CVT) method with I2 serving as the transport agent. Different crystals, such as undoped ZnS and oxygen-doped ZnS0.94O0.06 and ZnS0.88O0.12, revealed different bright palette emissions that were presented in photoluminescence spectra in our previous report. To study the electron–hole pair interaction of this sample series, the near-band-edge transitions of the sample series were characterized in detail by photoconductivity (PC) experiments. Additional results from surface photovoltage (SPV) spectra also detected the surface and defect-edge transitions from the higher oxygen-doped ZnS crystals. PC measurement results showed a red-shift in the bandgap with increasing incorporation of oxygen on ZnS. Consequently, the samples were subjected to photoirradiation by xenon lamp for the degradation of methylene blue (MNB) by acting as heterophotocatalysts. Undoped ZnS emerged as the best photocatalyst candidate with the fastest rate constant value of 0.0277 min–1. In cubic {111} ZnS [{111} c-ZnS], the polarized Zn+ → S– ions may play a vital role as a photocatalyst because of their strong electron–hole polarization, which leads to the mechanism for degradation of the MNB solution.

Investigation of channeling and radiation of relativistic electrons in charged planes of the crystals with zinc blende structure

In this paper the interaction potentials of relativistic electrons with the charged (2m+1, 2n+1, 2p+1) and (2m+1, 2n, 2p) planes (m, n, p=0,1,ṡ, and Miller indices are mutually prime numbers) in the crystals with a zinc blende structure are calculated using Moliere approximation. It is shown that at the change of the type of used crystal plane (from the main (100) to the high-index charged planes), the structures of potential wells are transformed from non-unimodal to unimodal ones. In this case for the crystals constructed from ions with close nucleus charges, there arise so-called positron-like potential wells for the channeled electrons, i.e. with minima in the interplanar space. The influence of temperature factor on interaction potentials structures is also investigated. For the electrons with Lorentz-factors γ = 25, 50, 75 in the main (100) and (111) planes the transverse energy levels and corresponding wave functions in single planar approximation are found numerically. By means of these data the spectra of channeling radiation (CR) in dipole approximation are calculated for the electrons beams with a Lorentz-factor γ = 50 and an angular dispersion θ 0 ≈ 0,5 mrad, arising in the main charged (100) and (111) planes in ZnS, ZnSe and ZnTe crystals. It is shown that the CR generated at electron channeling along the (111) planes is more intense. It is shown also that spectra of CR arising in (111) planes of silicon and AlP crystals at using of channeled electron beam with γ = 25 and an angular dispersion θ 0 ≈ 0,5 mrad, due to similarity of structures of potential wells are identical. The spectra of CR at γ = 25, 50, 75 are calculated for a number of crystals with a zinc blende structure, namely AlP, AlAs, AlSb, GaP, GaAs, InP, InAs, InSb.

Optical Study of High Quality c -ZnS Crystals for UV Photodiodes and Photoelectrochemical Applications

Wide band gap semiconductors are proper candidates for manufacturing UV-visible electronic devices, photocatalysts and power electronic components. Among them, II–VI ZnS has a high flexibility in tuning energy range as compared to ZnO because of a larger bandgap about 3.7 eV. In this work, a high-quality {111}-oriented ZnS crystal of zinc-blende structure has been successfully grown by chemical vapor transport method using I2 as the transport agent. High-resolution transmission electron microscopy verifies its crystallinity and crystal orientation, and energy dispersive X-ray analysis identifies its stoichiometry. Due to the coupling between crystal field and spin orbital in the high quality solid, three band-edge excitonic transitions of EA=3.745, EB=3.799 and EC=3.881 eV have been detected. An initial metal-semiconductor-metal (MSM) Schottky photodiode made by {111}-ZnS crystal has been assessed. The dark resistivity is about 6.13 MΩ-cm. Under the irradiation of a 266-nm laser (power ∼1.6 mW), the photo-resistivity change (i. e., Δρ/ρdark) reaches 88%. Photo-catalytic ability of the {111}-ZnS single crystal was also evaluated using Methyl-blue degradation. The degradation (normalized concentration change) after 1 hour can reach C/C0≈ 0.47 under irradiation of Xe-arc lamp. All the experimental results reveal high responsivity of the {111}-ZnS photodiode and good photocatalytic function of the {111}-oriented crystal photocatalyst operated in the UV range.

