ZnS Phase Research Articles

An insight into the structure, luminescent characteristics and Judd-Ofelt analysis of (1-x) ZnS-(x) Dy2O3 phosphors

We report a white light emitting of (1- x) ZnS - (x) Dy2O3 with x = 0, 0.1, 0.2 and 0.3 phosphor synthesized via conventional solid state reaction method. The crystal structure, modes of vibrations, morphology, NIR-UV absorption and luminescence characteristics were discussed. The X-ray diffraction study confirmed the single phase of hexagonal ZnS and cubic Dy2O3 structure. The intensity parameters Ω2, Ω4 and Ω6 were estimated for x = 0.1, from the optical absorption spectra using Judd-Ofelt theory, since the optimal doping concentration is about 10mol%. The optical band gap energy of the samples varied from 3.41 to 3.49 eV. The photoluminescence spectra has an intense strong emission at 582 nm corresponding to 4F9/2 → 6H13/2 transition due to a forced electric dipole (ED) allowed transition with selection rule ΔL = 2 and ΔJ = 2. The transition radiative parameter (AR) and the stimulated emission cross section, σe values suggested that (1- x) ZnS - (x) Dy2O3 with x = 0.1 phosphor material is suitable for white LED applications. The nephelauxetic ratio and the bonding parameter of concentration x = 0.1 were calculated. The negative value of bonding parameter indicated that Dy3+ ion and ZnS material is bonded ionically. The CIE chromaticity coordinates, Yellow to Blue intensity ratio, Color Purity and Correlated Color Temperature were also estimated. The CIE coordinates of the samples lie in the white light region and this type of white light luminescence phosphors could be promising phosphors for w-LEDs and optoelectronic devices applications.

Improved self heating and optical properties of bifunctional Fe3O4/ZnS nanocomposites for magnetic hyperthermia application

Opto-magnetic Fe3O4/ZnS nanocomposite was synthesized by the co-precipitation method. The structural, morphological, optical and magnetic characterizations were performed by XRD, HRTEM, FTIR, PL, UV–Vis and VSM techniques. The existence of both the spinal cubic phase of Fe3O4 and the zinc blende phase of ZnS in the prepared nanocomposite was confirmed by XRD. HRTEM image depicts the formation of the ZnS shell around the Fe3O4 core. FTIR spectra revealed the incorporation of ZnS nanoparticles on the surface of Fe3O4 nanoparticles. UV–Vis spectra illustrate the decreasing band gap of the ZnS nanoparticles with the trend of increasing the size of ZnS nanoparticles due to the quantum size effect. PL spectra manifest the red shift in the nanocomposite due to a higher dielectric environment compared to the ZnS nanoparticle. The VSM study signifies the higher coercivity but lower saturation magnetization of the nanocomposite compared to the nanoparticle. The increasing heating efficiency of Fe3O4/ZnS nanocomposite than Fe3O4 nanoparticles was quantified by their respective SAR values which are found to increase in the ranges from 24–52 (w/g) (Fe3O4) to 31–79 (w/g) (Fe3O4/ZnS.) with respective concentrations. The above results speculate that the prepared nanocomposite is a decent candidate for magnetic hyperthermia applications to destroy the tumor and cancer cells.

Synthesis of composite nanopowder through Mn doped ZnS-CdS systems and its structural, optical properties

