Tunable excitation properties of ZnCdS:Mn/ZnS quantum dots for cancer imaging

Water‐soluble ZnS:Mn quantum dots (QDs) were synthesized using a hydrothermal method with 3‐mercaptopropionic acid as stabilizer. The optical properties of ZnS:Mn QDs were thoroughly investigated by tuning the doping concentration of Mn²⁺ and the Zn/S precursor ratio, to obtain an optimal parameter for QDs with excellent fluorescence characteristics. ZnS:Mn QDs excited at only one wavelength, however, which seriously limited their further application. Here, a trace Cd ion was doped into a ZnS host, resulting in QD excitation covering a wide adjustable waveband. Furthermore, when a ZnS shell was coated onto the surface of the ZnCdS:Mn QDs, photoluminescence intensity and stability were further enhanced. After coupling with an anti‐CK 19 antibody, the ZnCdS:Mn/ZnS core/shell QDs were able to function by labeling cancer cells, indicating that they could be considered as a suitable bio‐probe for cells and tissue imaging.     

Deposition of CdS,CdS/ZnSe and CdS/ZnSe/ZnS shells around CdSeTe alloyed core quantum dots: effects on optical properties

In this work, we synthesized water‐soluble L ‐cysteine‐capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time‐resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrothermal synthesis for high‐quality glutathione‐capped CdxZn1 – xSe and CdxZn1 – xSe/ZnS alloyed quantum dots and its application in Hg(II) sensing

High‐quality Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS core/shell quantum dots (QDs) emitting in the violet–green spectral range have been successfully prepared using hydrothermal methods. The obtained aqueous Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs exhibit a tunable photoluminescence (PL) emission (from 433.5 nm to 501.2 nm) and a favorable narrow photoluminescence bandwidth [full width at half maximum (FWHM): 30–42 nm]. After coating with a ZnS shell, the quantum yield increases from 40.2% to 48.1%. These Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs were characterized by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy. To further understand the alloying mechanism, the growth kinetics of Cd_xZn_{1 – x}Se were investigated through measuring the fluorescence spectra and X‐ray diffraction spectra at different growth intervals. The results demonstrate that the inverted ZnSe/CdSe core/shell structure is formed initially after the injection of Cd²⁺. With further heating, the core/shell structured ZnSe/CdSe is transformed into alloyed Cd_xZn_{1 – x}Se QDs with the diffusion of Cd²⁺ into ZnSe matrices. With increasing the reaction temperature from 100 °C to 180 °C, the duration time of the alloying process decreases from 210 min to 20 min. In addition, the cytotoxicity of Cd_xZn_{1 – x}Se and Cd_xZn_{1 – x}Se/ZnS QDs were investigated. The results indicate that the as‐prepared Cd_xZn_{1 – x}Se/ZnS QDs have low cytotoxicity, which makes them a promising probe for cell imaging. Finally, the as‐prepared Cd_xZn_{1 – x}Se/ZnS QDs were utilized to ultrasensitively and selectively detect Hg²⁺ ions with a low detection limit (1.8 nM).     

Theoretical and experimental investigation of doping M in ZnSe (M = Cd,Mn, Ag,Cu) clusters: optical and bonding characteristics

The optical and bonding characteristics of doping ZnSe quantum dots (QDs) were investigated. Cd‐, Mn‐, Ag‐ and Cu‐doped ZnSe were synthesized in aqueous solution. Theoretically, the intensity of the Cd–Se bond was similar to that of the Zn–Se bond, which illustrates that Cd can be doped into ZnSe materials at any ratio. We found that Mn–Se bonding was stronger than Zn–Se bonding. Ag‐doped ZnSe nanoclusters show the same bonding and configuration as Cu‐doped ZnSe. Moreover, Cd can be doped into ZnSe using both the substitution‐ and vacancy‐doping method. For Mn‐doped ZnSe clusters, small amounts of Mn impurity lead to stronger bonding with Se, but larger amounts of Mn impurity led to the formation of a Mn–Mn metal bond. The theoretical results show that it is difficult to form a vacancy‐doping cluster for Mn‐doped ZnSe materials. In experiments, the absorption and photoluminescence (PL) spectral wavelengths of Mn‐doped ZnSe nanocrystals were the same as those of pure ZnSe nanocrystals, showing that the Mn impurity is not doped into ZnSe nanocrystals. Ag‐ and Cu‐doped ZnSe nanocrystals have the same PL characteristics. The doping of an impurity is related to the solubility product, and not the bonding intensity. Copyright © 2015 John Wiley & Sons, Ltd.     

