Emission Of ZnS Research Articles

Luminescence properties of blue–red emitting multilayer coated single structure ZnS/MnS/ZnS nanocomposites

Uncoated ZnS, MnS and ZnS/MnS/ZnS nanocomposites were successfully synthesized by chemical co-precipitation method in air atmosphere by varying the thicknesses of MnS layer. Characterization techniques such as X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV–visible absorption and photoluminescence (PL) spectroscopy were used to characterize the novel ZnS/MnS/ZnS nanocomposites. The obtained particles were highly crystalline and monodispersed with an average particles size of 4.5–6.5nm. The room temperature photoluminescence (PL) study of ZnS/MnS/ZnS nanocomposites showed an enhanced intensity with different concentration of manganese acetate. The presences of MnS layer in the nanocomposite have tuned the PL emission in the IR region. Addition of manganese acetate (0.1–0.4M) in the nanocomposite showed a distinct PL emission peak centered at 740nm i.e. in the red region with significant red shift. The PL emission of ZnS and MnS were tuned in the nonvisible IR region. It is shown that the variation in thickness of MnS layer leads to an enhanced photoluminescence intensity/efficiency of ZnS/MnS/ZnS nanocomposites.

Investigations of the thermal shift of Mn2+-related emission in ZnS:Mn2+ nanocrystals

The thermal shift (or temperature-dependence) of Mn2+-related emission (4T1→6A1) in nanocrystalline ZnS:Mn2+ are calculated by using a theoretical expression including both the static and vibrational mechanisms. In the calculation, the static part is estimated by means of the pressure-dependence of Mn2+-related emission. The calculated results suggest that the static part due to thermal expansion contributes about 70% and the vibrational part due to electron–phonon interaction contributes about 30% to the observed thermal shift. So the observed thermal shift cannot be reasonably explained by using only one of the two mechanisms. The electron–phonon coupling parameters are also obtained from the calculation. It is found that the true and rational electron–phonon coupling parameter α′ (≈350(20)cm−1) obtained from the present expression is much smaller than that (α≈1140(60)cm−1) obtained from the previous expression consisting of only the vibrational mechanism.

About the origin of center responsible for Cu-related blue emission band in ZnS:Cu

To choose among proposed in the literature models of the center responsible for Cu- related blue emission in ZnS:Cu (B-center), the technique of defect drift in external electric field was used. Doped with Cu zinc sulfide single crystals were investigated. After the action of direct electric field of (4–5) 102V/cm at 300°C blue emission was found to enhance near the cathode and to weaken near the anode. This effect was accounted for by the appearance of Cui+ ions due to dissociation of B-centers, following drift of these ions to the cathode and formation of additional B-centers in near cathode region. It was concluded that B-centers are close donor–acceptor pairs consisting of Cuzn acceptors and Cui donors.

On the luminescence enhancement of Mn2+ by co-doping of Eu2+ in ZnS:Mn,Eu

The photoluminescence and X-ray luminescence of ZnS:Mn, ZnS:Mn,Eu and ZnS:Eu were investigated and it was found that the luminescence intensity of Mn2+ in ZnS:Mn,Eu co-doped phosphors is highly dependent on the doping concentration of Eu2+. At the optimized Eu2+ concentration (0.2%), the photoluminescence of Mn2+ shows about a 5.5 times enhancement and its X-ray luminescence is enhanced by a factor of 2.5. Both wurtzite and zinc blend phases are present in the samples with wurtzite phase dominant. Co-doping of Eu2+ into ZnS:Mn does not change appreciably the ratio of the two phases or the Mn2+ emission luminescence lifetime; however, the doping of Eu2+ into ZnS:Mn does change the phonon activity. Furthermore, it was found that the defect-related blue emission of ZnS:Eu overlaps with the excitation bands of Mn2+ in ZnS:Mn and there is likely energy transfer from these defect states to Mn2+ in ZnS:Mn,Eu. This energy transfer and the phonon modification are considered to be the two main reasons for the luminescence enhancement and the intensity dependence of Mn2+ emission on Eu2+ doping concentration in ZnS:Mn,Eu.