The design of new functional materials is a driving force for the development of advanced materials chemistry. Out of many new-style substances, the fabrication of composite nanopowders possesses attracted considerable attention in industry and academia, as they often exhibit significant advancement in the effect of materials estimate to typical macro and micro combinations. The developed ZnS-CdS composite nanopowders with unique and tailored properties for various applications in the fields of surface-improved catalysis, photonic crystals, nano-electronic and LED appliances, etc. In practice, Mn2+ ions doped ZnS-CdS mixed nanopowders are held in the lead 2–6 bulk solid-state mixture by the control bandwidth of 3.7 and 2.4 eV for ZnS and CdS at room temperature. The present research deals with the preparation, structural and spectral characterizations of transition metal ions doped ZnS-CdS composite nanopowders. X-ray diffraction patterns indexed to the cubic crystalline phase of both ZnS and CdS and the average crystallite size is evaluated using Scherer's formula is in the class of nanometer-range. Morphological images of Mn2+ ions ZnS-CdS composite nanopowders are in unequal mode structure with agglomerated fragment with nano-size. The spectra of optical absorption and EPR reveal the distorted octahedral symmetry. By correlating optical and EPR data, the evaluated bonding parameters suggested that the bonding between the doped ions and ligands are partially covalent. The luminescent spectrum gives the emission bands in UV, blue, and green regions. The calculated CIE chromaticity coordinates from emission spectra give the color perception of the prepared nanocomposites. FTIR spectrum shows the essential oscillating function of ZnS, CdS plus additional active groups. Enhanced paramagnetic nature is observed at room temperature of the prepared material which is intrinsically caused by exchange coupling between the spin of the carriers and local magnetic moments.

Solid state low temperature synthesis approach for ZnO-ZnS nanoheterostructure with functionality as a photocatalyst for H2 production and for DSSC

Herein, we demonstrate a facile, template free, scalable, solid-solid, single step synthesis approach to produce ZnO/ZnS nanoheterostructure. Commercially available ZnO and thiourea have been used as precursors. Interestingly, it is observed that ZnO particle is covered with ZnS and the ZnS shell thickness can be varied depending on the sulfidation time. The crystal structures, morphology of samples are verified by XRD, FETEM and EDX. The XRD results show the mixed phases of hexagonal ZnO and ZnS. The broad peak of ZnS clearly reveals the nanocrystalline nature and also increase in intensity of peak with respect to sulfidation time. The optical spectra of the samples exhibits two band absorption edges and blue shift in the absorption edge depending on the ZnS thickness deposited. Particle size of the ZnS (5–3 nm) coated on the ZnO by varying the sulfidation time influences the performance of the DSSC and photocatalytic H2 evolution from water has been investigated, systematically. The DSSC performance of ZnO/ZnS nanoheterostructure shows maximum efficiency of 3.30% with increment in Jsc (9.04 mA/cm2). The performance is much better than pristine ZnO and earlier report of ZnO-ZnS nanostructure. This good performance is due to excellent light absorbing capability of the ZnO/ZnS nano heterostructure by providing ZnO core by providing easy electron transfer at the interface and the ZnS shell facilitate to reduce the recombination of diffuse electrons with either the dye or the electrolyte. The H2 evolution rate reported herewith is 3209 and 1685 μmol h−1g−1 under UV and Natural sunlight, respectively which is significantly higher than pristine ZnS and ZnO. The H2 evolution rate increases with decrease in particle size of ZnS which is quite ovibius because lowering particle size exhibits increase in surface area. The fabrication of ZnO/ZnS nanoheterostructure is the simple and cost effective, which can open new avenues strategy for large scale applications of the novel materials in the energy storage and photovoltaic devices.

Phase diagram of the Ag2SnS3–ZnS pseudobinary system for Ag2ZnSnS4 crystal growth

The phase equilibrium of the Ag2SnS3–ZnS pseudobinary system for the growth of Ag2ZnSnS4 (AZTS) crystals was investigated using the equilibration-quenching technique. The growth mechanism of AZTS follows the peritectic reaction liquid phase + ZnS phase ↔ AZTS phase, which occurs at a composition of ~20 mol% ZnS and a temperature of approximately 700 °C. The AZTS polycrystalline sample was obtained from the stoichiometric melt growth. The kesterite structure of the AZTS sample without secondary phases was identified by a combination of X-ray diffraction and Raman spectroscopy measurements. The electron carrier concentration and conductivity, determined by the Hall effect measurement, were (3.0–6.3) × 1015 cm−3 and (5.6–9.2) × 10−4 S/cm, respectively. The slightly Zn-rich and S-poor composition led to n-type conduction in the AZTS because of the dominant Zn antisites on Ag (ZnAg) and S vacancy (VS) defects. Therefore, this study can make a significant contribution to the research and application of AZTS materials.