Formation of dislocation loops and voids in electron irradiated zinc selenide single crystals

The formation of small dislocation loops in size of 2.5 - 45 nm and a density of 1.4·1011 cm−2, as well as voids in size ≤10 nm in ZnS crystals were found by the transmission electron microscopy method (TEM). Samples were examined and irradiated in situ in a JEOL 4000EX-II electron microscope operated at energy of 400 keV and intensity of (1 - 4)·1019 e/cm2·s. Fine particles of a new phase in size ≤10 nm are formed also. These features can be identified from an analysis of moiré fringe contrast as phase of ZnO2. Similar defects in single crystals of ZnS formed in situ after irradiation in a transmission electron microscope JEM-100CX operated at energy of 100 keV and intensity of 3,5·1017 e/cm2·s. It was found that the formation of structural defects in ZnS under electron irradiation with above-threshold energy of defect formation (400 keV) is similar to the formation of structural defects in these crystals under electron irradiation with sub-threshold defect formation energy (100 keV).

Synthesis and Optical Characterization of Oxygen-Incorporated ZnS(1-x)O x for UV-Visible Color Palette Light-Emission Matter.

Single crystals of oxygen-incorporated ZnS (i.e., ZnS(1–x)Ox series) are environment-friendly wide-band-gap semiconductors available for light-emitting devices and solar cell use. The series of materials has considerable potential for use in visible ultraviolet areas with flexibility for palette emissions. In this study, we grow oxygen-incorporated ZnS series crystals by chemical vapor transport method with iodine (I2) as the transport agent. Three different oxygen-incorporated crystals of undoped ZnS, ZnS0.94O0.06, and ZnS0.88O0.12 are studied. Through structural studies, ZnS doped with oxygen crystallizes in the main sphalerite phase and a little wurtzite structure. The lattice constants of the major cubic phase are determined to be a = 5.43 Å (ZnS), 5.41 Å (ZnS0.94O0.06), and 5.39 Å (ZnS0.88O0.12). Three band-edge excitonic transitions are simultaneously detected by thermoreflectance measurement for the ZnS, ZnS0.94O0.06, and ZnS0.88O0.12 series samples. The energy positions of the band-edge transitions decrease as the oxygen content increases in the ZnS(1–x)Ox series. Defect-state and surface-state emissions, including sulfur vacancy, oxygen vacancy, zinc interstitial, and so forth, can emit approximately full-color spectra from the near band edge of the ZnS(1–x)Ox series crystals. With adjusting the oxygen content, the ZnS(1–x)Ox can be a series of color-palette luminescence matters that applied for fluorescent display or light-emitting device.

Low-temperature surface preparation and epitaxial growth of ZnS and Cu2ZnSnS4 on ZnS(1 1 0) and GaP(1 0 0)

We give a summary of the low-temperature preparation methods of ZnS(110) and GaP(100) crystals for epitaxial growth of ZnS and Cu2ZnSnS4 (CZTS) via molecular beam epitaxy. Substrates were prepared for epitaxial growth by means of room-temperature aqueous surface treatments and subsequent ultra-high vacuum transfer to the deposition system. Epitaxial growth of ZnS was successful at 500K on both ZnS(110) and GaP(100) as only single domains were observed with electron backscatter diffraction; furthermore, transmission electron microscopy measurements confirmed an epitaxial interface. Epitaxial growth of CZTS was successful on ZnS at 700K. However, epitaxial growth was not possible on GaP at 700K due to GaxSy formation, which significantly degraded the quality of the GaP crystal surface. Although CZTS was grown epitaxially on ZnS, growth of multiple crystallographic domains remains a problem that could inherently limit the viability of epitaxial CZTS for model system studies.

