CdSe-ZnS Core-shell Quantum Dots Research Articles

Far-Red Interlayer Excitons of Perovskite/Quantum-Dot Heterostructures.

Interlayer excitons (IXs) at the interface of heterostructures (HSs) with a staggered band alignment are fascinating quantum quasi-particles with light-emitting and long-lifetime characteristics. In this study, the energy band alignments (EBAs) of the HS of MAPbI3 perovskite thin sheets with CdSe-ZnS core-shell quantum dot (QD) layers are modulated by using different diameters of the QDs. Far-red IX emission is observed at 1.42eV from the HS of MAPbI3 /CdSe-ZnS-QD (λem =645nm) with type-II EBA owing to charge transfer. The lifetime of the far-red IXs is estimated to be 5.68µs, which is considerably longer than that (0.715ns) of the intralayer excitons from CdSe-ZnS-QD. With increasing incident excitation power, the PL peak and its intensity of IXs are blue-shifted and linearly increased, respectively, indicating a strong dipole alignment of far-red IXs at the heterojunction. Back focal plane imaging suggests that the directions of dipole moments of the IXs are relatively out-of-plane compared to those of the intralayer excitons (MAPbI3 and CdSe-ZnS-QD). Notably, the abnormal behavior of the optical characteristics is observed near the phase transition temperature (90K) of MAPbI3 . MAPbI3 /CdSe-ZnS-QD HS photodetectors show the increase in photocurrent and detectivity compared to MAPbI3 at IX excitation.

Luminescent Quantum Dots Stabilized by N-Heterocyclic Carbene Polymer Ligands

We have tested the ability of N-heterocyclic carbene (NHC)-modified ligands to coordinate and stabilize luminescent CdSe-ZnS core-shell quantum dot (QD) dispersions in hydrophilic media. In particular, we probed the effects of ligand structure and coordination number on the coating affinity to the nanocrystals. We find that such NHC-based ligands rapidly coordinate onto the QDs (requiring ∼5-10 min of reaction time), which reflects the soft Lewis base nature of the NHC groups, with its two electrons sharing capacity. Removal of the hydrophobic cap and promotion of carbene-driven coordination on the nanocrystals have been verified by 1H NMR spectroscopy, while 13C NMR was used to identify the formation of carbene-Zn complexes. The newly coated QD dispersions exhibit great long-term colloidal stability over a wide range of conditions. Additionally, we find that coordination onto the QD surfaces affects the optical and spectroscopic properties of the nanocrystals. These include a size-dependent red-shift of the absorption and fluorescence spectra and a pronounced increase in the measured fluorescence intensity when the samples are stored under white light exposure compared to those stored in the dark.

Fabrication and Evaluation of Electroluminescence Devices Using Quantum Dots As Light Emitting Materials