Structural, Optical and Photocatalytic Characterization of ZnxCd1−xS Solid Solutions Synthetized Using a Simple Ultrasonic Radiation Method

A simple ultrasonic radiation method was employed for the preparation of zinc and cadmium sulfide solid solution (ZnxCd1−xS; x = 0–0.25 wt.%) with the aim to investigate its efficiency for H2 production via a visible light-driven water-splitting reaction. The catalyst characterization by X-ray diffraction confirmed the formation of solid solution (ZnxCd1−xS) between CdS and ZnS phases. All catalysts exhibited hierarchical morphology (from SEM and TEM) formed by aggregated nanoparticles of ZnxCd1−xS solid solution with crystals showing mainly (111) planes of cubic CdS phase. The crystal size linearly decreased with an increase in Zn incorporation in the crystal lattice (from 4.37 nm to 3.72 nm). The ZnxCd1−xS photocatalysts showed a gradual increase in the H2 evolution, with an increase in the Zn concentration up to 0.2 wt.% making the most effective Zn0.2Cd0.8S catalyst toward H2 production. From the catalyst activity–structure correlation, it has been concluded that the twin-like CdS structure, the (111) plane and specific morphology are the main factors influencing the catalyst effectivity toward H2 production. All those factors compensated for the negative effect of an increase in band gap energy (Ebg) after ZnS incorporation into solid solution (from 2.21 eV to 2.34 eV). The effect of the catalyst morphology is discussed by comparing H2 evolution over unsupported and supported Zn0.2Cd0.8S solid solutions.

Effect of europium on the blue–green emission of ZnS thin films by polyol and dip-coating technique

This work reports the effect of annealing treatment (550, 650, and 750 °C) and europium concentration (1-7 at.%) on the structural, morphological, and optical properties of ZnS:Eu3+ thin films synthesized by the polyol method and dip-coating technique. The films were indexed to the zinc-blende phase of ZnS with crystallite size ranging from 2-7 nm and exhibited preferential orientation at the (111) plane according to the XRD analyses. The SEM and AFM images indicate homogeneous, flat, crack-free, compacted films, with pyramidal grain shape and particle size distribution about ∼25 nm. High transmittance in the visible region (above 80 %) and band gap (3.75-3.9 eV) computed by the Tauc model were obtained by UV–VIS spectroscopy. The PL spectra show the emission bands related to radiative recombination involving defect states, particularly, zinc and sulfur vacancies. The PL spectra also indicate that the higher the europium concentration, the higher the emission light intensity in the blue–green regions. At the same time, the typical 5D0→7F2 transition from Eu3+ is barely noticeable due to a poor energy transfer from the ZnS host to the Eu ions. On the other hand, by increasing the annealing temperature from 550 to 750 °C, a 2.5-fold decrease in the emission intensity is recorded.

Correlation with surface defects and maiden observation of disorder activated phonon in cubic ZnS QDs.

Defects and deformation potential in quantum dots (QDs) were found to control the Raman modes however the disorder activated phonon (DAP) mode could not be seen in the cubic phase ZnS. With a maiden observation of a DAP mode the crucial role of surface defects, in particular, elemental 'S' is reported. The DAP mode was seen with significant intensity at 153cm-1 along with the LO mode at 347cm-1 for the cubic ZnS. ZnS nanoparticles (NPs) of 3 to 5nm were synthesized to understand origin of the DAP mode and its correlation with defects. The strongest DAP mode was observed in ZnS QDs of 3nm size which showed the highest surface defects, in particular, the elemental type sulfur as revealed by the photoluminescence study. With increase in crystal size, the bulk-like property set in with the appearance of a weak DAP mode. Further, the reason behind the unclear observation of the mode in a cubic ZnS crystal near room temperature and effects of unaltered surface defects were investigated by the chemical functionalization with oleic acid and the heat treatment studies. The results revealed existence of a strong correlation between surface defects and synthesis conditions for observation of a DAP peak in cubic ZnS NPs.