Aqueous synthesis of CdTe/CdS/ZnS quantum dots and their optical and chemical properties

In this paper, we described a strategy for synthesis of thiol‐coated CdTe/CdS/ZnS (core–shell–shell) quantum dots (QDs) via aqueous synthesis approach. The synthesis conditions were systematically optimized, which included the size of CdTe core, the refluxing time and the number of monolayers and the ligands, and then the chemical and optical properties of the as‐prepared products were investigated. We found that the mercaptopropionic acid (MPA)‐coated CdTe/CdS/ZnS QDs presented highly photoluminescent quantum yields (PL QYs), good photostability and chemical stability, good salt tolerance and pH tolerance and favorable biocompatibility. The characterization of high‐resolution transmission electron microscopy (HRTEM), X‐ray powder diffraction (XRD) and fluorescence correlation spectroscopy (FCS) showed that the CdTe/CdS/ZnS QDs had good monodispersity and crystal structure. The fluorescence life time spectra demonstrated that CdTe/CdS/ZnS QDs had a longer lifetime in contrast to fluorescent dyes and CdTe QDs. Furthermore, the MPA‐stabilized CdTe/CdS/ZnS QDs were applied for the imaging of cells. Compared with current synthesis methods, our synthesis approach was reproducible and simple, and the reaction conditions were mild. More importantly, our method was cost‐effective, and was very suitable for large‐scale synthesis of CdTe/CdS/ZnS QDs for future applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Eu2+‐induced enhancement of defect luminescence of ZnS

The Eu²⁺‐induced enhancement of defect luminescence of ZnS was studied in this work. While photoluminescence (PL) spectra exhibited 460 nm and 520 nm emissions in both ZnS and ZnS:Eu nanophosphors, different excitation characteristics were shown in their photoluminescence excitation (PLE) spectra. In ZnS nanophosphors, there was no excitation signal in the PLE spectra at the excitation wavelength λ_ex > 337 nm (the bandgap energy 3.68 eV of ZnS); while in ZnS:Eu nanophosphors, two excitation bands appeared that were centered at 365 nm and 410 nm. Compared with ZnS nanophosphors, the 520 nm emission in the PL spectra was relatively enhanced in ZnS:Eu nanophosphors and, furthermore, in ZnS:Eu nanophosphors the 460 nm and 520 nm emissions increased more than 10 times in intensity. The reasons for these differences were analyzed. It is believed that the absorption of Eu²⁺ intra‐ion transition and subsequent energy transfer to sulfur vacancy, led to the relative enhancement of the 520 nm emission in ZnS:Eu nanophosphors. In addition, more importantly, Eu²⁺ acceptor‐bound excitons are formed in ZnS:Eu nanophosphors and their excited levels serve as the intermediate state of electronic relaxation, which decreases non‐radiative electronic relaxation and thus increases the intensity of the 460 nm and 520 nm emission dramatically. In summary, the results in this work indicate a new mechanism for the enhancement of defect luminescence of ZnS in Eu²⁺‐doped ZnS nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of highly luminescent and biocompatible CdTe/CdS/ZnS quantum dots using microwave irradiation: a comparative study of different ligands

