ZnSe Samples Research Articles

Absorption spectra and nonlinear transmission (at ) of a diffusion-doped single crystal

Transmission spectra of a ZnSe sample diffusion-doped with ions have been measured in the wavelength range . A broad absorption band in the range has been observed in both doped and undoped regions of the sample. This band is possibly due to deviations from stoichiometry in the course of diffusion doping. The transmission of the sample at a wavelength of has been measured at various dopant concentrations and high peak pulse intensities (up to ). The samples have been shown to be incompletely bleached: during a laser pulse, the transmission first increases, reaches a maximum, and then falls off. Our results suggest that the incomplete bleaching cannot be accounted for by excited-state absorption. The incomplete bleaching (as well as the transmission maximum) is due to the heating of the sample, which leads to a reduction in upper level lifetime and, accordingly, to an increase in absorption saturation intensity.

Studies on Spin Orbit Splitting and Dual Mode Phonon Vibrations in ZnS x Se1−x Ternary Alloys Films with Varying Se Concentration

ZnS x Se1−x (x = 0, 0.41, 0.51, 0.91, 1) ternary alloy thin films with variable structural, optical and vibrational properties were prepared by thermal evaporation of solvothermally synthesized ZnS-ZnSe nanocomposite powders. The deposited films were uniform and have zinc-blende structure with (111) orientation. Variation of lattice parameter with composition was slightly non-linear with a bowing parameter of 0.12 Å. Spin orbit (SO) splitting of the valence band was observed in binary ZnSe and ternary samples with large Se atomic concentration such as ZnS0.41Se0.59 and ZnS0.51Se0.49. The SO splitting energy decreases as the Se atomic concentration in the alloy decreases. Two phonon modes (corresponding to ZnS and ZnSe bonds) behavior were observed in the Raman spectra of the ternary alloys. The observed phonon mode frequencies shifted with changes in Se atomic concentration in agreement with theroretical predictions. Gap mode vibration of Se in ZnS lattice was also observed at 221 cm−1 in the ternary sample with small Se atomic concentration (ZnS0.91Se0.09), which also matches closely with theoretically calculated values.

Spectral structure of the X-ray stimulated phosphorescence of monocrystalline ZnSe

This work presents the extensive experimental studies of the X-ray stimulated luminescence, conductivity, phosphorescence and electric current relaxation, and the thermally stimulated luminescence and conductivity of monocrystalline ZnSe. It was found that the luminescence emission band with a maximum at 635nm is a combination of at least three emission bands and that the appropriate recombination centres implement both electronic and hole recombination mechanisms. We propose an energy model of the traps and recombination centres in monocrystalline ZnSe and show that the majority of the generated free electrons and holes recombine in the luminescence centres with an estimated probability of 94.3% and that only a small fraction (5.7%) of generated charge carriers are accumulated in traps during the X-ray excitation of the ZnSe sample.

Synthesis, field emission and optical properties of ZnSe nanobelts, nanorods and nanocones by hydrothermal method

ZnSe nanostructures, such as nanobelts, nanorods and nanocones, were successfully synthesized on Zn foils via a hydrothermal method using EDTA as soft template at low temperature. EDTA played a significant role on the morphology of ZnSe nanomaterials. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) were carried out to characterize the microstructures and chemical compositions of the as-synthesized ZnSe samples. XRD patterns indicated that the as-synthesized ZnSe samples belonged to a cubic zinc blende structure. SEM observation obviously showed that the nanocones had very sharp tips compared to nanorods and nanobelts. The field emission (FE) measurement showed that the as-synthesized ZnSe nanocones had a lower turn-on field of ~1.6Vμm−1 at the current density of 10μAcm−2. A high field enhancement factor of ~4514 was achieved for the ZnSe nanocones. The superior field emission properties were probably attributed to the sharp tips of the ZnSe nanocones. Room temperature photoluminescence (PL) spectroscopy of the ZnSe nanostructures showed a wide band emission from blue light to orange light. The as-prepared ZnSe nanomaterials have promising applications in optoelectronic devices. A possible formation mechanism of ZnSe nanobelts, nanorods and nanocones was also proposed and discussed.