Structural, optical, and electronic properties of non-stoichiometric nano-ZnS1−x: Mnx

Non-stoichiometric ZnS1−x:Mnx nanomaterials were prepared using a thermolysis procedure by decreasing the stoichiometric amount of thiourea relative to the amount of zinc acetate as starting precursors: Zn(Ac)/(1−x) thiourea in the presence of (x) manganese acetate (x = 0, 0.01, 0.03, 0.05, and 0.1). Rietveld X-ray diffraction analysis was used to examine the structural modification in the ZnS lattice induced by sulfur deficiency and Mn2+ incorporation. The samples with x ≤ 0.01 exhibited a single ZnS zincblende phase, while other samples, x ≥ 0.02, have two phases ZnS and ZnO with different percentages. The lattice parameter of the system is governed by the Mn and S amounts in the matrix. A high-resolution transmission electron microscope established the quantum dot nature of the system. Fourier-transform infrared technique confirmed the presence of ZnS and ZnO phases in higher Mn-doped ZnS samples. The bandgap obtained from UV–vis analysis showed non-monotonic dependence on Mn content; it initially decreased and then increased to form a bandgap “bowing.” Photoluminescence analysis revealed that the emission colors depended on the amount of Mn doping in the matrix. The PL intensity raised for all Mn-doped samples as compared with the pristine sample reached its maximum value for the 3% and 5% Mn samples. The PL exhibited a red shift for the high dopant amount of Mn. Density function theory calculation was used to explore the electronic and optical characteristics of pure phases in ZnS1−xMnx system.

Phase relationships in the system ZnS-CuInS2: Insights from a nanoscale study of indium-bearing sphalerite

Abstract Micrometer- to submicrometer-scale indium-rich domains are preserved within sphalerite included in hornfels-hosted pyrrhotite from the Dulong polymetallic skarn, Yunnan, China. The nano-mineralogy of the ZnS-bearing blebs was investigated using scanning transmission electron microscopy on thinned foils extracted in situ from pyrrhotite. Indium incorporation in sphalerite occurs via the coupled substitution 2Zn2+ ↔ Cu+ + In3+; the results thus allow insights into phase relationships in the system ZnS-CuInS2 in which solubility limits are debated with respect to a cubic to tetragonal phase transition. The highest concentrations of In are measured in basket-weave domains from the smallest ZnS blebs or from un-patterned areas in coarser, irregular ZnS inclusions in pyrrhotite. Indium-rich domains contain 17–49 mol% CuInS2, whereas In-poor sphalerite contains <5 mol% CuInS2. Atomic-scale metal ordering observed in In-(Cu)-rich ZnS domains was modeled as mixed sites in a cubic structure with P43m symmetry and empirical formula [(Cu,In,Zn)3(Zn0.5Fe0.5)]4S4. This sphalerite modification is distinct from the cubic-tetragonal phase transition reported elsewhere for analogous, synthetic phases with abundant planar defects. The Zn1.5Fe0.5CuInS4 nanophase described here potentially represents a Fe-bearing polymorph of Zn2CuInS4, considered as an end-member in the sakuraiite solid-solution series. At ≤50 mol% CuInS2 in the ZnS-CuInS2 system, incorporation of In via coupled In+Cu substitution is promoted within a cubic ZnS phase with lower symmetry than sphalerite rather than into the spatially coexisting chalcopyrite of tetragonal symmetry. Solid-state diffusion accounts for phase re-equilibration resulting in the basket-weave textures typical of In-(Cu)-rich domains in the smallest blebs, whereas fluid percolation assists grain coarsening in the irregular inclusions. The results show evidence for the existence of a more complex phase transition than previously recognized from experimental studies, and, intriguingly, also to a potential eutectic in the system ZnS-CuInS2. Pyrrhotite-bearing hornfels in skarns may concentrate In and other critical metals hosted in sphalerite and related sulfides due to the efficient scavenging from fluid by these minerals and the subsequent preservation of those included phases by sealing within the pyrrhotite matrix.