We compared the effects of several ligands frequently used in aqueous synthesis, including L‐cysteine, L‐cysteine hydrochloride, N‐acetyl‐L‐cysteine (NAC), glutathione and 3‐mercaptopropionic acid, for microwave synthesis of CdTe quantum dots (QDs) in a sealed vessel with varied temperatures and times, and then developed a rapid microwave‐assisted protocol for preparing highly luminescent, photostable and biocompatible CdTe/CdS/ZnS core–multishell QDs. The effects of molecular structures of these ligands on QD synthesis under high temperatures were explored. Among these ligands, NAC was found to be the optimal ligand in terms of the optical properties of resultant QDs and reaction conditions. The emission wavelength of NAC‐capped CdTe QDs could reach 700 nm in 5 min by controlling the reaction temperature, and the resultant CdTe/CdS/ZnS core–multishell QDs could achieve the highest quantum yields up to 74% with robust photostability. In addition, the effects of temperature, growth time and shell–precursor ratio on shell growth were examined. Finally, cell culturing indicated the low cytotoxicity of CdTe/CdS/ZnS core–multishell QDs as compared to CdTe and CdTe/CdS QDs, suggesting their high potential for applications in biomedical imaging and diagnostics. Copyright © 2014 John Wiley & Sons, Ltd.     

Size‐dependent dual emission of Cu,Mn:ZnSe QDs: Controlling both emission wavelength and intensity

Cu,Mn:ZnSe quantum dots (QDs) of tunable size, controllable photoluminescence (PL) intensity ratio and PL range were prepared. A study of the experimental conditions confirmed that the size of Cu,Mn:ZnSe QDs is affected by the pH of the solution, the speed at which the Zn solution is injected and the reaction temperature. In general, high pH, low injection speed and high reaction temperature are optimal for preparing large QDs. Based on this knowledge, different sizes of Cu,Mn:ZnSe QDs were synthesized. Moreover, white emission Cu,Mn:ZnSe QDs were designed by controlling the experimental conditions and the feeding mole ratio of Mn:Cu.     

Synthesis of ZnSe and ZnSe:Cu quantum dots by a room temperature photochemical (UV‐assisted) approach using Na2SeO3 as Se source and investigating optical properties

In this study, ZnSe and ZnSe:Cu quantum dots (QDs) were synthesized using Na₂SeO₃ as the Se source by a rapid and room temperature photochemical (UV‐assisted) approach. Thioglycolic acid (TGA) was employed as the capping agent and UV illumination activated the chemical reactions. Synthesized QDs were successfully characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and UV–visible (UV–vis) spectroscopy, Fourier transform‐infrared (FT‐IR), and energy dispersive X‐ray spectroscopy (EDX). XRD analysis demonstrated the cubic zinc blend phase QDs. TEM images indicated that round‐shaped particles were formed, most of which had a diameter of about 4 nm. The band gap of the ZnSe QDs was higher than that for ZnSe in bulk. PL spectra indicated an emission with three peaks related to the excitonic, surface trap states and deep level (DL) states. The band gap and QD emission were tunable only by UV illumination time during synthesis. ZnSe:Cu showed green emission due to transition of electrons from the Conduction band (CB) or surface trap states to the ²T₂ acceptor levels of Cu²⁺. The emission was increased by increasing the Cu²⁺ ion concentration, such that the optimal value of PL intensity was obtained for the nominal mole ratio of Cu:Zn 1.5%.     

Comprehensive study of interaction between biocompatible PEG‐InP/ZnS QDs and bovine serum albumin

