The formation of narrow size dispersed and nanometer size aggregates (clusters) of cadmium selenide (CdSe) quantum dots (QDs) and their temperature-sensitive photoluminescence (PL) spectral properties close to room temperature (298 K) are discussed. CdSe QDs formed stable clusters with an average diameter of ∼27 nm in the absence of coordinating solvents. Using transmission electron microscopy (TEM) imaging, we identified the association of individual QDs with 2−5 nm diameters into clusters of uniform size. A suspension of these clusters in different solvents exhibited reversible PL intensity changes and PL spectral shifts which were correlated with temperature. Although the PL intensity of CdSe QDs encapsulated in host matrixes and the solid state showed a response to temperature under cryogenic conditions, the current work identified for the first time QD clusters showing temperature-sensitive PL intensity variations and spectral shifts at moderate temperatures above room temperature. Temperature-sensit...

Temperature-sensitive photoluminescence of CdSe quantum dot clusters.

Synthesis and characterization of undoped and Mn2+ doped ZnS nanocrystallites (radius 2–3 nm) embedded in a partially densified silica gel matrix are presented. Optical transmittance, photoluminescence (PL), ellipsometric and electron spin resonance measurements revealed manifestation of quantum size effect. PL spectra recorded at room temperature revealed broad blue emission signal centred at ∼ 420 nm and Mn2+ related yellow-orange band centred at ∼ 590 nm while ESR indicated that Mn in ZnS was present as dispersed impurity rather than Mn cluster.

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Synthesis and characterization of sol-gel derived ZnS : Mn2+ nanocrystallites embedded in a silica matrix

Nanocrystalline undoped and Mn doped zinc sulphide (ZnS) thin films were synthesized by a wet chemical route without using any capping agent. The x-ray diffraction pattern showed the typical interplanar spacings corresponding to the cubic phase of ZnS. Transmission electron microscopy (TEM) studies confirmed the nanocrystalline nature with an average particle size  nm. Compositional information was obtained from the energy dispersive x-ray studies. A UV–visible optical spectroscopy study was carried out to determine the bandgap of the nanocrystalline ZnS and it showed a blue-shift with respect to the bulk value. Variation of bandgap energies with annealing temperature was also studied in detail. A photoluminescence (PL) study of the ZnS and ZnS:Mn films at room temperature (300 K) indicated a strong luminescence band at energy 2.07 eV.

http://iopscience.iop.org/article/10.1088/0957-4484/15/7/017/pdf

Synthesis and optical characterization of ZnS and ZnS:Mn nanocrystalline thin films by chemical route

Mn2+ doped In2S3–SiO2 nanocomposite thin films were synthesized by sol-gel technique. The films were annealed in air at different temperatures (473–623 K) and characterized by optical, microstructural and electron spin resonance (ESR) study. Optical transmittance study revealed the manifestation of quantum size effect while ESR indicated the presence of manganese in indium sulphide as dispersed dopant rather than manganese cluster.

Synthesis and characterization of sol-gel derived Mn 2+ doped In 2 S 3 nanocrystallites embedded in a silica matrix

Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique

We report on the observation of the quantum confinement effect by using photothermal deflection spectroscopy (PDS) experiment and the time dependence of optically induced degradation in CdS and CdSe semiconductor‐doped glasses. The observed absorption peaks in the PDS experiment, together with a simple model, were used to evaluate the average radius of semiconductor microcrystals. It is found that the estimated average radii of quantum dots are consistent with that obtained from other methods. This result demonstrates that the PDS technique provides an alternative tool for the study of the optical properties of semiconductor microscrystals. The time dependence of the luminescence degradation of the impurity band, which is attributed to the process of Auger ionization, follows a stretched‐exponential function. The inconsistency with the previously proposed exponential relaxation may be due to the size distribution of CdS and CdSe microcrystals.

Li‐Chi Liu

Papers

Photothermal deflection and photoluminescence studies of CdS and CdSe quantum dots