Improved Structural, Optical and Photoluminescence Properties of EDTA Capped Zinc Sulfide Nanoparticles for Optoelectronic Applications

In the present study, ZnS nanoparticles have been synthesized via a simple and cost effective facile chemical co-precipitation method using ethylenediaminetetraaceticacid (EDTA) as capping or stabilizing agent. The role of EDTA was to stabilize the nanoparticle against aggregation and also to provide chemical passivation that leads to a significant influence on the improved structural, optical and photoluminescence properties of nanoparticles. The average grain size of the prepared nanoparticles calculated from the XRD pattern using Scherrer’s formula is about 3–5 nm, which exhibit cubic zinc blende structure. The SAED pattern exhibits three rings corresponding to (111), (220) and (311) planes respectively, which are in good agreement with the cubic phase of ZnS. The UV–Vis absorption results revealed that the EDTA capped ZnS nanoparticles exhibit strong quantum confinement effect as the optical band gap energy increased significantly compared to the uncapped and bulk ZnS. From FTIR analysis, the formation of EDTA capped ZnS nanoparticles were confirmed. Fluorescence spectra show that the EDTA capping increases the PL intensity compared to uncapped ZnS nanoparticles. From the Raman studies, the appearance of multiple resonance raman peaks show that the prepared EDTA capped ZnS nanoparticles exhibit good optical quality.

ZnS:Cu powders with strong visible-light photocatalysis and pyro-catalysis for room-temperature dye decomposition

In this work, strong visible-light photocatalysis and pyro-catalysis for dye decomposition was observed in hexagonal wurtzite phase ZnS:Cu. As described herein, ZnS:Cu ceramic is shown to be a visible-light-responsive material with a band gap of ~2.77 eV. Under visible-light irradiation, the photocatalytic decomposition ratios of ZnS:Cu on 5 mg/L Rhodamine B, methylene blue, and acid orange 7 solutions reach 99.2%, 95.9%, and 78.8%, respectively. With respect to pyro-catalysis results, the decomposition ratio for acid orange 7 in the same concentration is 82.2%. For photo-/pyro-bi-catalysis, the decomposition ratio can reach ~95%. In summary, the ZnS:Cu ceramics exhibit strong visible-light photocatalysis and pyro-catalysis, making it a viable solution for decomposing synthetic dyes wastewater through utilizing the visible-light energy and cold-hot cycling.

Etching process optimization of non-vacuum fabricated Cu2ZnSnS4 solar cell

Thin-film solar cell based on kesterite material Cu2ZnSnS4 (CZTS) is one of the third generation prospective solar cells replacing commercial Cu(Inx, Ga1−x)S2 (CIGS) material. However, the substitution of rare In and Ga material by Zn and Sn still requires further fabrication optimization. The secondary phases that formed during the fabrication process might have prohibited cell performance. Therefore, this work is essential to focus on introducing the etching process using 5% HCl with an etching time of 0, 100, 300, 480, and 600 s in order to minimize the secondary phases of Cu2S, SnS. SnS2, and ZnS during non-vacuum fabrication of Cu2ZnSnS4 kesterite. This Cu2ZnSnS4 active material works as a p-type semiconductor in thin layer solar cells. The film was deposited by the spin coating method with the standard structure of Mo/Cu2ZnSnS4/CdS/AZO/Ag. Characterization was carried out by X-ray diffraction (XRD) testing, scanning electron microscope–energy dispersive X-ray spectroscopy (SEM–EDX), UV–Vis spectroscopy, Tauc Plot analysis, and light-harvesting efficiency. The best results showed that the introduction of etching treatment using 5% HCl for 300 s in the CZTS layer has successfully reduced the secondary phases of ZnS, Cu2S, and SnS2 by 28.9, 5.8, and 0.3%, respectively. This absorber layer has contributed to achieving the maximum light-harvesting efficiency (LHE) of 95.2% with a bandgap of 1.76 eV. Interestingly, the treatment does not significantly contribute to changing the surface morphology and the grain size of Cu2ZnSnS4 kesterite film, but it affects the pores on the surface of the absorber layer due to the ZnS secondary phase reduction.