Polyethylene glycol (PEG) surface modified biocompatible InP/ZnS quantum dots (QDs) act as a potential alternative for conventional carcinogenic cadmium‐based quantum dots for in vivo and in vitro studies. Comprehensively, we studied the interaction between a model protein bovine serum albumin (BSA) and PEGylated toxic free InP/ZnS QDs using various spectroscopic tools such as absorption, fluorescence quenching, time resolved and synchronous fluorescence spectroscopic measurements. These studies principally show that tryptophan (Trp) residues of BSA have preferable binding affinity towards PEG‐InP/ZnS QDs surface and a blue shift in Trp fluorescence emission is a signature of conformational changes in its hydrophobic microenvironment. Photoluminescence (PL) intensity of Trp is quenched by ground state complex formation (static quenching) at room temperature. However, InP/ZnS@BSA conjugates become unstable with increasing temperature and PL intensity of Trp is quenched via dynamic quenching by PEG‐InP/ZnS QDs. Experimentally determined thermodynamic parameters for these conjugates have shown spontaneity, entropy driven and exothermic nature of bio‐conjugation. The calculated binding affinity (n ? 1, Hill coefficient) suggest that the affinity of InP/ZnS QDs for a BSA protein is not dependent on whether or not other BSA proteins are already bound to the QD surface. Energy transfer efficiency (E), Trp residue to InP/ZnS QDs distances and energy transfer rate (k_T) were all obtained from FÖrster resonance energy.     

Effect of concentration and shell thickness on the optical behavior of aqueous CdTe/ZnSe core/shell quantum dots (QDs) exposed to ionizing radiation

In this work CdTe/ZnSe core/shell quantum dots (QDs) were synthesized via a simple, rapid and room temperature photochemical approach. Optical properties of aqueous prepared CdTe/ZnSe QDs were studied systematically under gamma irradiation with dose range of 0 Gy to 20 kGy. The obtained results showed a regular red shift behavior versus gamma irradiation dose, in photoluminescence peak and absorption edge of the CdTe/ZnSe QDs. Structural properties of CdTe/ZnSe QDs before and after gamma irradiation were characterized by means of X-ray diffraction (XRD), Raman and Fourier-transform infrared (FT-IR) analyses. The obtained results showed that the crystalline structure of CdTe/ZnSe core/shell QDs did not change after gamma irradiation. Concentration and shell thickness as two important factors on the sensitivity of CdTe/ZnSe QDs in front of gamma irradiation have been investigated. Based on this study, CdTe/ZnSe QDs are suggested as good candidates for gamma dosimeter.     

Highly luminescent CdTe/CdS/ZnO core/shell/shell quantum dots fabricated using an aqueous strategy

To create core/shell/shell quantum dots (QDs) with high stability against a harmful chemical environment, CdTe/CdS QDs were coated with a ZnO shell in an aqueous solution. An interfaced CdS layer sandwiched between a CdTe core and ZnO shell provided relaxation of the strain at the core/shell interface since lattice parameters of CdS are intermediate between those of CdTe and ZnO. The photoluminescence (PL) peak wavelength of the core/shell/shell QDs was shifted from 569 to 615 nm by adjusting the size of CdTe cores and thickness of CdS and ZnO shells, along with the highest PL quantum yield of the core/shell/shell QDs reaching 80%, which implies promising applications in the field of biomedical labeling. Due to the decrease of surface defects, it was observed that PL lifetimes significantly increased at room temperature as follows: 29.6 34.2, and 47.5 ns for CdTe (537 nm), CdTe/CdS (555 nm) and CdTe/CdS/ZnO (581 nm) QDs, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Luminescence study on Mn,Ni co‐doped zinc sulfide nanocrystals

Zinc sulfide (ZnS) doped with transition metal has been used as phosphor for various optoelectronic applications. In the present report, ZnS:Mn doped and ZnS:Mn,Ni co‐doped were prepared using chemical co‐precipitation method using polyvinyl pyrolidone as a surfactant. The structural studies were carried out using an X‐ray diffraction technique; optical studies have been performed using ultraviolet–visible light absorption and photoluminescence (PL) spectroscopy. The presences of functional groups were confirmed using Fourier transform infrared spectroscopy. The X‐ray diffraction study and Reitveld analysis confirms the formation of cubic phase with crystalline size 2–3 nm for undoped and doped ZnS nanoparticles. A novel and enhanced luminescence characteristic have been observed in PL spectra. The luminescence intensity of Mn,Ni co‐doped ZnS in the blue region is much higher of that of ZnS. The PL results indicate that the doping of Ni creates shallow trap states or luminescence centres in the forbidden energy gap, which quenches the Mn states emission. Concentration quenching has been observed in Mn‐doped ZnS nanoparticles. From CIE coordinates, it is seen that the yellow and blue light emission of ZnS:Mn,Ni co‐doped nanophosphor may be a promising candidate for display devices and phosphor converted light‐emitting diode applications.     