Surface polarity induced three-dimensional wurtzite ZnS/ZnSxSe1−x nano-heterostructures with integrating emission property

By controlling the reaction conditions and molar ratio of precursors carefully, three-dimensional ZnS/ZnS0.3Se0.7 nano-heterostructures were synthesized via a simple two-step magnetic force assistant growth technique. Scanning electron microscopy, X-ray powder diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy were used to characterize and analyze the morphology, phase structure, crystallinity and composition of the as-prepared nano-heterostructures. Remarkably, the epitaxial ZnS nanoribbon is single crystalline and preserves the structure and orientation of the matrix ZnSxSe1−x nanobelt with an epitaxial relationship of (0001)ZnS//(0001)ZnS0.3Se0.7 and (100)ZnS//(100)ZnS0.3Se0.7. A polar-surface induced growth process for the three-dimensional nano-heterostructures is proposed according to the experimental results and crystallography relationship. This approach can offer a prevailing way to fabricate more complex three-dimensional nanostructures with built-in heterojunctions. Room temperature PL spectra were used to investigate the emission property of the as-prepared samples. The PL spectra of ZnSe and ZnSxSe1−x nanobelts show strong near bandgap emission, demonstrating a high crystal quality of these as-synthesized nanobelts. The PL spectrum of three-dimensional ZnS/ZnS0.3Se0.7 nano-heterostructures shows the near bandgap emission of ZnS and ZnS0.3Se0.7 simultaneously, demonstrating the incorporating function. These three-dimensional nano-heterostructures with unique structure and morphology can be used to investigate the incorporating function and find extensive applications in nanophotonics.

Expression of Concern: Luminescence study of monodispersed ZnS nanoparticles

Monodispersed ZnS nanoparticles have been successfully synthesized by a chemical precipitation method in an air atmosphere using polyvinylpyrrolidone (PVP) and sodium hexametaphosphate (SHMP) as surfactants. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR), UV-Vis optical absorption and photoluminescence (PL) spectra. Prepared surfactants capped ZnS nanoparticles are highly homogeneous and well dispersed. Optical absorption spectra showed a strong blue shift from the uncapped particles due to the quantum confinement effect. The capped ZnS emission intensity is enhanced than more the uncapped particles. The size of the synthesized particles is around 4-6.5 nm range.

CONTROLLED SYNTHESIS AND CHARACTERIZATION OF CERIUM-DOPED ZnS NANOPARTICLES IN HMTA MATRIX

Cerium-doped ZnS nanoparticles have been synthesized through hydrothermal method. The nanoparticles were stabilized using hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The average particle size of the prepared samples is about 2 nm. The structure of the as-prepared ZnS nanoparticles is cubic (zinc blende) as demonstrated by X-ray powder diffraction (XRD) and selected area electron diffraction (SAED) analysis. TEM results showed that the synthesized nanoparticles were uniformly dispersed in the HMTA matrix without aggregation. The UV–Vis absorption spectra of the prepared ZnS nanoparticles show a considerable blueshift in the absorption band edge compared to bulk ZnS indicating a strong quantum confinement effect. Formation of HMTA-capped ZnS nanoparticles was confirmed by FTIR studies. Photoluminescence studies showed that the relative emission intensity of Ce3+ -doped ZnS nanoparticles is higher than that of undoped ZnS nanoparticles, which is due to the enhancement of radiative recombination in the luminescence process. The PL spectra showed two emission peaks at around 420 nm and 442 nm, which may be attributed to deep-trap emission or defect-related emission of ZnS and presence of various surface states.

Self-organized hierarchical zinc phosphide nanoribbon–zinc sulfide nanowire heterostructures

Hierarchical Zn3P2 nanoribbon–ZnS nanowire heterostructures were synthesized by simple thermal evaporation of the mixture of ZnS and InP powders. Studies found that the synthesized hierarchical heterostructures consisted of single crystalline Zn3P2 nanoribbons with numerous single crystalline [0001]-oriented ZnS nanowires grown perpendicular to the Zn3P2 nanoribbons. The growth mechanism of the hierarchical heterostructures was investigated in detail by studying the intermediate samples synthesized at different times. Low-temperature cathodoluminescence properties of the heterostructures were investigated, where two emission bands centered at 600 nm and 790 nm were observed, corresponding to the defect-related emission of ZnS and band gap emission of Zn3P2, respectively. Single heterostructure-based devices were also fabricated to study their photoconducting properties, showing decent responses to lights with different wavelengths.

