Papers by Keyword: ZnSe

Abstract: In this research, Zn_1-xCd_xSe alloys (x from 0 to 1) were synthesized by solid-state microwave (SSM) method of producing thermally evaporated thin films. The cubic structure and the elemental ratios of the films were studied using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The optical characterizations of the as-deposited film in terms of the energy band gap (Eg), photoluminescence (PL), and Raman shift spectra were conducted at the room temperature. The Eg values for the thin films from ZnSe to CdSe were 3.4 to 1.7 eV, respectively. The PL orange emission for ZnSe thin film at 565 nm, whereas 590 nm in the yellow region for CdSe thin film. From Raman shift spectra, the two longitudinal-optical phonon modes (1LO and 2LO) at 240, and 490 cm^-1 are assigned for the ZnSe and CdSe thin films.

Abstract: Zinc oxide (ZnO) nanorods is widely investigated due to its high photoelectrochemical conversion performance. Further enhancement may be afforded by introducing a metal chalcogenide sensitization layer such as zinc selenide (ZnSe). In this study, ZnO nanorods were electrodeposited with ZnSe at potential range from -0.5 V to -0.9 V vs Ag/AgCl reference electrode. Structural, morphological and optical properties of ZnSe electrodeposited were investigated as a function applied potential by using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis). ZnSe electrodeposited for 15 minutes at -0.7 V showed crystallite size of 20.13 nm with the lowest band gap energy of 2.97 eV. The existence of ZnSe particles with the size of 41.8 nm were proven by FESEM images, after ZnSe particles were electrodeposited onto ZnO nanorods that have an average diameter of 62.6 nm and length of 1.6 µm. The photocurrent density generated by samples were measured in a three-electrodes cell incorporated with halogen lamp. The photocurrent generated increased between -0.5 V to -0.7 V before dropped at higher applied potential due to hydrogen evolution process which affected the thin film quality, ultimately affecting photoconversion performance. The highest photocurrent density of 0.2621 mAcm^-2 was recorded for samples prepared at -0.7 V vs Ag/AgCl.

Abstract: Following successful growth of zinc oxide (ZnO) nanorods, a layer of zinc selenide (ZnSe) was electrodeposited onto the nanorods to further enhance its conversion efficiency in the photoelectrochemical (PEC) cell. The electrodeposited ZnSe layer onto the ZnO nanorods was subjected to heat treatment at 200, 250 and 300°C. The prepared films were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis) to investigate the structural, morphological and compositional characteristics. Additionally, PEC conversion generated by the prepared thin films were tested with photocurrent measurements under calibrated visible illumination from a halogen lamp. Based on FESEM analysis, the thickness of ZnO thin film increased with temperature. However, the diameters of the ZnO nanorods were found to be in a decreasing trend upon heat treatment at higher temperature. The electrodeposited ZnSe layer at the potential of -0.7 V for 60 seconds (calcined at 200°C) possessed crystallite size of 20.1 nm. According to UV-Vis analysis, band gap energy measured was 2.8 eV, which is very close to standard ZnSe band gap value (2.7 eV). Additional layer of ZnSe electrodeposited enhanced thin film performance in terms of current density as much as 37.4% while having high photocurrent density of 0.2671 mAcm^-2.

Abstract: ZnSe quantum dots (QDs) with high intrinsic fluorescence quantum efficiency (QY) and low defect luminescence were prepared by hydrothermal method assisted with ammonia, in which the selenium powder and zinc acetate were used as Se and Zn source, and the mercaptopropionic acid (MPA) was used as ligand. Effect of ammonia amount, Zn/Se ratio, Zn/MPA ratio, and reaction time was investigated in detail in this study. The as-prepared ZnSe QDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption spectrum (UV-Vis), fluorescence spectrum (PL). ZnSe QDs assisted with ammonia were sphalerite, and with emission peak in the range of 380~405nm. The optimal condition was following: Zn/Se ratio was 5, Zn/MPA ration was 0.25, reaction temperature was 110 °C and reaction time was 6 h. Under the optimal condition, ZnSe QDs with intrinsic emission QY of 47% and diameter of 3.8±0.3 nm can be obtained. The ZnSe QDs prepared in this study were expected to replace toxic Cd-related QDs in biomarkers, violet and blue light solid luminescent devices, and provide excellent parent materials for the doped ZnSe QDs system.