Colloidal quantum dots (QDs) have been attracting intense attention as promising candidates for new generation photoluminescent materials due to their fascinating optical properties, such as wide-band absorption, narrow-band emission, and high photoluminescence efficiency. These unique properties originate from semiconducting nature of the QD cores. The core is usually protected by an inorganic shell made of wider-gap semiconductors, resulting in photoluminescence quantum yield (PLQY) as high as 80%. CdSe-CdS and CdSe-ZnS core-shell QDs are such typical examples. Electroluminescence (EL) devices containing QDs in their emitting materials, which are known as QLEDs, have been demonstrated as a new type of display device providing better monochromaticity than conventional organic LED (OLEDs). However, the electroluminescence efficiencies of QLEDs have been inferior to that of OLEDs due probably to mismatch of the structure that has been developed based on OLEDs. Typically, the deep energy level of a valence band-edge (VB-edge) of the QDs hinders hole injection into QDs from HOMO of organic hole transport materials. Although developing new type of hole transport material is essential, one of the “indirect” strategies to solve this problem would be use of ZnO nanoparticles as an electron transport layer (ETL), which make use of deeper energy level of a VB-edge of ZnO nanoparticles. The resulting structure allows to accumulate holes in QD layer and facilitates hole injection into the QDs. However, the device structure of QLEDs still needs to be improved for more enhancing electroluminescence efficiencies. This study was carried out to design QLEDs structure which allows efficient charge injection into QDs by changing materials and thickness of the hole injection layer (HIL), and electron transport layer (ETL). The device performance was evaluated by voltage– current and voltage–luminance plots, and external quantum efficiency (EQE). CdSe-CdS-ZnS core-shell-shell nanoparticles used here were synthesized by the previously reported methods. Figure 1(a) shows the structure of the devices which consisted of layers of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): polystyrene (PEDOT:PSS, 6 nm)/poly(N-vinylcarbazole) (PVK, 37 nm)/CdSe-CdS-ZnS core-shell-shell QDs (14 nm)/ZnO nanoparticles (x nm)/LiF (1 nm)/Al (100 nm), where the thickness of the ZnO layer was varied between 10 nm and 70 nm. Except for LiF and Al layers, which was deposited using the vacuum thermal evaporation, each layer was sequentially formed on ITO-patterned glasses by spin-coating. Figure 1(b) shows the normalized EL spectrum of the QLEDs having an emission peak at 628 nm with a narrow full-width at half-maximum of 35 nm. The inset shows the picture of device (3×3 mm) demonstrating the formation of uniform emission. Figure 1(c) shows the voltage–luminance plots for CdSe-based QLEDs. The device of x = 12 nm only attained a maximum luminance of 298 cd/m2 and a maximum EQE of 0.063% although enough current was flowing (~100 mA). This result indicates the occurrence of charge imbalance, probably because the holes were leaked out to reach the cathode (Al) due to the insufficient ZnO nanoparticle layer thickness. Then, the thickness of ZnO nanoparticle layer was gradually increased to x=31, 48, 68 nm, raising steady the values of maximum luminance and EQE. These results suggested that the thickness of each layer might have effects on hole-electron balance. The hole-only and electron-only devices were fabricated using the same CdSe-CdS-ZnS core-shell-shell QDs and voltage–current curves were measured. The electron-only device passed larger current than the hole-only device, indicating the lower resistance for electron injection and transport than hole injection and transport. These facts corresponded with the previous results that increment of ZnO layer improved the device performance. Finally, the device was modified based on that with x = 68 nm. The use of PEDOT:PSS (HIL) having lower resistance were fabricated to further improve the charge balance. As a result, the device achieved a maximum luminance of 6500 cd/m2 and a maximum EQE of 1.3%. Figure 1

Binding energy of the hybrid exciton in heterostructures of colloidal CdSe-ZnS quantum dots and two-dimensional transition metal dichalcogenides

Using continuum model calculations within the framework of the $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ approach and effective mass approximation, we theoretically study the physical properties of the hybrid exciton state in type-II heterostructures composed of two-dimensional monolayer transition metal dichalcogenides (2D TMDs) and zero-dimensional (0D) CdSe-ZnS core-shell quantum dots (QDs). Interactions between an electron located in the lowest unoccupied molecule orbital (LUMO) state of the QD and a hole in the valence band of the 2D TMD along with their effects on charge distribution and exciton binding energy are self-consistently calculated via solving the Schr\odinger and Poisson equations. We show that (i) the hole wave function of the 2D TMD is tightly bounded within several unit cells by an electron located in the LUMO state of the QD while the distribution of the electron wave function is marginally changed by the Coulomb attraction from the hole in the 2D TMD; (ii) the binding energies of the hybrid exciton decrease from 110 to 25 meV with the radius of the CdSe core increasing from 2 to 8 nm, which is several times lower than that of the exciton of 2D TMDs; and (iii) the exciton binding energies of heterostructures composed by different 2D TMD materials are similar. We explain the size dependence of exciton binding energy as the result of the delocalization of the electron wave function with QD size and attribute the similar binding energy obtained in different 2D/0D heterostructures to the weak dielectric screening effect of different 2D TMDs on electron-hole interaction. These results indicate that the physical properties of a hybrid exciton in 2D/0D heterostructures is dominated by the properties of the QD instead of the 2D TMDs. We further compare our calculated exciton binding energy with the corresponding experimental result; good agreement between experiment and theory provides evidence for the validity of our theoretical approach.

Spatial energy transfer with observation of bimolecular singlet oxygen emission using quantum dots as donors and zinc-phthalocyanine as acceptors.