Enhanced Cu emission in ZnS : Cu,Cl/ZnS core–shell nanocrystals

ZnS : Cu,Cl/ZnS core-shell nanocrystals (NCs) have been synthesized via a facile aqueous synthesis method. The shell growth of the NCs was observed via a red-shift in the UV-Vis absorption spectra with increasing NC size. The Cu photoluminescence (PL) emission was enhanced by capping with a thin ZnS shell. The ZnS : Cu (0.2%) and ZnS : Cu (0.5%) show a more pronounced red-shift in the apparent PL peak position as well as a 37% and 67% increase in emission intensity, respectively, in comparison to the undoped NCs. The observed red-shift is mainly due to an increase in intensity of the Cu PL emission. The 1% Cu-doped NCs exhibit very little red-shift because the observed emission is dominated by the Cu-dopant and thus nearly independent of the size of the NCs. The increase in Cu emission is evidence that Cu atoms occupying non-emissive surface sites in doped ZnS NCs were encapsulated by the ZnS shell. Extended X-Ray Absorption Fine Structure (EXAFS) data also suggests that the Cu had slightly more neighbors upon growth of a ZnS shell, indicating its encapsulation into the core of the NCs. The EXAFS Zn edge data also indicate greater disorder in the ZnS structure when the shell is grown, which may be attributed to the ZnS shell being more amorphous than the core NCs. This study demonstrates that core-shell structures can be used as a simple and yet powerful strategy to enhance PL properties of doped semiconductor NCs.

Intense green emission of ZnS:Cu, Al phosphor obtained by using diode structure of carbon nano-tubes field emission display

ZnS:Cu, Al phosphor is prepared by conventional solid-state reaction and is confirmed as an efficient phosphor for field emission display (FED). Broad photoluminescence (PL) band centered at 528 nm is obtained from the phosphor. The ZnS:Cu, Al and carbon nano-tubes (CNTs) are screen-printed on indium tin oxide (ITO) substrate to prepare the anode and the cathode plates of FED, respectively. The luminous performance is studied by using a diode structure and is controllable by adjusting space distance between the anode and cathode plate as well as thickness of phosphor-layer on the anode plate. The optimized luminance is around 6231 cd m −2 when using a 0.25 mm spacer and applying an electric field of 6 V μm −1.

Growth, Cathodoluminescence and Field Emission of ZnS Tetrapod Tree‐like Heterostructures

AbstractWe report the growth mechanism, cathodoluminescence and field emission of dual phase ZnS tetrapod tree‐like heterostructures. This novel heterostructures consist of two phases: zinc blende for the trunk and hexagonal wurtzite for the branch. Direct evidence is presented for the polarity induced growth of tetrapod ZnS trees through high‐resolution electron microscopy study, demonstrating that Zn‐terminated ZnS (111)/(0001) polar surface is chemically active and S‐terminated (${\bar 1}$${\bar 1}$${\bar 1}$)/(000$\bar 1$) polar surface is inert in the growth of tetrapod ZnS trees. Two strong UV emissions centered at 3.68 and 3.83 eV have been observed at room temperature, which are attributed to the bandgap emissions from the zinc blende trunk and hexagonal wurtzite branch, indicating that such structures can be used as unique electromechanical and optoelectronic components in potential light sources, laser and light emitting display devices. In addition, the low turn‐on field (2.66 Vµm−1), high field‐enhancement factor (over 2600), large current density (over 30 mAcm−2 at a macroscopic field of 4.33 Vµm−1) and small fluctuation (∼1%) further indicate the availability of ZnS tetrapod tree‐like heterostructures for field emission panel display. This excellent field‐emission property is attributed to the specific crystallographic feature with high crystallinity and cone‐shape patterned branch with nanometer‐sized tips. Such a structure may optimize the FE properties and make a promising field emitter.