Abstract: Zinc selenide (ZnSe) nanowires were grown on Si and fused quartz substrates by a simple vapor transport method of heating the ZnSe powder at 1100 °C in a tube of the furnace. The obtained yellow colored product has indicated to be the high density of ZnSe nanowires with diameters ranging from 50 to 200 nm. Low-temperature photoluminescence spectra for ZnSe nanowires show near band-edge emissions. The free excitonic emissions were observed at ~2.8 eV.

Abstract: The physical and chemical characterize of quantum dots (QDs) extensively depend upon the optical and morphological factors such as size and shape. The zinc selenide (ZnSe) quantum dots (QDs) have been prepared by chemical method and used to fabricate quantum dot hybrid junction devices with different types of organics polymers. The optical studies illustrate that the band gap value from the photoluminescence (PL) with high intensity of these QDs is found about 3.1 eV. The electroluminescence's (EL) hybrid devices were demonstrated by room temperature PL and electroluminescence (EL). Current-voltage (I–V) characteristics indicate that the output current is good compared to the few voltages (5.5 V) used which gives good results to get a generation of white light. The EL spectrum reveals a broad emission band covering the range from 350 - 700 nm. The emissions producing this white luminescence were recognized depending on the chromaticity coordinates (CIE 1931). The correlated color temperature (CCT) was found to be about 5759, 3500 and 3498 K for ITO/TPD/ZnSe, ITO/PPV/ZnSe and ITO/PEDOT/ZnSe QDs respectively. Fabrication of EL- hybrid devices from semiconductors materials (ZnSe QDs) with holes injection organic polymer (TPD, PPV and PEDOT) was effective in white light generation.

Abstract: The white light generation mechanism was explained depending on mixing colors from the illuminated CdTe/ZnSe core/shell nanocrystals. The color mixed in CdTe/ZnSe core/shell system were used to generate intense white light when illuminated by InGaN/GaN UV LED (λ=360 nm) the core/shell system tuned the chromaticity coordinates to (0.30, 0.32) and increased the intensity of the emitted white light. This improvement was attributed to the overlap of emission with the photoluminescence (PL) spectrum of CdTe/ZnSe core/shell which leads to a cold white light generation.

Abstract: A novel one pot synthesis approach in oleic acid medium was employed to obtain monophasic ZnSe quantum dots (QD) of average size 3.7nm. The QDs were well crystalline in hexagonal phase as revealed by x-ray diffraction and high resolution transmission electron microscopy (HRTEM) studies. The ZnSe QDs exhibit sharp emission peak in the blue (465nm) with 385picosecond fluorescence decay time. The theoretical band gap corresponding to 3.7nm ZnSe QDs matched well with the measured 3.11eV band gap of synthesized QDs which thus showed quantum confinement effect.

Abstract: ZnSe thin films were deposited onto glass substrates by CW-CO₂ laser evaporation with the various evaporation times and laser power. SEM studies showed that the thicknesses of deposited films were varied from 176 nm to 1824 nm. AFM studies showed that the surface roughnesses were varied from 2.4 nm to 5.1 nm. The structure of deposited films were indicated by XRD technique which the result showed the cubic structure. The average crystallite sizes were calculated from the XRD pattern with ranged between 23.8 nm and 31.7 nm. The transmission spectates were ranged from 250 nm to 900 nm. The values of the optical bandgap energies determined from the absorption spectra were ranged between 2.61 eV and 2.88 eV. This paper presents the simple and low cost technique for ZnSe film deposition. Another advantage of this research is the high-precision control of thickness by the variation of the evaporation time and laser power.

Abstract: With ammonia and hydrazine hydrate as complexing agents, ZnSe has been deposited as the buffer-window layer of solar cells from chemical solution, in which the complexion played vital role in controlling the film growth. We calculated various complexion in chemical solution deposited ZnSe precursor with solubility theory. And the main complexion and their concentration with adding of complexing agents and pH value have been investigated. And we found that the main complexion are Zn (NH₃)₃²⁺ and Zn (NH₃)₄²⁺, the concentration of which varied with the adding of ammonia and pH value.