Optical Properties Of ZnSe Research Articles

STRUCTURAL, ELECTRONIC, AND OPTICAL PROPERTIES INVESTIGATION OF ZnSe CUBIC SPHALERITE COMPOUNDS USING DENSITY FUNCTIONAL THEORY (DFT)

Theoretical investigation of the structural, elastic, electronic and optical properties of ZnSe using the plane-wave pseudo potential formalism method of density functional theory with local density approximation (LDA) and generalized gradient approximation (GGA) as exchange-correlation potentials (DFT). The optimal structure of the binary semiconductor ZnSe crystallized in the complex phase of sphalerite was determined by studying the energy as a function of the basic unit volume. The calculated equilibrium lattice constants, bulk moduli and volumes are in reasonable agreement with the available experimental results. The electronic and chemical bonding properties were investigated by calculating the band structure, density of states and Mulliken population. We found that for ZnSe, the band gap of LDA is 1.33 eV and that of GGA is 1.34 eV. In addition, optical properties (absorption coefficients) were calculated.

Optical properties of ZnSe using linear response theory

The electronic structure and optical response of ZnSe are studied in this work. The studies are carried out using first-principles full-potential linearized augmented plane wave method. After settling the crystal structure, the electronic band structure of the ground state of ZnSe is calculated. Linear response theory is applied to study optical response considering bootstrap (BS) and the long range contribution (LRC) kernels for the first time. We also use the random phase and adiabatic local density approximations for comparison. A procedure based on empirical pseudopotential method is developed to find material dependent parameter α required in the LRC kernel. The results are assessed by calculating the real and imaginary parts of linear dielectric function, refractive index, reflectivity, and the absorption coefficient. Results are compared with other calculations and available experimental data. The results of LRC kernel finding α from the proposed scheme are encouraging and at par with the BS kernel.

Electronic and optical properties of ZnSe by theoretical simulation TB-mBJ (Tran-Blaha modified Becke Johnson) associated to analysis techniques XPS (X-Ray Photoelectron Spectroscopy); REELS (Reflective Electron Energy Loss Spectroscopy) and PLS (Photoluminescence Spectroscopy)

Our work aims to establish a correspondence between the obtained theoretical and experimental results on the electronic and optical properties of ZnSe.The calculated DOS (Density of States) using the FP-LAPW method with the Tran-Blaha modified Becke-Johnson exchange-correlation potential reveal that the upper valence energy levels involve an important contribution from the Se-(4p and 3d) electron states with a small contribution from the Zn-2s states.The real (ε1(ω)) and imaginary (ε2(ω)) parts of the dielectric function show the anisotropy character of w-ZnSe.The main peaks appearing in the ε2(ω) spectrum, are calculated by summing over all contributions of electronic transitions between the pairs of bands Vn→Cn′, where Vn is an occupied valence band and Cn′ is an unoccupied conduction band. Experimentally, the XPS (X-Ray Photoelectron Spectroscopy) analysis technique is used to show the clean and homogeneous state of ZnSe. To confirm the calculated electron transitions, we use the REELS (Reflected Electron Energy Loss Spectroscopy) technique of great sensitivity for displaying the electron interband transitions. The electron states in the w-ZnSe gap are determined through the Gaussian deconvolution of the photoluminescence spectrum (PLS).

Green synthesis and optical properties of ZnSe:Cu@ZnS core/shell nanocrystals fabricated by new photochemical microwave-assisted colloidal method