This study reports the influence of CdSe-ZnS core-shell quantum dots (QDs) for formation of singlet oxygen using zinc-phthalocyanine (ZnPc) dyes in colloidal solutions. Using a microluminescence surface scan technique it was possible to measure accurately the photon diffusion length, or photon mean free path, inside the medium. Analyses were performed for a range of QD concentrations. Photon diffusion length was assigned to the bimolecular singlet oxygen emission at 707 nm. Related singlet oxygen emission was predicted by observing quenching of the photon diffusion length measured at the specific oxygen emission as a function of QD concentration, being a nontrivial phenomenon related to the QD donors. Diffusion length measured at 707 nm increased with QD concentration; in the absence of QDs, as in pure ZnPc samples, the emission peak at 707 nm was not observed.

Structural and chemical characterization of CdSe-ZnS core-shell quantum dots

The structural and compositional properties of CdSe-ZnS core-shell quantum dots (QDs) with a sub-nm shell thickness are analyzed at the atomic scale using electron microscopy. QDs with both wurtzite and zinc blende crystal structures, as well as intermixing of the two structures and stacking faults, are observed. High-angle annular dark-field scanning transmission electron microscopy suggests the presence of a lower atomic number epitaxial shell of irregular thickness around a CdSe core. The presence of a shell is confirmed using energy dispersive X-ray spectroscopy. Despite the thickness irregularities, the optical properties of the particles, such as photoluminescence and quantum yield, show clear enhancement after growth of the ZnS shell.

Optical Energy Transfer from Photonic Nanowire to Plasmonic Nanowire

Rational and versatile transfer of optical energy from photonic nanowire to plasmonic nanowire is highly desirable and extremely challengeable. Herein, we demonstrate that optical energy transfer from CdSe–ZnS core–shell quantum dots doped polymer photonic nanowire to silver plasmonic nanowire with an efficiency of 32 ± 1.5% via the Forster resonance energy transfer process. The quantum dots with an emission at 650 nm wavelength were embedded in polymer nanowire and were excited by a 532 nm green laser. In the crossing region of the photonic nanowire and plasmonic nanowire, propagated surface plasmons of silver nanowire can be effectively excited by the emitted light from quantum dots embedded in polymer nanowire. This energy transfer between photonic and plasmonic nanowires would provide potential applications in optical interconnection.

Characterization of the Ligand Capping of Hydrophobic CdSe–ZnS Quantum Dots Using NMR Spectroscopy

We have combined a few advanced solution phase NMR spectroscopy techniques, namely, 1H, 31P, heteronuclear single quantum coherence (HSQC), and diffusion ordered spectroscopy (DOSY), to probe the composition of the organic capping layer on colloidal CdSe–ZnS core–shell quantum dots grown via the “hot injection” route. Combining solution phase 31P and 1H NMR with DOSY, we are able to distinguish between free ligands and those coordinated on the QD surfaces. Furthermore, when those NMR measurements are complemented with matrix-assisted laser desorption ionization (MALDI) and FTIR data, we find that the organic shell of the as-prepared QDs consists of a mixture of tri-n-octylphosphine oxide (TOPO), tri-n-octylphosphine (TOP), alkyl amine, and alkyl phosphonic acid (L- and X-type ligands); the latter molecules are usually added during growth at a rather small concentration to improve the quality of the prepared nanocrystals. However, NMR data collected from QD dispersions subjected to two or three rounds of p...

Temperature sensing using CdSe quantum dot doped poly(methyl methacrylate) microfiber.

This work describes noncontact temperature measurements using wavelength shifts of CdSe quantum dot (QD) doped poly(methyl methacrylate) microfiber. The sensor is fabricated using a drawing method by bridging two tapered single mode fibers with a polymer microfiber (PMF) approximately 3μm in diameter. A set of a PMF section with and without the doping of the CdSe-ZnS core-shell QD was applied as sensing probes and used to measure temperatures over the range of 25°C-48°C. The experimental results show that the doped PMF is able to achieve a higher performance with a reasonably good sensitivity of 58.5pm/°C based on the wavelength shifting, which is about 18 times that of the undoped PMF temperature sensitivity. The proposed sensor showed a linear temperature sensing range that matches well with the physiologically relevant temperatures. Moreover, these results open the way for long-term and high-stability realization of temperature sensing optical fibers.