Using nanoindentation and cathodoluminescence to investigate the residual stress of ZnSe

In this study we examined the effects of the nanoindentation-induced residual stress of single-crystalline zinc selenide (ZnSe). We employed the nanoindentation technique to evaluate the dislocation mobility of ZnSe at loading ratios of 10 and 2mN/min, with a holding time of 120s under a constant load. We visualized the resultant dislocation and microcracks using cathodoluminescence (CL) spectroscopy and mapping to compare the nanoindentation-induced residual stresses of the various ZnSe samples. CL mapping revealed massive dislocation activities during the loading process. The dislocations played roles as nonradiative recombination centers that quenched the local CL intensity. Transmission electron microscopy also revealed the effects of nanoindentation-induced residual stress. To obtain insight into the influence of the residual stress and to determine the dislocation mobilities for ZnSe films, it was essential to monitor the quenching effect of nonradiative recombination centers as a function of CL mapping.

Yb-doped ZnSe nanoparticles: synthesis, physical properties and photocatalytic activity.

In this study, Yb-doped ZnSe nanoparticles were synthesized by co-reduction method at 150 degrees C and pH = 12 for 24 h. The obtained materials were characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Powder XRD patterns indicated that the Yb(x)Zn(1-x)Se crystals (x = 0.00-0.10) are isostructural with ZnSe. SEM and TEM images confirmed doping of Yb3+ into the lattice of ZnSe nanoparticles. The UV-Vis diffuse reflectance characteristics of the Yb-doped ZnSe samples were quite similar to that of the undoped sample and showed a strong photoabsorption at visible light range. The electrical conductivity of Yb-doped ZnSe nanomaterials was higher than pure ZnSe at room temperature, and increased with temperature. The photocatalytic activity of synthesized nanoparticles was investigated by the degradation of Orange II solution under visible light irradiation. It was observed that the color removal efficiency of Yb-doped ZnSe catalyst was much higher than that of pure ZnSe (26.28 and 77.10% after 120 min of treatment for ZnSe and Yb(0.06)Zn(0.94)Se, respectively). The results demonstrated the good photocatalytic ability of synthesized nanoparticles under visible light. Also, it was revealed that the decolorization efficiency of Orange II over Yb-doped ZnSe increased with increasing Yb loading up to 6 mol% and then decreased.

Anisotropy in spatial correlations of thermal fields of heated samples of ZnSe

Anisotropy in spatial coherence of thermal fields generated by the heated half-space of ZnSe radiating into a vacuum has been studied and is presented here. The frequency and distance dependencies of the coherence tensors of lateral and normal components of thermal fields are shown. Strong anisotropy in the near field zone is exemplified at different frequencies. It was confirmed that the coherence length within the frequency band of surface polariton excitations depends on the slope of the dispersion curve. The spatial coherence reaches the maximum degree at the initial part of dispersion curve and then is effectively suppressed at the frequency of quasi-static or Coulomb surface polariton. We also demonstrated that the smaller the distance from the surface, the smaller the correlation length of the thermal field up to the delta-correlated fields and their sources within the heated body. In the far zone, the anisotropy in the spatial coherences of components is much smaller than in the near field regime. The traces of the corresponding tensors in the far zone are calculated for the equilibrium and nonequilibrium problems.

Synthesis, structure, optical properties, and band gap tuning of Fe:ZnSe colloidal nanocrystals

Abstract The modification of the band gaps in semiconductor can result in significant enhanced performance, providing new applications for electronic, optoelectronic, and photocatalytic devices. Here we report a facile, cost-effective, and green method to synthesize the Fe:ZnSe nanocrystals with tunable band gap and high emission, and only low cost and environmentally friendly reagents are used, benefiting the practical applications. The synthesized Fe:ZnSe nanocrystal belongs to the zinc blende structure, and the as-synthesized Fe:ZnSe nanocrystal is spherical-shaped and exhibits nearly monodisperse size distribution, as confirmed by the transmission electron microscopy. Effects of different reaction times on the optical properties of the obtained nanocrystals were discussed in detail. Emission properties were controlled at 414–441 nm by tailoring their size, and the blue shift of the absorption edges of Fe:ZnSe samples could be attributed to the quantum confinement within the nanocrystals. More interestingly, the band gap of these as-synthesized nanocrystals can be tuned in the broad range of 3.37–3.10 eV by changing the reaction time. These results show that the new synthetic method of this work provides a new band gap engineering scheme for doped semiconductor nanocrystals and offers the opportunities for the design of ligand-stabilized semiconductor nanocrystals with tunable size and optical properties.