Abstract Growth of a secondary material-shell on a core of another material and so, formation of a core-shell system has been a successful route in the surface modification of nanostructured samples. In this research, ZnSe:Cu and ZnSe:Cu@ZnS core-shell nanocrystals (NCs) with different contents of Cu-dopant under microwave irradiation times (MWIRTs) = 0 & 6 min were synthesized by a new and rapid photochemical microwave-assisted method at home temperature. Crystal structure, crystallite size (by XRD analysis), morphology and elemental analysis (by TEM, FESEM, EDX and Map), strain, dislocation density, absorption edge, energy band gap (by exact method of DASF), the exact nature of charge carrier optical transition (m), Urbach energy ( E tail ), Refractive index (n), dielectric constant (e) at the absorption edge and third order non-linear optical susceptibility (χ(3)) were determined. The influences of various experimental variables, including formation of ZnS shell on ZnSe:Cu core, Cu content and MWIRT on their opto-structural features were systematically investigated. The obtained NCs present high degree of crystallinity and have a cubic zinc blende structure which their diameters varies from 1.81 to 2.26 nm. The formation of core-shell structures was confirmed TEM. For ZnSe:Cu@ZnS core-shell NCs, XRD diffraction peaks shifted slightly to higher angles. Band gap of ZnSe NCs was obtained about 3.45 eV, which was tunable by formation of ZnS shell on ZnSe:Cu NCs core and also by altering the synthesis conditions. However, the band gap values of ZnSe:Cu@ZnS systems were generally smaller than that of ZnSe:Cu NCs; also, in each cases of bare ZnSe:Cu NCs and ZnSe:Cu@ZnScore/shell NCs, increase in MWIRT results to the red shift in band gap. For all samples, optical charge carrier transition index of m were found to be nearly around 3/2 (correspond to the direct non-allowed transition gap type), except for ZnSe:Cu(1.5%)@ZnS with MWIRT = 6 min with m-index nearly around 1/2 (correspond to the direct allowed transition gap type); the recent exception may be due to its different structure, which has been caused to its different structure certified by TEM. Upon the all opto-structural performed analysis, ZnSe:Cu(0.75%)@ZnS and ZnSe:Cu(0.1%)@ZnS NCs synthesized photochemically under MWIR = 6 min, have the highest (χ(3)), lowest band gap and lowest lattice suggesting them as promising and potentially materials in nano-optoelectronic applications such as solar cells, fibers or even in strong coating materials.

Luminescent ZnSe:Mn/ZnS@PMMA nanocomposites with improved refractive index and transparency

This paper deals with development of a novel ZnSe:Mn/ZnS@PMMA nanocomposites fabricated via simple film casting methods using commercial available PMMA resin (DEGALAN® Evonik). Hydrophobic ZnSe:Mn/ZnS nanoparticles were successfully produced by the hot-injection method using high boiling point organic solvents. ZnSe:Mn colloidal nanoparticles were protected from luminescence quenching and degradation by overcoating with a ZnS shell. The coverage of the nanoparticles with three layers of the ZnS shell effectively protected them against photooxidation and quenching in organic solvents. The crucial step in the production of highly transparent and luminescent ZnSe:Mn/ZnS@PMMA polymer nanocomposites was the purification of the ZnSe:Mn/ZnS nanoparticles from by-products and unreacted precursors. The optical properties of ZnSe:Mn/ZnS@PMMA nanocomposites were characterized by UV–Vis and spectroscopic ellipsometry measurements. All nanocomposite films demonstrated high transmittance in the visible range (70–90%), an intense orange emission originating from homogeneously dispersed ZnSe:Mn/ZnS nanoparticles. The intensity of the orange emission increased with increasing ZnSe:Mn/ZnS nanoparticle concentration in the nanocomposite up to a quantum yield (QY) of 19% ± 5 for a nanocomposite with nanoparticles content up to 7% wt. These novel polymer nanocomposites exhibited good optical properties (high refractive index of 1.59 at 450 nm) and stability under ambient conditions and can be easily deposited over large areas by printing process.

Effects of substrate temperature on microstructure, morphology and optical properties of ZnSe:Co films obtained by pulsed laser deposition

ZnSe:Co thin films were grown on sapphire (Al2O3) substrates by pulsed laser deposition at different substrate temperature. Evolutions of the microstructure, morphology and optical properties of the ZnSe:Co thin films as a function of substrate temperature were analyzed. The results indicated that the crystalline quality was promoted and the films demonstrated increasing (111) preferred orientation with increasing substrate temperature. Excellent crystalline quality and (111) preferred oriented thin film was grown at substrate temperature of 800 °C. The refractive index and dielectric constant analyzed by the transmission spectra increased with elevating substrate temperature, which may be due to the promotion of the film packing density. The thin films with wider optical band gap in range of 2.73 eV to 3.27 eV were obtained in the experiment. The band gap decreased when the substrate temperature was increased from 25 °C to 600 °C, and then increased with a further increase of substrate temperature to 800 °C. The evolution of band gap associates with the quantum confinement effect.