Temperature-dependent resonance energy transfer from CdSe–ZnS core–shell quantum dots to monolayer MoS2

We investigated the temperature-dependent resonance energy transfer (ET) from CdSe–ZnS core–shell quantum dots (QDs) to monolayer MoS2. QDs/MoS2 structures were fabricated using a spin-coating method. Photoluminescence (PL) spectra and decay curves of the QDs/MoS2 structures were measured in the temperature range of 80−400 K. The results indicate that the PL intensity of the QDs decreased approximately 81% with increasing temperature, whereas that of the MoS2 increased up to a maximum of 78% at 300 K because of the combined effect of thermal quenching and the ET in the QDs/MoS2 structures. The ET efficiency and ET rate also exhibited similar variation trends, both increased with increasing temperature from 80 to 260 K and then decreased until 400 K, resulting in a maximum ET efficiency of 22% and an ET rate of 1.17 ns–1 at ~260 K. These results are attributed to the varied distribution of the localized excitons and free excitons in the QDs/MoS2 structures with increasing temperature.

The Fabrication of the Infrared CdSe Doped With Cu Photodetector

In this work, the implementation method of the CdSe doped with Cu (CdSe: Cu) photodetector is presented. This detector is prepared by vacuum evaporation of CdSe films on glass substrate followed by vacuum annealing under an argon atmosphere for doping with copper. This detector is found, for the first time, to cover a wide range of the infrared besides the visible region of the electromagnetic spectrum. This finding of the wavelength tuning is due to the localized energy states of copper atoms inside the band gap of the CdSe. This tuning is compared with recent work in the corresponding colloidal CdSe-ZnS core shell quantum dots and with the quantum well (QWIR) and quantum dots (QDIR) infrared detectors. The major significance of this developed detector is in its synthesis simplicity and its fabrication processes costs in comparison with that of the (QWIR) and (QDIR) detectors. The structural analysis results demonstrated that the vacuum annealing in competition with the doping concentration improves significantly the film structure. Better crystalline structure was reported at 5 wt% of Cu concentration and at annealing temperature of 350 ºC. Besides the measured detectivity at room temperature is D*=2.31×108 cm Hz1/2W-1. This value approaches the detectivity of the state of art mercury cadmium telluride (MCT). This result paves the way for further investigations and improvements.

Acid Dissociation of 3-Mercaptopropionic Acid Coated CdSe–CdS/Cd0.5Zn0.5S/ZnS Core–Multishell Quantum Dot and Strong Ionic Interaction with Ca2+ Ion

By devising careful electrophoresis, it was shown that at pH below 7.0, the electrophoretic mobility of 3-mercaptopropionic acid (3MPA) coated CdSe–ZnS core–shell quantum dots (denoted as QD-3MPA) was very small. At pH above 7.0, QD-3MPA migrated toward the anode, implying acid dissociation, and the degree of which was proportional to the pH value. QD-3MPA’s electrophoretic mobility was impaired after adding sufficient Ca2+ ions to the QD solution and revived when a similar amount of Ca2+ chelators (ethylene glycol tetraacetic acid, EGTA) was added. This demonstrated that acid dissociation and its pH dependence of 3MPA on the QD surface are critical factors in understanding the electric and optical properties of QDs. The acid dissociated QD-3MPA interacted strongly with Ca2+, forming a charge neutral QD-3MPA–Ca2+ complex in the absence of EGTA. First-principles study confirmed the observed experimental evidence. The strong ionic interaction between acid dissociated QD-3MPA and Ca2+ is critical for develop...

Exciton delocalization and hot hole extraction in CdSe QDs and CdSe/ZnS type 1 core shell QDs sensitized with newly synthesized thiols.

The present work describes ultrafast thermalized and hot hole transfer processes from photo-excited CdSe quantum dots (QDs) and CdSe/ZnS core-shell QDs (CSQDs) to newly synthesized thiols. Three thiols namely 2-mercapto-N-phenylacetamide (AAT), 3-mercapto-N-phenylpropanamide (APT) and 3-mercapto-N-(4-methoxyphenyl) propanamide (ADPT) were synthesized and their interaction with both CdSe QDs and CdSe/ZnS CSQDs was monitored. Steady state absorption study suggests the exciton delocalization from CdSe QDs in the presence of the thiols. However similar features were not observed in the presence of a ZnS shell over a CdSe core, instead a broadening in the excitonic peak was observed with both APT and ADPT but not with AAT. This exciton delocalization and broadening in the excitonic peak was also confirmed by ultrafast transient absorption studies. Steady state and time resolved emission studies show hole transfer from photo-excited QDs and CSQDs to the thiols. A signature of hot hole extraction was observed in transient absorption studies which was confirmed by fluorescence upconversion studies. Both hot and thermalized hole transfer rates from CdSe QDs and CdSe/ZnS CSQDs to the thiols were determined using the fluorescence up-conversion technique. Experiments with different ZnS shell thicknesses have been carried out which suggest that hole transfer is possible till 2.5 monolayer of the ZnS shell. To the best of our knowledge we are reporting for the first time the extraction of hot holes from CdSe/ZnS type I CSQDs by a molecular adsorbate.