Second-harmonic generation in dry powders: A simple experimental method to determine nonlinear efficiencies under strong light scattering

A simple experimental method for determining the efficiency of second harmonic generation (SHG) using small amounts of dry crystalline powder is described. Contrary to previous techniques, the light scattering effects are explicitly accounted for, and a procedure to eliminate their influence is proposed. The method also permits to assess whether a particular crystal is phase matchable or not. Second-order susceptibility coefficients of eight relevant materials for SHG are determined, and the agreement with the single-crystal data is, in general, fairly good. For polycrystalline ZnSe samples, a situation of the so-called random quasiphase matching is evidenced.

Optical phonons in nanostructured thin films composed by zincblende zinc selenide quantum dots in strong size-quantization regime: Competition between phonon confinement and strain-related effects

Raman scattering in combination with optical spectroscopy and structural studies by X-ray diffraction was employed to investigate the phonon confinement and strain-induced effects in 3D assemblies of variable-size zincblende ZnSe quantum dots close packed in thin film form. Nanostructured thin films were synthesized by colloidal chemical approach, while tuning of the nanocrystal size was enabled by post-deposition thermal annealing treatment. In-depth insights into the factors governing the observed trends of the position and half-width of the 1LO band as a function of the average QD size were gained. The overall shifts in the position of 1LO band were found to result from an intricate compromise between the influence of phonon confinement and lattice strain-induced effects. Both contributions were quantitatively and exactly modeled. Accurate assignments of the bands due to surface optical (SO) modes as well as of the theoretically forbidden transverse optical (TO) modes were provided, on the basis of reliable physical models (such as the dielectric continuum model of Ruppin and Englman). The size-dependence of the ratio of intensities of the TO and LO modes was studied and discussed as well. Relaxation time characterizing the phonon decay processes in as-deposited samples was found to be approximately 0.38ps, while upon post-deposition annealing already at 200°C it increases to about 0.50ps. Both of these values are, however, significantly smaller than those characteristic for a macrocrystalline ZnSe sample.

Physical Properties of Silver Doped ZnSe Thin Films for Photovoltaic Applications

Closed space sublimation (CSS) technique was used to deposit pure (99.99%) zinc selenide(ZnSe) powder on to glass substrates for fabricating the ZnSe thin films. The temperatures of source, substrate and the deposition time were optimized to deposit thin films of different thicknesses. Silver (Ag) was used as a dopant by ion exchange process in the ZnSe thin films. The structural analysis showed that as-deposited ZnSe thin films were polycrystalline having preferred orientation (111) direction. Micro structural parameters such as crystallite size, lattice parameter were determined using X-rays diffraction (XRD). Grains boundaries, roughness on surface and the grain density of the thin film samples were measured by scanning electron and atomic force microscopy before and after Ag doping.As-deposited, Ag-doped ZnSe samples before and after annealing were optically characterized by spectrophotometer in ultra violet, visible and infrared regions. The energy band gap of as-deposited ZnSe thin films for varying thicknesses were ranging from 2.62-2.67 eV which was reduced after Ag doping.The electrical properties showed that as-deposited thin films were highly resistive of the order of 10 -cm and after Ag immersion, it was reduced to 1 -cm. Deposition parameters and Ag doping 8

Liquid Phase Chemical Deposition of High Tech ZnSe Thin Flims

Being a promising and potential candidate for optoelectronic device applications, zinc selenide thin films were obtained for the first time on the glass microslides using a liquid phase chemical bath deposition. The deposition conditions, such as bath temperature (70 0C), deposition time (210 mins.), reaction pH (10.5± 0.2) and quantity of hydrazine hydrate (reducing agent) were finalized and the possible growth mechanism and reaction kinetics have been suggested. As the ZnSe films grow well in strong reducing atmosphere, the quantity of hydrazine hydrate was varied from 2 ml to 15 ml and ZnSe samples were obtained. The final product ZnSe thin films are physically hard, tightly adherent, relatively uniform and diffusely reflecting with light brown colored tinge in smoky appearance. An EDS analysis showed that the film stoichiometry depends on quantity of the added reducing agent in the bath. Structural studies were carried out on these films by an X-ray diffraction technique using Cukα radiation. It appeared that the ZnSe films are hexagonal wurtzite in structure with preferred orientation along <101>. The calculated d-values, intensities of reflections and lattice parameters matched with that of the JCPD data. The calculated particle size decreased with quantity of hydrazine hydrate added in the bath (decrease in Zn/Se ratio). The optical absorption measurements in the range of wavelength from 300-1100 nm showed direct type of transitions with an optical gap decreased from 2.71 eV to 2.60 eV for the change of Zn/Se ratio from 0.993 to 0.571. The surface features revealed by SEM showed that the crystallites are nonuniformly distributed and spherical in shape. From micrographs it is seen that crystallite size decreased with increasing amount of hydrazine hydrate. Some overgrowth like structures (of the same size and shapes) has also been observed at high concentration of hydrazine hydrate.DOI: http://dx.doi.org/10.3126/jncs.v30i0.9384Journal of Nepal Chemical Society Vol. 30, 2012 Page: 130-137 Uploaded date: 12/20/2013