The Effect of Surface Defects on the Optical Properties of ZnSe:Eu Quantum Dots

The Effect of Surface Defects on the Optical Properties of ZnSe:Eu Quantum Dots

Optical properties of ZnSe(Te) with ytterbium impurity.

We report the results on infrared transmission measurements of non-doped and tellurium-doped crystals of zinc selenide grown from the melt. It was found that non-doped samples feature high transmission (50%-60%) for the wavelengths of 1-22μm. The efficient scintillating crystals of ZnSe(Te) are almost opaque for λ>7 μm. Doping these samples with ytterbium from the gas phase does not achieve any significant transmission increase for non-doped ZnSe samples in the spectral range of 1-22μm. However, it considerably increases (up to 50%) transmission for doped ZnSe(Te) at the wavelengths λ>10 μm. These optical peculiarities were analyzed taking into account restructurization of point defect ensembles created by Te and Yb impurities.

Formation and optical properties of ZnSe and ZnS nanocrystals in glasses

ZnSe and ZnS nanocrystals (NCs) were precipitated in glasses through heat-treatment. High resolution transmission electron microscope image confirmed that ZnSe NCs were formed in the silicate glasses, and the X-ray diffraction patterns confirmed that ZnS NCs were precipitated in the borosilicate glasses. Absorption shoulders of the ZnSe NCs and ZnS NCs appeared at ~2.76eV and ~3.78eV, corresponding to the bandgap energies of bulk ZnSe and ZnS crystals, respectively. Instead of the intrinsic emissions, broad-band visible photoluminescence from the surface defects or color centers in the glasses was observed from these ZnSe or ZnS NCs.

Effect of thermal annealing on the physical properties of Zn1−x Cu x Se thin films deposited by close spaced sublimation technique

Thin films of Zn1−x Cu x Se (x= 0.00, 0.05, 0.10, 0.15, 0.20) were grown on glass substrates by closed space sublimation technique. The deposited films were annealed at 200 °C and 400 °C in air for 1 h. The annealed samples have been investigated through Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), spectroscopic ellipsometer, spectrophotometer and Raman spectroscopy. Through RBS, the composition of the films was calculated and compared with the initial concentration. Structural characterization including crystal structure, crystal orientation, lattice parameter, grain size, strain and dislocation density were carried out using XRD data. From XRD spectra it was revealed that the as-deposited and annealed films were polycrystalline in nature with zinc-blende structure. However, the crystallinity and the grain size were improved with the increase of annealing temperature. According to Raman spectroscopy, it was observed that as deposited and annealed samples have the same characteristic vibrational modes of ZnSe at low and high frequency optical phonon modes while another mode was observed for 400 °C annealed samples at 745 cm−1. Spectroscopic ellipsometer has been used to found annealing effect on the optical properties of ZnSe. The band gap energy has been determined using transmission spectra. It was found that the band gap energy of the film increased with the increase of annealing temperature.

Studies on structural and optical properties of ZnSe and ZnSSe single crystals grown by CVT method

The ZnSe and ZnSSe single crystals have been grown by chemical vapour transport (CVT) with iodine as a transporting agent. The source and growth temperatures of the reactor are maintained at 850°C and 900°C respectively using the two zone horizontal resistive heating furnace. The grown crystals are characterised by structural, surface morphological and optical properties. The XRD pattern shows that the peaks due to reflection from (111), (220) and (311) planes belong to the cubic zinc-blend structure. The composition of grown ZnSe crystal has been determined by EDXRF analysis as Zn (52.5%) and Se (47.5%). The XPS study of grown ZnSe single crystal has been studied. The HRSEM images reveal the step, spiral and triangular patterns. The optical absorption study reveals the absorption cut off wavelength as 483nm (2.57eV) for ZnSe and 441nm (2.81eV) for ZnSSe crystals. The photoluminescence studies reveal the band edge emission and defect level emissions of ZnSe and ZnSSe single crystals.