Quantum dot assisted tracking of the intracellular protein Cyclin E in Xenopus laevis embryos.

BackgroundLuminescent semiconductor nanocrystals, also known as quantum dots (QD), possess highly desirable optical properties that account for development of a variety of exciting biomedical techniques. These properties include long-term stability, brightness, narrow emission spectra, size tunable properties and resistance to photobleaching. QD have many promising applications in biology and the list is constantly growing. These applications include DNA or protein tagging for in vitro assays, deep-tissue imaging, fluorescence resonance energy transfer (FRET), and studying dynamics of cell surface receptors, among others. Here we explored the potential of QD-mediated labeling for the purpose of tracking an intracellular protein inside live cells.ResultsWe manufactured dihydrolipoic acid (DHLA)-capped CdSe-ZnS core-shell QD, not available commercially, and coupled them to the cell cycle regulatory protein Cyclin E. We then utilized the QD fluorescence capabilities for visualization of Cyclin E trafficking within cells of Xenopus laevis embryos in real time.ConclusionsThese studies provide “proof-of-concept” for this approach by tracking QD-tagged Cyclin E within cells of developing embryos, before and during an important developmental period, the midblastula transition. Importantly, we show that the attachment of QD to Cyclin E did not disrupt its proper intracellular distribution prior to and during the midblastula transition. The fate of the QD after cyclin E degradation following the midblastula transition remains unknown.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0092-6) contains supplementary material, which is available to authorized users.

Tuning the Redox Coupling between Quantum Dots and Dopamine in Hybrid Nanoscale Assemblies

We explored the charge transfer interactions between CdSe–ZnS core–shell quantum dots (QDs) and the redox active neurotransmitter dopamine, using covalently assembled QD–dopamine conjugates. We combined steady-state fluorescence, time-resolved fluorescence, and transient absorption bleach measurements to probe the effects of changing the QD size (thus the QD energy levels) and the conjugate valence on the rate of QD photoluminescence quenching when the pH of the medium was adjusted from acidic to alkaline. We measured substantially larger quenching efficiencies, combined with more pronounced shortening of the carrier dynamics of these assemblies for smaller size QDs and in alkaline pH. Moreover, we found that changes in the QD size alter the electron and hole relaxation of photoexcited QDs but with different extents. For instance, a pronounced change in the hole relaxation was measured in alkaline buffers. Moreover, the hole relaxation was faster for conjugates of green-emitting QDs as compared to their r...

Effect of ZnS shell on optical properties of CdSe–ZnS core–shell quantum dots

A modified microemulsion technique was used to synthesize CdSe–ZnS core–shell quantum dots (QDs) of ∼5nm diameter. Their nonlinear optical absorption was observed with nanosecond laser radiation of 532-nm wavelength. Linear optical studies show confinement effects. There is a new emission band around 745nm under excitation of 532nm which is an indication of the generation of deep trap states in CdSe QDs. As the ZnS shell thickness increases, there could be an increased electron–hole pair generation leading to large free-carrier concentration which in turn results in enhancement of nonlinear optical absorption. In addition, it was found that the optical limiting threshold gets decreased as the ZnS shell thickness increases.

Fluorescence resonance energy transfer measured by spatial photon migration in CdSe-ZnS quantum dots colloidal systems as a function of concentration

The study of the spatial photon migration as a function of the concentration brings into attention the problem of the energy transfer in quantum dot embedded systems. By measuring the photon propagation and its spatial dependence, it is possible to understand the whole dynamics in a quantum dot system, and also improve their concentration dependence to maximize energy propagation due to radiative and non-radiative processes. In this work, a confocal microscope was adapted to scan the spatial distribution of photoluminescence from CdSe-ZnS core-shell quantum dots in colloidal solutions. The energy migration between the quantum dots was monitored by the direct measurement of the photon diffusion length, according to the diffusion theory. We observed that the photon migration length decreases by increasing the quantum dot concentration, this kind of behavior has been regarded as a signature of Förster resonance energy transfer in the system.