Influence of Surface Quenching Effects on Luminescent Dynamics of ZnS:Mn2+ Nanocrystals

A model describing surface quenching of isolated ion centres in nanocrystals is proposed based on the energy transfer between the doped ions and the nanocrystalline surface quenching centres. The quenching rate depends on the position of the ions in the nanocrystal, hence the decay curve under non-selective excitation is generally nonexponential The decay curve calculated with this model is in good agreement with that of the 4T1 → 6A1 emission in ZnS:Mn2+ nanocrystals.

Surface Passivation and Photoluminescence of Mn-Doped ZnS Nanocrystals

Enhanced photoluminescence (PL) is reported from Mn-doped ZnS nanocrystals (NCs) capped with ZnS (ZnS:Mn/ZnS core-shell NCs) and thioglycolic acid (TGA) (ZnS:Mn/ZnS core-shell NCs dispersed in an alkaline TGA solution). The NCs were prepared using a reverse micelle route. Comparing with initial ZnS:Mn core NCs, the ZnS:Mn/ZnS core-shell NCs exhibit much stronger orange PL (~580 nm). This is presumably the result of effective passivation of quenching ZnS:Mn NCs surface states by a pure ZnS shell. As for TGA-capped ZnS:Mn/ZnS core-shell NCs, the parallel decrease of a defect-related emission of ZnS is associated with the formation of a shell surface layer of TGA-Zn complexes. In summary, the combination of ZnS shells with TGA ligands was demonstrated to yield ZnS:Mn NCs with narrow size distribution and intense PL.

Thermofield Cr+ →Cr 2+ recharging resulting in anomalous intensification of Cr2+ emission in ZnS:Cr thin-film electroluminescent structures

Thermofield Cr+ →Cr 2+ recharging resulting in anomalous intensification of Cr2+ emission in ZnS:Cr thin-film electroluminescent structures

Photoluminescence decay kinetics of doped ZnS nanophosphors

Doped nanophosphor samples of ZnS:Mn, ZnS:Mn, Co and ZnS:Mn, Fe were preparedusing a chemical precipitation method. Photoluminescence (PL) spectra were obtained andlifetime studies of the nanophosphors were carried out at room temperature. To the best ofour knowledge, there are very few reports on the photoluminescence investigations ofCo-doped or Fe-doped ZnS:Mn nanoparticles in the literature. Furthermore, there isno report on luminescence lifetime shortening of ZnS:Mn nanoparticles dopedwith Co or Fe impurity. Experimental results showed that there is considerablechange in the photoluminescence spectra of ZnS:Mn nanoparticles doped with X(X = Co, Fe). The PL spectra of the ZnS:Mn, Co nanoparticle sample show three peaks at 410, 432and 594 nm, while in the case of the ZnS:Mn, Fe nanoparticle sample the peaks areconsiderably different. The lifetimes are found to be in microsecond time domain for 594 nmemission, while nanosecond order lifetimes are obtained for 432 and 411 nm emission inZnS:Mn, X nanophosphor samples. These lifetimes suggest a new additional decay channelof the carrier in the host material.

Encapsulation of ZnS:Mn2+ nanocrystals with diblock copolymers

AbstractThe encapsulation of the nanocrystalline manganese‐doped zinc sulfide (ZnS:Mn) in poly(styrene‐b‐2vinylpyridine) (PS‐PVP) diblock copolymers is reported. Below the critical micelle concentration in the absence of nanocrystals (NCs), inverse micelles of PS‐PVP were induced by adding ZnS:Mn NCs, the presence of which was confirmed by scanning force microscope and dynamic light scattering. In toluene, a PS‐selective solvent, the less‐soluble PVP blocks preferentially surround the ligand‐coated ZnS:Mn NCs. For PS‐PVP encapsulated ZnS:Mn NCs, the ratio of blue emission to orange emission of ZnS:Mn NCs is dependent on both the concentration of PS‐PVP and the solvent quality. The pyridine of PVP blocks form complexes with the Zn atoms via the nitrogen lone pair and thus the sulfur vacancies are passivated. As a result, the defect‐related blue emission is selectively quenched even when the micelles are not formed. As the concentration of PS‐PVP encapsulating the ZnS:Mn NCs increases, the intensity of blue emission decreases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3227–3233, 2006