Synthesis of Mn-Doped ZnS Nanoparticles and Its Characterization

ZnS powders doped with manganese (ZnS:Mn) was synthesized by the sol gel method. The structural and optical characteristics are studied using various techniques. Analysis with X-ray diffraction shows that cubic ZnS phase is formed with average crystallite sizes varying between 10 nm and 13 nm. There is no phase transformation due to Mn2+ doping. The formation of ZnS was confirmed by X-ray photoelectron spectroscopy (XPS) measurement. TEM images indicated the spherical shape of the nanoparticles. However, optical study has shown a strong reflectance in the visible range. The band gap (Eg) of ZnS:Mn is varied between 3.51 eV and 3.56 eV. The photoluminescence properties of ZnS:Mn nanopowders were studied.

Bioprecipitation of As4S4 polymorphs in an abandoned mine adit

Opportunities to study the anthropogenic cementation zones within permanently flooded mine works, where toxic elements accumulate by processes not fully described, are generally very rare. We examined macroscopic arsenic sulfide deposits inside a decomposed timbering of an abandoned mine adit, which had been flooded for 75 years. Bonazziite (β-As4S4) was always the dominant mineral in the deposits (up to 96.5%), while realgar and the ZnS phase were present in minor amounts. These findings differ from near-surface environments, where the most common biogenic As sulfide is realgar and other polymorphs are usually present in trace amounts only. Bonazziite was chemically highly pure with an average As/S molar ratio 0.9. It was 34S depleted compared to both aqueous sulfate and primary sulfides, which is consistent with biogenic sulfur reduction. Sulfide encrustation was confined to individual wood tracheids, indicating the extent of microenvironments that were oversaturated with respect to these minerals. The sulfides were accompanied by older gypsum and younger arsenian schwertmannite indicating complex succession of the redox conditions within the timbering. Authigenic electrum was found in one sample. Analysis of microbial communities revealed the dominance of sulfate reducers and fermenting microorganisms within the timber, similar to realgar-precipitating spots in wetland soils as previously documented. An anoxic environment in the mine water was maintained by autotrophic iron oxidation. The results suggest that a highly reduced microenvironment embedded in anoxic, but relatively oxidized surroundings is the key feature of the realgar and bonazziite-precipitating systems.

Crystal engineering of ZnS by cationic and anionic surfactant-cum-solvent

High temperature (1020 °C) wurtzite phase of ZnS is highly valuable multifunctional wide-band gap semiconductors. However it is difficult to stabilized wurtzite phase at room temperature. In the present study, the high temperature phase is successfully stabilized at low temperature (120 °C) in presence of cationic surfactant-cum-solvent like ethanolamine (ENA) and Oleylamine (OLA). While, the use of anionic surfactant likes ethylenediamine tetra acetic acid (EDTA) could not induce cubic to wurtzite phase transformation in ZnS. X-ray diffraction study confirms the cationic surfactant-mediated phase transformation of ZnS. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images shows nanoscale dimensions of as synthesized ZnS. The coupling between surfactant molecules with ZnS is confirmed by Fourier Transform Infrared spectroscopy. A significant reduction in the phase transition temperature of ZnS from 1020 to 120 °C is achieved as compared to the bulk transition temperature (1020 °C). The role of cationic and anionic surfactants-cum-solvent on mechanisms of phase transformations of ZnS is discussed.