Ligand-assisted fabrication, structure, and luminescence properties of Fe:ZnSe quantum dots

Abstract Here, we report a synthetic route for highly emissive Fe:ZnSe quantum dots in aqueous media using the mercaptoacetic acid ligand as stabilizing agent. The structural, morphological, componential, and optical properties of the resulting quantum dots were explored by the X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and UV–visible absorption spectroscopies. The average crystallite size was calculated to be about ca., 4.0 nm using the Scherrer equation, which correlates well with the value obtained from the transmission electron microscopy analysis. The obtained water-soluble Fe:ZnSe quantum dots in the so-called “quantum confinement regime” are spherical shaped, possess the cubic sphalerite crystal structure, and exhibit tunable luminescence properties. The presence of mercaptoacetic acid on the surface of Fe:ZnSe quantum dots was confirmed by the Fourier transform infrared spectroscopy measurements. As the ligand/Zn molar ratio increases from 1.3 to 2.8, there is little shift in the absorption peak of the Fe:ZnSe sample, indicating that the particle size of the obtained quantum dots is not changed during the synthetic process. The photoluminescence quantum yield of the as-prepared water-soluble Fe:ZnSe quantum dots can be up to 39%. The molar ratio of ligand-to-Zn plays a crucial role in determining the final luminescence properties of the resulting quantum dots, and the maximum PL intensity appears as the ligand-to-Zn molar ratio is 2.2. In addition, the underlying mechanism for the resulting tunable luminescence properties of the obtained Fe:ZnSe quantum dots was also elucidated.

Synthesis and characterization of ZnSe rose-like nanoflowers and microspheres by the hydrothermal method

ZnSe rose-like nanoflowers and microspheres were successfully grown on Zn foils by the hydrothermal method at 220°C for 36h. Scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) spectroscopy were used to observe the morphologies, structures, chemical compositions and optical properties of the as-synthesized ZnSe samples. The XRD patterns revealed that as-synthesized ZnSe nanoflowers and microspheres have cubic zinc blende structure. The SEM observations showed that low concentration of EDTA was beneficial to obtain the ZnSe rose-like nanoflowers. With increase of EDTA concentration, the morphology of the as-synthesized samples transformed into microspheres. It was proved that EDTA played a significant role during the synthesis of ZnSe rose-like nanoflowers and microspheres. Room temperature photoluminescence (PL) spectroscopy of the samples showed that the spectra were wide band from blue light to orange light. Furthermore, a possible formation mechanism of ZnSe nanoflowers and microspheres was proposed and discussed.

Fabrication and power scaling of a 17 W Cr:ZnSe waveguide laser

We report the fabrication and operation of a Cr:ZnSe buried channel waveguide laser operating at 2500 nm with a linewidth of 10 nm and a maximum power output of 1.7 W. Ultrafast laser inscription is used to fabricate the depressed cladding waveguide in a polycrystalline Cr:ZnSe sample. A thermal model is developed and predicts performance degradation at higher pump levels due to thermal quenching of the lifetime. This prediction is supported by the experimental results.

Efficient mid-infrared Cr:ZnSe channel waveguide laser operating at 2486 nm

We report a Cr:ZnSe channel waveguide laser operating at 2486nm. A maximum power output of 285mW is achieved and slope efficiencies as high as 45% are demonstrated. Ultrafast laser inscription is used to fabricate the depressed cladding waveguide in a polycrystalline Cr:ZnSe sample. Waveguide structures are proposed as a compact and robust solution to the thermal lensing problem that has so far limited power scaling of transition metal doped II-VI lasers.