The Optical Nonlinearities of Zinc Semiconductor Crystals under Different Laser Pulse Width

Based on Z-scan technique, the nonlinear absorption characteristics and nonlinear refraction characteristics of ZnO crystal, ZnS crystal and ZnSe crystal were studied under the picosecond (ps) laser pulses and the femtosecond (fs) laser pulses respectively. The experimental results show that the nonlinear absorption characteristics of the three kinds of crystals are reverse saturable absorption mainly due to two-photon absorption under the ps laser pulses. The nonlinear refraction characteristics are self-defocusing and the nonlinear refractive indexes are positive because of free carrier. The nonlinear absorption characteristics of the ZnO crystal and ZnS crystal are reverse saturable absorption mainly due to three-photon absorption under the fs laser pulses, and the ZnSe crystal is two-photon absorption. The nonlinear refraction characteristics of the three kinds of crystals are self-focusing because of bound electron. The experimental results show that zinc semiconductor crystals materials and laser pulse width can influence the optical nonlinear characteristics of materials.

Mechanism study on the sulfidation of ZnO with sulfur and iron oxide at high temperature

The mechanism of ZnO sulfidation with sulfur and iron oxide at high temperatures was studied. The thermodynamic analysis, sulfidation behavior of zinc, phase transformations, morphology changes, and surface properties were investigated by HSC 5.0 combined with FactSage 7.0, ICP, XRD, optical microscopy coupled with SEM-EDS, and XPS. The results indicate that increasing temperature and adding iron oxide can not only improve the sulfidation of ZnO but also promote the formation and growth of ZnS crystals. Fe2O3 captured the sulfur in the initial sulfidation process as iron sulfides, which then acted as the sulfurizing agent in the late period, thus reducing sulfur escape at high temperatures. The addition of carbon can not only enhance the sulfidation but increase sulfur utilization rate and eliminate the generation of SO2. The surfaces of marmatite and synthetic zinc sulfides contain high oxygen due to oxidation and oxygen adsorption. Hydroxyl easily absorbs on the surface of iron-bearing zinc sulfide (Zn1−xFexS). The oxidation of synthetic Zn1−xFexS is easier than marmatite in air.

Synthesis of core-shell-like ZnS/C nanocomposite as improved anode material for lithium ion batteries

ZnS/C nanoparticles with core/shell structure are prepared by a simple solvothermal process followed by an annealing process. The core consists of a quite amount of ultrasmall ZnS nanocrystals (∼10nm) dispersing in in situ formed carbon matrix, which is covered by an outer carbon shell with ∼4nm thickness. The nano-sized ZnS crystals effectively shorten the lithium ion diffusion paths, while the uniform carbon shell, together with the inner amorphous carbon matrix not only provide fast electron conduction, but also act as a buffer matrix to accommodate volume change occurring on electrochemical cycling. Such hierarchical-type microstructure is beneficial concerning electrochemical performance of the proposed composite. When evaluated as an anode material for rechargeable lithium ion batteries, the ZnS/C nanocomposite shows a high specific capacity of 741mAhg−1 at a current density of 0.1Ag−1 after 300 cycles. Even at 5Ag−1, a high reversible capacity of 538mAhg−1 can be still achieved. The lithium diffusion coefficient of ZnS/C electrode is estimated as 6.1×10−11cm2s−1, contributing to the excellent rate performance of the material.

Kerr-lens mode-locked polycrystalline Cr:ZnS femtosecond laser pumped by a monolithic Er:YAG laser**Project supported by the National Natural Science Foundation of China (Grant Nos. 61205130, 61465012, and 61564008).

We demonstrated a Kerr-lens mode-locked polycrystalline Cr:ZnS laser pumped by a narrow-linewidth linear-polarised monolithic Er:YAG nonplanar ring oscillator operated at 1645 nm. With a 5-mm-thick sapphire plate for intracavity dispersion compensation, a compact and stable Kerr-lens mode-locking operation was realised. The oscillator delivered 125-fs pulses at 2347 nm with an average power of 80 mW. Owing to the special polycrystalline structure of the Cr:ZnS crystal, the second to fourth harmonic generation was observed by random quasi-phase-matching.

Electron microscopy study of the structural defect formation in ZnS under irradiation by electrons with energy of 400 keV

ZnS crystals grown form the vapor phase and ZnS/(001)GaAs epitaxial structures grown by metalorganic vapor phase epitaxy are studied by transmission electron microscopy after in situ irradiation in an electron microscope at an electron energy of 400 keV and intensity of (1–4) × 1019 electrons/cm2 s. It is shown that irradiation leads to the formation of small (2.5–45 nm) dislocation loops with a density of 1.4 × 1011 cm–2, as well as voids and new phase inclusions ≤10 nm in size. Using the moire fringe contrast analysis, these inclusions were identified as ZnO and ZnO2.