Optical control of the spindle-liked ZnSe quantum dots with precursor solvent and Mn doping

Spindle-liked ZnSe and Mn:ZnSe quantum dots (QDs) were formed via an optimized greener approach, which may be attributed to the amine ligands adhering asymmetrically to the crystal facets. Powder X-ray diffraction (XRD) patterns revealed that the ZnSe and Mn:ZnSe QDs have a zinc blende cubic crystal structure. The crystallite size of ZnSe was calculated to be about 4nm from the (111) peak width using the Scherrer equation, which was in agreement with the HRTEM findings. The fluorescence emission peak of as-prepared ZnSe and Mn:ZnSe QDs was 431nm and 580nm respectively. We investigated the effect of the reaction temperature, reflux time, precursor solvent, size of MnSe core and overcoating temperature of ZnSe layer on the optical properties of ZnSe and Mn:ZnSe QDs. It is shown that the precursor solvent plays a key role in the formation of the magic-sized QDs (MSQDs). And as a result, doped quantum dots (d-dots) showed a large Stokes shift and enhanced photoluminescence, and smaller size of the MnSe core and suitable overcoating temperature of ZnSe shell were identified as two key parameters for obtaining the high quality d-dots.

Influence of annealing medium on photoluminescence and optical properties of ZnSe:Cr crystals

Modification of photoluminescence (PL) and optical properties of ZnSe:Cr crystals caused by annealing in medium of Zn or Se vapors are investigated. Possibility to modify the intensity of infrared (IR) impurity PL (∼1µm and 2µm) and optical absorption spectra by several orders of magnitude, reversibility of the observed modifications of crystal properties, influence of co-doping with Cr and Cl impurities on radiative and optical properties of ZnSe are discussed. Models that explain both disappearance of CrZn2+ centers responsible for the IR emission due to crystal enrichment with Zn and formation of Cr2Se3 precipitates against the background of crystal enrichment with Se are suggested. Complex PL bands in the IR and edge spectral ranges are analyzed for ZnSe:Cr crystals.

ZnSe∶Cu/CdS核壳量子点的合成及光学性能研究

Water-soluble ZnSe:Cu quantum dots were synthesised in aqueous solution,ZnSe:Cu/CdS core/shell quantum dots(QDs)with different shell thickness were obtained in this paper.The influence of shell thickness on the optical properties of ZnSe:Cu QDs was studied.The samples were characterized by TEM,XRD,PL and UV-Vis.The results showed that ZnSe:Cu/CdS core/shell QDs have a cubic zinc-blende structure and are spherical with good dispersibility.The average grain size increased from 2.7 to 4.0 nm after the shell modification.The redshift of core/shell QDs compared with the core QDs was observed in both the UV-Vis and the PL spectra,which suggested that the size of core/shell QDs increased.The results proved that CdS shell were coated on the surface of ZnSe:Cu QDs and formed the ZnSe:Cu/CdS core/shell structure QDs.The PL intensity of the ZnSe:Cu QDs decreased with higher stability after being coated by CdS shell.

Water-Based Route to Colloidal Mn-Doped ZnSe and Core/Shell ZnSe/ZnS Quantum Dots

Relatively monodisperse and highly luminescent Mn(2+)-doped zinc blende ZnSe nanocrystals were synthesized in aqueous solution at 100 °C using the nucleation-doping strategy. The effects of the experimental conditions and of the ligand on the synthesis of nanocrystals were investigated systematically. It was found that there were significant effects of molar ratio of precursors and heating time on the optical properties of ZnSe:Mn nanocrystals. Using 3-mercaptopropionic acid as capping ligand afforded 3.1 nm wide ZnSe:Mn quantum dots (QDs) with very low surface defect density and which exhibited the Mn(2+)-related orange luminescence. The post-preparative introduction of a ZnS shell at the surface of the Mn(2+)-doped ZnSe QDs improved their photoluminescence properties, resulting in stronger emission. A 2.5-fold increase in photoluminescence quantum yield (from 3.5 to 9%) and of Mn(2+) ion emission lifetime (from 0.62 to 1.39 ms) have been observed after surface passivation. The size and the structure of these QDs were also corroborated by using transmission electron microscopy, energy dispersive spectroscopy, and X-ray powder diffraction.

