Preparation of ZnSe-ZnS alloy quantum dots by a hydrothermal method and their optical properties
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Abstract We prepared colloidal ZnSe x S 1− x alloy quantum dots (QDs) and investigated their optical properties. ZnSe x S 1− x QDs were successfully prepared by a hydrothermal method, which was confirmed by the results of X-ray structural analysis. When the alloy composition was decreased from x = 1 to 0, the absorption energy continuously shifted to the high energy side. Band-edge photoluminescence (PL) was the main PL band in ZnSe QDs, whereas only defect - related PL band was observed in ZnS QDs. The band-edge PL was clearly observed as the main PL band for x = 0.52 to 1, which shifted to the high energy side by decreasing x .Keywords:
Absorption edge
This chapter contains sections titled: Introduction Synthesis of CdSe Quantum Dots Bandgap Structure and Photoluminescence of CdSe Quantum Dots Photoluminescence Spectral Shifts Enhancement of Photoluminescence in CdSe Quantum Dots On and Off Luminescence Blinking in Single Quantum Dots Conclusions References
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The optical properties of TiO 2 are changed while doped with impurity atoms. This paper made a systematical calculation of the bandgap, the density-of-states (DOS), the optical properties for pure TiO 2 , and Bi-doped anatase TiO 2 according to the first-principles plane wave ultrasoft pseudopotential method which is primarily based on the density functional theory (DFT). The calculation results exhibit that the bandgap decreased after doping, and the impurity energy level is produced into the bandgap of Bi-doped TiO 2 , which makes red-shift for the absorption band edge of Bi-doped TiO 2 and the absorption is enhanced more in the visible light range.
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Photoluminescence excitation
Porous Silicon
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In this work, we present a detailed investigation of the low temperature emission properties of ZnSeO alloys by means of photoluminescence, micro-photoluminescence, and time-resolved photoluminescence. We show that the low temperature broad photoluminescence spectrum of ZnSeO attributed to the recombination of localized excitons is composed of sharp lines related to individual trapping states. Based on studies of photoluminescence thermal quenching from individual trapping states and photoluminescence dynamics, the mechanism of nonradiative recombination in ZnSeO alloys is discussed. Moreover, an unexpected decrease of the low temperature Stokes shift with increasing oxygen content is observed in contrast to what has been reported for GaAs based highly mismatched alloys. The possible origin of this effect is proposed.
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We examined the change in photoluminescence spectra of porous Si when it is oxidized then deoxidized chemically. After both steps, photoluminescence shifted to higher frequencies and increased in intensity. These shifts to higher frequencies indicate the photoluminescence is a result of the quantum size effect. Moreover, the increase in photoluminescence intensity after oxidation suggests that termination by hydrogen on the porous Si surface does not always play a key role in the photoluminescence mechanism.
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PbS-doped CdS nanomaterials were successfully synthetized using chemical bath. Transmittance measurements were used to estimate the optical band gap energy. Tailing in the band gap was observed and found to obey Urbach rule. The diffraction X-ray (XRD) show that the size of cristallites is in the ~33 nm to 12 nm range. The peaks belonging to primary phase are identified at 20 = 26.5° and 20 = 26.00° corresponding to CdS and PbS respectively. Thus, a shift in maximum intensity peak from 20 = 26.4° to 28.2° is clear indication of possible transformation of cubic to hexagonal phase. Also peaks at 20 = 13.57°, 15.9° correspond to lead perchlorate thiourea. The effects on films thickness and substrate doping on the band gap energy and the width on tail were investigated. Increasing doping give rise to a shift in optical absorption edge ~0.4 eV
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In this work we investigate the excitonic properties of (4-FC6H4C2H4NH3)2PbI4 hybrid organic/inorganic thin films. We first use a standard point-by-point photoluminescence mapping. The maps formed using the photoluminescence intensity, line width, and broadening reveal the presence of structural defects. Using a statistical treatment of the data we found that the spatial fluctuations of the photoluminescence peak wavelengths are rather small compared to the photoluminescence line width. Moreover, we report the first direct observation of spatially resolved excitonic photoluminescence in this type of materials using dark-field imaging of white-light pumped photoluminescence. Owing to the rapid acquisition time of the dark-field images, their temperature dependence was studied, and the thermal behavior of the photoluminescence was investigated using this technique. We show that photoluminescence mapping combined with dark-field imaging and spectroscopy provides valuable information on the excitonic properties of hybrid organic/inorganic thin films.
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Nanocrystalline material
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