Weak d0 ferromagnetism: Zn vacancy condensation in ZnS nanocrystals

We provide the explanation of the large discrepancy of three orders of magnitude between the experimentally measured and theoretically calculated magnetic moments in ZnS nanocrystals. We assume that the condensation of Zn vacancies into a single droplet takes place. The energy calculations reveal that the droplet phase is more favorable than the uniformly distributed vacancy configuration. The other assumption made is that a small magnetic moment could arise at the interface between the ZnS crystal and vacancy cluster. The calculations however dismiss this hypothesis because the magnetization of the layered system also vanishes. Thus we suggest that the experimentally low magnetization values could be explained from one of the two following pictures: (a) there are two phases where the vacancy cluster with the zero magnetic moment coexists along with the other phase, in which there are uniformly distributed Zn vacancies with low concentrations or (b) there is only a single vacancy phase—a vacancy droplet being in the metastable state with a weak nonvanishing magnetic moment.

Growth of high optical quality zinc chalcogenides single crystals doped by Fe and Cr by the solid phase recrystallization technique at barothermal treatment

The method of growing of ZnS and ZnSe single crystals doped with chromium and iron using a combination of the solid phase recrystallization and diffusion doping during the high-temperature gas-static pressing has been implemented. The isostatic pressing up to 110MPa has made it possible to increase the process temperature up to 1300°C, increase the rate of grain growth and diffusion of Fe2+ and Cr2+ ions in zinc chalcogenides crystalline samples, reduce processing time to 25–150h. ZnS:Cr (Fe) and ZnSe:Cr (Fe) single crystals from several to tens mm in size with dopant concentrations of (1–5)×1019cm−3 for Cr2+ and (5–20)×1018cm−3 for Fe2+ and at the total impurity's content no more than 5×10−4wt% have been obtained. The lasers made from the crystals demonstrated 55% differential lasing efficiency for the absorbed power.

Site spectroscopy of Eu3+ doped- ZnS nanocrystals embedded in sodium carboxymethyl cellulose matrix

The work investigates the incorporation of Eu3+ ion in ZnS crystal through spectroscopic studies. ZnS: Eu3+ nanocrystals was synthesized via the precipitation technique. Elemental composition analysis indicates a non-stoichiometric distribution between Zn and S. X-ray diffraction studies show lattice expansion demonstrating that Eu3+ ions were incorporated in the host lattice. Annealing temperature gave rise to lattice contraction relative to the as-synthesized indicating a partial expulsion of the ion from the crystal due to heat treatment. Eu3+ ions site symmetry probing from optical features show that trivalent europium were situated both at the nanocrystals surface and at the Zn2+ ion site. Weak energy transfer from host to activator ion occurred probably mainly through exchange interaction and the transfer process was defect mediated.

Graded ZnS/ZnSxO1−x heterostructures produced by oxidative photolysis of zinc sulfide: Structure, optical properties and photocatalytic evolution of molecular hydrogen

Abstract The photolysis of microcrystalline and single crystal ZnS on the ambient air was found to result in the formation of metallic zinc clusters and radical sulfur species additionally to the elimination of sulfur in reactions with oxygen and generation of S vacancies. The latter process results in the formation of a graded alloyed ZnO x S 1−x layer with a continuously decreasing content of sulfur and increasing content of oxygen from the bulk to the surface of the crystals. These photolytic changes are observed within the surface layer with a thickness of 50–80 nm which is comparable to the depth of light penetration into the ZnS crystals. Coupling of ZnS to ZnO, both via pre-photolysis thermal oxidation of ZnS in the dark or by in situ formation of ZnO via the oxidative photocorrosion of ZnS accelerates the photolysis considerably, most probably, as a result of directed and opposite flow of the electrons and holes within the graded ZnO x S 1−x layer and suppression of the electron-hole recombination. The ZnS/ZnS x O 1−x heterostructures revealed a relatively high photocatalytic activity in hydrogen evolution from water/ethanol mixtures under illumination with the UV light with a quantum yield of up to 1.6% in the absence of any co-catalysts. The dependence between the rate of photocatalytic hydrogen formation and the duration of ZnS photolysis was found to be dome-shaped one as a result of the interplay of two factors—(i) an increase of the probability of the spatial separation of the electron and hole within the ZnO x S 1−x layer and (ii) a decrease of the probability of ethanol oxidation by the holes with an increase in the ZnS x O 1−x layer thickness (or photolysis duration as an equivalent). In the optimal conditions the rate of photocatalytic H 2 evolution was 30 times higher than that for original non-photolyzed ZnS owing to the unique graded structure of the alloyed zinc oxysulfide layer produced by the oxidative photolysis.