Fabrication of Cu2ZnSnS4 Thin Films from Ball-Milled Nanoparticle inks under Various Annealing Temperatures

Cu2ZnSnS4 (CZTS) has been recognized as a promising thin-film absorber material of chalcopyrite-related solar cells. A two-stage method for fabricating CZTS films using CZTS nanoparticles was developed. Nanocrystal inks fabricated by a ball-milling method was utilized to °C deposit CZTS precursors by spin-coating approach. The CZTS precursors were annealed in the sulfur atmosphere under different annealing temperatures ranging from 550 °C to 650 °C. Influences of annealing temperature on grain growth, composition, crystallinity, and photovoltaic properties of CZTS films were characterized. With the increase of annealing temperature, grain growth was enhanced, while the sulfur atomic ratio fist increased then decreased. The crystallinity of the films was significantly improved after the annealing, and the obvious peak of the secondary phase of ZnS, were observed from the X-ray diffraction results, when the annealing temperature increased to 625 °C. However, the secondary phase was not detected from the surface Raman spectrum. Through comparing the Raman spectrum of different areas of the CZTS film, secondary phases of ZnS and SnS were observed, indicating the decomposition of CZTS films, due to the high temperature. The highest conversion efficiency of 7.5% was obtained when the annealing temperature was 600 °C.

Study on sputtering Zn(O,S) buffer layers for eco-friendly Cu(In,Ga)Se2 solar cells

An eco-friendly Zn(O,S) film with a wider band gap is emerging as one of the promising Cd-free replacement material, which can be deposited by radio frequency sputtering. The effect of sputtering pressure on the Zn(O,S) films properties and the devices performance are studied systematically. At high pressure, the ZnS phase is found in the Zn(O,S) films resulting in a higher barrier at Zn(O,S) /CIGS interface which would lead to a low recombination activation energy (Ea). By reducing sputtering pressure, single phase of Zn(O,S) films are conducive to carrier transport as well as promote the films electric properties, ultimately improving the performance of Zn(O,S)/CIGS solar cells.

Synthesis of dual-emission Ag- and Mn-codoped Zn-In-S nanocrystals and their optical radiometric temperature sensors

In this work, a facile approach to synthesize the Ag- and Mn-codoped Zn-In-S nanocrystals (NCs) with dual emissions as ratiometric temperature sensors is reported. The as-synthesized codoped Zn-In-S NCs have a uniform size distribution and exhibit a zinc blende ZnS phase structure. Moreover, the as-produced codoped NCs show dual emission peaks which center at green and orange-red regions and have a photoluminescence quantum yield (PL QY) up to 45%. The time-resolved PL spectroscopy and X-ray photoelectron spectroscopy characterizations reveal that the dual emissions of these NCs are derived from the intrinsic emission of Ag+ and Mn2+, respectively. Moreover, the relative intensity ratio of dual emissions can be tailored by adjusting the Ag and Mn doping concentrations. The as-built ratiometric temperature sensors based on the codoped NCs exhibit a thermometric sensitivity of ~ 0.17% K-1 over a broad window of 80–200 K, suggesting that these codoped Zn-In-S NCs are promisingly used for bio-optical ratiometric temperature sensing.

Ellipsometric evaluation and morphology of mixed zinc sulfide/zinc oxide and zinc oxide nanostructures synthesized at various temperatures

The aim of this work was to carry out systematic studies of how synthesis temperatures affect the morphology and properties of mixed zinc sulfide/zinc oxide (ZnSxOy and ZnO) nanostructures, and to get reliable data on optical constants of ZnSxOy and ZnO nanowires/nanobelts (NW/NB) for the use in device applications. ZnSxOy and ZnO NWs/NBs were fabricated using vapor transport in an open-end tube. Mixed ZnS0.47O0.62NWs was obtained at the synthesis temperature of 850 °C. The sulfur content disappeared as the temperature increased to 950 °C and 1050 °C and the morphology changed to a mixture of NW/NB. The NW prepared at 850 °C were indexed as mixed phases of hexagonal ZnS and hexagonal ZnO structures. The NW/NB prepared at 950 °C and 1050 °C were indexed as pure hexagonal ZnO structures. The thickness, surface roughness, and optical constants of the synthesized nanostructured samples were extracted from measurements of spectroscopic ellipsometry. A two-layers model was proposed to fit the calculated data to the measured ellipsometric spectra. The estimated band gap values of the prepared nanostructures lay 0.66–0.79 eV below the bulk ZnO value due to the lower oxygen content present in the samples and the stresses built in the samples during preparation.