Manganese doping and optical properties of ZnS nanoribbons by postannealing

Manganese (Mn) doping of ZnS nanoribbons was achieved by simple thermal annealing. Upon heating ZnS nanoribbons with MnS powder up to 700°C, the intrinsic photoluminescence (PL) of the annealed nanoribbons disappeared and a new PL peak at 585nm gradually emerged. Significantly, the annealing process induced no detectable change in the morphology and uniform hexagonal wurtzite 2H structure of the single-crystal ZnS nanoribbons. The PL peak at 585nm is attributed to Mn dopant and confirms Mn incorporation in ZnS because (1) the peak appears only when ZnS ribbons were annealed with MnS, but does not appear without MnS, (2) its intensity increases with increasing annealing temperature, which is consistent with increased incorporation of Mn2+ ions, and (3) its position is similar to that of Mn-related emission in ZnS, and is independent of the measuring temperature and excitation power. This work demonstrates the capability of doping nanostructured materials by simple postannealing treatment.

Synthesis and Luminescence of ZnMgS:Mn<SUP>2+</SUP> Nanoparticles

Efficient green emission from ZnMgS:Mn2+ nanoparticles prepared by co-doping Mg2+ and Mn2+ ions into ZnS lattices has been observed. The synthesis is carried out in aqueous solution, followed by a post-annealing process, thus showing the features of less complexity, low cost, and easy incorporation of dopants. In comparison with the emission of ZnS:Mn2+ nanoparticles, which is located generally around 590 nm, the photoluminescence of ZnMgS:Mn2+ nanoparticles is blue-shifted by 14 nm in wavelength, leading to the enhanced green emission. The X-ray diffraction, electron spin resonance, and pressure dependent photoluminescence measurements suggest that the change of the crystal field caused by Mg2+ ionic doping and the lower symmetry in the nanoparticles may account for the blue-shift of the photoluminescence. The ZnMgS:Mn2+ nanoparticles with 1% Mn2+ doping exhibit the strongest luminescence, which could potentially meet the requirements for the construction of green light emitting diodes.

Optical and magnetic properties of ZnS nanoparticles doped with Mn 2+

ZnS:Mn nanoparticles of the cubic zinc blende structure with the average sizes of about 3 nm were synthesized using a coprecipitation method and their optical and magnetic properties were investigated. Two emission bands were observed in doped nanoparitcles and attributed to the defect-related emission of ZnS and the Mn 2+ emission, respectively. With the increase of Mn 2+ concentration, the luminescence intensities of these two emission bands increased and the ZnS emission band shifted to lower energy. Based on the luminescence excitation spectra of Mn 2+, the 3d 5 level structure of Mn 2+ in ZnS nanoparticles is similar to that in bulk ZnS:Mn, regardless of Mn 2+ concentration. Magnetic measurements showed that all the samples exhibit paramagnetic behavior and no antiferromagnetic interaction between Mn 2+ ions exists, which are in contrast to bulk ZnS:Mn.

Pressure and Temperature Effects on Point-Defect Equilibria and Band Gap of ZnS

The pressure (100–200 MPa) and temperature (900–1100°C) effects on the equilibria of native point defects and background impurities in Zn-enriched ZnS are studied using cathodoluminescence and transmission spectra. The optimal conditions are found under which high pressures and temperatures accelerate migration of defects and impurities. The associated structural and compositional changes are studied by scanning electron microscopy. The increase in the concentration of dissolved oxygen at high pressures and temperatures is accompanied by a reduction in the band gap of ZnS, growth and blue shift (to 395–400 nm) of the shorter wavelength component of the SA blue emission in ZnS, and quenching of the longer wavelength component (445 nm). In addition, at 300 K a free-exciton bandI1 emerges at 342 nm. It is shown that the data available in the literature can be used to evaluate the concentration of dissolved oxygen in ZnS · O from its band gap. The effects of different oxygen species on the transmission of ZnS are studied in the range 3.5–15 μm.