Growth of high optical quality zinc chalcogenides single crystals by solid phase recrystallization technique at barothermal treatment

The solid phase recrystallization (SPR) technique under a barothermal high-temperature gas-static pressing (HIP) treatment was implemented to the growth for ZnS and ZnSe single crystals. The application of 200MPa isostatic pressure allowed increasing the process temperature up to 1150–1300°C, which in turn has increased the rate of grain growth and reduced process duration to 8–52h. The impurity contents in ZnS and ZnSe single crystals did not exceed 10−4wt%. The obtained crystals demonstrated transmittance in the wide VIS-IR spectral range close to the theoretical, ranging in size from a few to tens mm, which allows their use in practical applications as a laser matrix.

Theoretical Studies on the Intrinsic Defects in ZnO and ZnS Crystal

Theoretical Studies on the Intrinsic Defects in ZnO and ZnS Crystal

The structural defects formation in ZnS under electron irradiation with energy 400 KeV

The formation of structural defects in grown from the vapour phase ZnS crystals after electron irradiation with energy of 400 keV and intensity of 1 - 4.1019 e/cm2.s in situ in electron microscope was studied. It is shown that under electron irradiation the small dislocation loops in size of 2.5 - 45 nm and a density of 1.4-1011 cm-2, as well as voids and fine particles of a new phase in size ≤10 nm are formed. These features can be identified from an analysis of moire fringe contrast as phase of ZnO2.

Effect of solvent medium on the structural, morphological and optical properties of ZnS nanoparticles synthesized by solvothermal route

Different morphologies of ZnS have been synthesized by a facile solvothermal approach in a mixed solvent made of Ethylenediamine (EN) and distilled water. The effect of solvent medium on the structural, morphological and optical properties of ZnS nanoparticles were investigated. The formation mechanism of different morphologies was proposed based on the experiment results. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), Raman spectroscopy and UV-Vis-IR spectrophotometer. The results show that phase transformation is easily induced and there is a strong correlation between morphology and structure of the ZnS nanocrystals by changing the solvent. The results also show that we have successfully produced hexagonal phase ZnS nanorods with mixed solvent. The grain sizes in the range of 17–22 nm were obtained according to elaboration conditions. Raman spectra show the intense peak at 346 cm−1, which is a typical Raman peak of bulk ZnS crystal, no signature of secondary phases. The band gap of ZnS increased from 3.49 to 3.74 eV with an increase in the EN composition in the solvent, implying that the optical properties of these materials are clearly affected by the synthesis medium.

Structural evolution and optical properties of oxidized ZnS microrods

In this study, we present a simple and versatile way to growth and modify photoemission of high quality ZnS microrods by thermal evaporation method in combination with post oxidation in oxygen environment. The as-grown ZnS microrods show strong near edge luminescence doublets at room temperature indicating the high crystalline quality. Using ultrahigh-resolution scanning electron microscope integrated with energy microanalysis and cathodoluminescence capacity we elucidate the effect of oxidation temperature on microstructure surface, chemical composition and emission spectra of ZnS microrods. Under appropriate oxidation condition, the initial high quality ZnS microrods can be converted into ZnS/ZnO microrod heterostructures or optically active porous ZnO microrods. More particularly, we demonstrate that the emission wavelength of an oxygen-related defect could be tuned in between optical band-gap of ZnS and ZnO upon increasing the oxidation temperature. This research introduces a simple approach to synthesize and tune optical property of high quality ZnS crystals.