Controlled Synthesis and Characterization of ZnSe Quantum Dots

Adopting improved metal-organic "Green method," Colloidal ZnSe quantum dots were synthesized by using cheap and low toxic zinc oxide (ZnO) in an organic solvent system of 1-hexadecylamine (HDA), lauric acid (LA) and tri-n-octylphosphine (TOP). The effects of HDA dosage, injection temperature, growth temperature and time on the microstructure and optical properties of ZnSe were studied by means of X-Ray diffraction(XRD), transmission electron microscopy (TEM), spectrofluorometers and ultraviolet spectrophotometer, respectively. The results showed that ZnSe quantum dots with the best range of the size evolution were obtained under the condition of injection at 280 degrees C and growth at 240 degrees C by choosing the optimal parameters of ZnO:HDA:LA= 1:2.1:5.2 and TOPSe = 1 mol/L. Its size became larger and the emission peak shifted obviously to red with increasing the growth time. Meanwhile, the obtained ZnSe was of the wurtzite structure, had good uniformity and fluorescent characteristics.

Luminescence of Cu<sup>2+</sup>-Doped ZnSe Quantum Dots with Different Parameters

Cu2+-doped ZnSe quantum dots (ZnSe:Cu2+ QDs) are synthesized in aqueous solution via a co-precipitation method with thioglycolic acid (TGA) as a stabilizer. Green emission is observed under 365 nm UV excitation. X-ray diffraction patterns and transmission electron microscopy image show that ZnSe:Cu2+ QDs are sphalerite cubic structure, similar to round in shape, the average diameter is 6 nm. The concentration of Cu2+ ions and TGA, pH, reaction time and aging time have influences on optical properties of ZnSe:Cu2+ QDs. The luminescence of as-prepared products with different parameters is characterized using fluorescence spectrophotometer. The high fluorescence intensity has been got when the concentration of Cu2+ ions is 4.0% (molar ratio), TGA is 83.4 μl (mol ratio Zn: TGA=1:2), pH is 9.5, reaction time is 2h. The luminous intensity increases with the extension of aging time.

Preparation and optical properties of ZnSe:Ni crystals

The ZnSe:Ni single crystals doped by diffusion are investigated. The diffusion is carried out from metallic nickel in helium and argon atmosphere. The optical-density spectra are investigated in the wave-length range of 0.4–3 μm. From the value of the absorption-edge shift, the nickel concentration in crystals under investigation is determined. The optical-density and luminescence spectra of ZnSe:Ni are identified. The nickel-impurity diffusion profile is determined by measuring the relative optical density of crystals in the visible spectral region. The diffusivities of nickel in ZnSe crystals are calculated at temperatures of 1073–1273 K.

Calculation of electronic and optical properties of Zn-based II–VI semiconductors

ZnSe and ZnS are the prototype II–VI semiconductors and their cubic phase, which occurs naturally as a mineral, has been called the zinc-blende structure. ZnSe has received particular attention as a blue-lasing material and tremendous experimental efforts have been made to fabricate a sustainable ZnSe blue laser. On the other hand, the ternary system ZnSxSe1−x is a good candidate for developing optoelectronic devices such as light emitting diodes (LEDs) or semiconductor lasers. It is also used as waveguides and confinement layers in laser diodes (LDs).In the present study, we have computed the electronic and optical properties of ZnSe, ZnS and ZnSxSe1−x using the local model pseudopotential method under the VCA. A central aim of this study is to present the electronic and optical properties of the materials of interest in the zinc-blende structure.

Optical properties of ZnSe on GaN (0 0 0 1) grown by MBE

We have grown ZnSe on GaN (0 0 0 1) substrate by MBE. Although the X-ray rocking curve shows that the growth axis of ZnSe is 〈1 1 1〉, the samples show only ZnSe-LO Raman signal in the optical arrangement of back-scattering geometry. The photoluminescence (PL) profiles indicate a strong self-activated emission band around 2.1–2.2 eV due to the Zn vacancies. Some structures observed in the PL spectra are due to the resonant Raman scattering corresponding to the LO phonon replica. The PL peaks at 2.85, 2.82 and 2.79 eV are considered to be the Raman signals of 7-, 8- and 9-LO, respectively, from the laser diode 3.06 eV (405 nm) used as the excitation source.