Passively Q-switched diode-pumped Er:YAG solid-state laser

We demonstrated laser operation of a passively Q-switched diode-pumped Er:YAG solid-state laser emitting at 1645 or 1617 nm depending on the initial transmission of the Cr:ZnSe saturable absorber. The crystal emitted up to 10 W at 1645 nm and up to 8 W at 1617 nm in CW mode while pumped with 65 W of incident pump power at 1533 nm. In passive Q-switched mode with 40 W of incident power, a Cr:ZnSe saturable absorber with initial transmission of 85% led to 330 μJ pulse energy, 61 ns pulse duration at a repetition rate of 1460 Hz at 1645 nm. An 80% initial transmission Cr:ZnSe sample led to 510 μJ energy pulses, 41 ns pulse duration at a repetition rate of 820 Hz with a central wavelength change from 1645 to 1617 nm. This is the first reported passively Q-switched diode-pumped Er:YAG laser operating on the (4)I(13/2)→(4)I(15/2) transition.

Ion-exchange synthesis and enhanced visible-light photocatalytic activities of CuSe-ZnSe flower-like nanocomposites

CuSe-ZnSe flower-like nanocomposites with uniform diameters can be easily fabricated on a large scale by a controlled ion-exchange reaction between monodisperse ZnSe flower-like nanostructures and Cu2+ ions in solution. The difference of solubility products (Ksp) of ZnSe and CuSe is the main driving force for the formation of these flower-like nanocomposites. The Cu content greatly influences the physical properties and photocatalytic activity of obtained CuSe-ZnSe nanocomposites. The as-produced CuSe-ZnSe nanocomposites show tremendous enhancements on the photocatalytic degradation ratio of organic dyes methylene orange (MO) and methylene blue (MB) under visible-light irradiation. The 8wt.% CuSe-ZnSe sample exhibits the highest degradation ratio for both MO (ca. 100%, 90min) and MB (ca. 96%, 60min), which are over 4 times and 2.5 times than that of the pure ZnSe sample, respectively. Based on the data of UV–vis diffuse reflection spectra, XPS and PL spectra, the enhancements of photocatalytic activities of CuSe-ZnSe flower-like nanocomposites are due to the effective separation of photo-electrons and holes induces by the direct initiates interfacial charge transfer (IFCT) from the valence band (VB) of ZnSe to CuSe, which results in the reduction of CuSe to Cu2Se. This work not only highlights the potential use of visible-light-driven CuSe-ZnSe flower-like nanocomposites photocatalysts, but also emphasizes the simple ion-exchange in situ growth method for the preparation of selenides heterogeneous structures.

Hydrothermal synthesis and characterization of Nd-doped ZnSe nanoparticles with enhanced visible light photocatalytic activity

In the present study, Nd3+-doped ZnSe nanoparticles with variable Nd contents were successfully synthesized via a hydrothermal process using Neodymium (III) chloride hexahydrate as the doping source. X-ray diffraction, UV–Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy and transmission electron microscopy were used for characterization of the synthesized nanoparticles. It was confirmed by the DRS analysis that both of the undoped and Nd-doped ZnSe samples had significant optical absorption in the visible light range. The photocatalytic performance of as-synthesized nanoparticles was investigated towards the decolorization of C. I. Acid Orange 7 solution under visible light irradiation. Results indicated that the loading of Nd dopant into ZnSe nanoparticles significantly enhanced the photocatalytic activity of pure ZnSe with increasing Nd loading up to 6 mol% (color removal efficiency of 24.31 % for ZnSe and 84.20 % for Nd0.06Zn0.94Se after 120 min of treatment) and then the photocatalytic activity began to decrease.

Femtosecond SESAM-modelocked Cr:ZnS laser

We report self-starting femtosecond operation of a 180-MHz SESAM-controlled prismless Cr:ZnS laser around 2400 nm at open air and room temperature. Dispersion compensation was achieved by a combination of bulk materials and chirped mirrors. Both soliton- and chirped-pulse operation regimes have been demonstrated with 130 fs (630 fs) pulse duration at 130 (205) mW average output power, respectively. The output power was about 30% higher than for a comparable Cr:ZnSe sample in the same cavity.