Absorption spectra of CdSe–ZnS core–shell quantum dots at high photon energies: Experiment and modeling

Absorption spectra of CdSe–ZnS core–shell quantum dot (QD) ensembles, with average core diameters ranging from 2.6nm to 7.2nm have been obtained using both transmission and photoluminescence excitation measurements. In agreement with previous reports, the absorption coefficient at energies ≃1eV above the effective bandgap increases monotonically as in bulk solids. A simple effective-mass spherical core–shell potential model cannot explain the relatively high absorption at higher energies. The calculated electron and hole radial envelope wavefunctions show asymmetry due to the core–shell structure. It leads to normally symmetry-disallowed transitions acquiring a weak oscillator strength, with their number and strength increasing with energy. A phenomenological model that invokes normally disallowed transitions in general is shown to reproduce the absorption spectrum at higher energies quite well. The oscillator strength scaling factor for such transitions increases with decrease in QD size, consistent with expectations.

Multifunctional quantum dot-polypeptide hybrid nanogel for targeted imaging and drug delivery.

A new type of multifunctional quantum dot (QD)-polypeptide hybrid nanogel with targeted imaging and drug delivery properties has been developed by metal-affinity driven self-assembly between artificial polypeptides and CdSe-ZnS core-shell QDs. On the surface of QDs, a tunable sandwich-like microstructure consisting of two hydrophobic layers and one hydrophilic layer between them was verified by capillary electrophoresis, transmission electron microscopy, and dynamic light scattering measurements. Hydrophobic and hydrophilic drugs can be simultaneously loaded in a QD-polypeptide nanogel. In vitro drug release of drug-loaded QD-polypeptide nanogels varies strongly with temperature, pH, and competitors. A drug-loaded QD-polypeptide nanogel with an arginine-glycine-aspartic acid (RGD) motif exhibited efficient receptor-mediated endocytosis in αvβ3 overexpressing HeLa cells but not in the control MCF-7 cells as analyzed by confocal microscopy and flow cytometry. In contrast, non-targeted QD-polypeptide nanogels revealed minimal binding and uptake in HeLa cells. Compared with the original QDs, the QD-polypeptide nanogels showed lower in vitro cytotoxicity for both HeLa cells and NIH 3T3 cells. Furthermore, the cytotoxicity of the targeted QD-polypeptide nanogel was lower for normal NIH 3T3 cells than that for HeLa cancer cells. These results demonstrate that the integration of imaging and drug delivery functions in a single QD-polypeptide nanogel has the potential for application in cancer diagnosis, imaging, and therapy.

CdSe-ZnS Core-Shell Quantum Dots: Surface Plasmons Effect and Optical Spectra

Absorption and photoluminescence (PL) spectra of a colloidal CdSe-ZnS core-shell quantum dots (QDs) were measured within the strong confinement regime. The QDs were casted on half-coated quartz substrates with 50 nm of gold and prepared for studying the surface plasmons effect. The samples were optically arranged and pumped by different wavelengths, and the PL spectra were detected. Excitation with a wavelength of 400 nm reveals a structure fluorescence spectrum which consists of five distinct bands. These bands are more intense and resolved than the corresponding traditional weak absorption bands. They were detected for the first time and assigned according to the theoretical predictions of excitons in a spherical potential with Coulomb interactions and valence bands mixing. A scheme based on multiple exciton generation (MEG) for the appearance of the fluorescence bands was proposed. This scheme was confirmed by the recent theoretical prediction using the state-of-the art time domain ab initio density functional theory and the atomistic pseudopotential calculations. The detected surface plasmons effect in QDs enhances the intensity of the fluorescence bands. This surface plasmons effect facilitated the appearance of these mentioned bands in more intensive features than the corresponding traditional weak absorption bands. Furthermore, the reduction in the measured lifetime of the first excited electronic state from 20 ns for the QDs deposited directly on the quartz substrate to 7 ns for the QDs casted on the gold film, gives a further evidence of the surface plasmons effect in the (PL) of the CdSe-ZnS QDs.