Enantioselective cytotoxicity of ZnS:Mn quantum dots in A549 cells

Chirality strongly influences many biological properties of materials, such as cell accumulation, enzymatic activity, and toxicity. In the past decade, it has been shown that quantum dots (QDs), fluorescent semiconductor nanoparticles with unique optical properties, can demonstrate optical activity due to chiral ligands bound on their surface. Optically active QDs could find potential applications in biomedical research, therapy, and diagnostics. Consequently, it is very important to investigate the interaction of QDs capped with chiral ligands with living cells. The aim of our study was to investigate the influence of the induced chirality of Mn‐doped ZnS QDs on the viability of A549 cells. These QDs were stabilized with D‐ and L‐cysteine using a ligand exchange technique. The optical properties of QDs were studied using UV–Vis, photoluminescence (PL), and circular dichroism (CD) spectroscopy. The cytotoxicity of QDs was investigated by high content screening analysis. It was found that QDs stabilized by opposite ligand enantiomers, had identical PL and UV–Vis spectra and mirror‐imaged CD spectra, but displayed different cytotoxicity: QDs capped with D‐cysteine had greater cytotoxicity than L‐cysteine capped QDs.     

Characterization and cancer cell targeted imaging properties of human antivascular endothelial growth factor monoclonal antibody conjugated CdTe/ZnS quantum dots

High luminescence quantum yield water‐soluble CdTe/ZnS core/shell quantum dots (QDs) stabilized with thioglycolic acid were synthesized. QDs were chemically coupled to fully humanized antivascular endothelial growth factor₁₆₅ monoclonal antibodies to produce fluorescent probes. These probes can be used to assay the biological affinity of the antibody. The properties of QDs conjugated to an antibody were characterized by ultraviolet and visible spectrophotometry, fluorescent spectrophotometry, sodium dodecyl sulfate–polyacrylamide gel electrophoresis, transmission electron microscopy and fluorescence microscopy. Cell‐targeted imaging was performed in human breast cancer cell lines. The cytotoxicity of bare QDs and fluorescent probes was evaluated in the MCF‐7 cells with an MTT viability assay. The results proved that CdTe/ZnS QD–monoclonal antibody nanoprobes had been successfully prepared with excellent spectral properties in target detections. Surface modification by ZnS shell could mitigate the cytotoxicity of cadmium‐based QDs. The therapeutic effects of antivascular endothelial growth factor antibodies towards cultured human cancer cells were confirmed by MTT assay. Copyright © 2014 John Wiley & Sons, Ltd.     

CdTe1‐xSex/Cd0.5Zn0.5S core/shell quantum dots: core composition and property

Alloy CdTe_1‐xSe_x quantum dots (QDs) have been fabricated by an organic route using Cd, Te and Se precursors in a mixture of trioctylamine and octadecylphosphonic acid at 280 °C. The variation of photoluminescence (PL) peak wavelength of the CdTe_1‐xSe_x QDs compared with CdTe QDs confirmed the formation of an alloy structure. The Se component drastically affected the stability of CdTe_1‐xSe_x QDs. A Cd_0.5Zn_0.5S shell coating on CdTe_1‐xSe_x cores was carried out using oleic acid as a capping agent. CdTe_1‐xSe_x/Cd_0.5Zn_0.5S core/shell QDs revealed dark red PL while a yellow PL peak was observed for the CdTe_1‐xSe_x cores. The PL efficiency of the core/shell QDs was drastically increased (less than 1% for the cores and up to 65% for the core/shell QDs). The stability of QDs in various buffer solutions was investigated. Core/shell QDs can be used for biological applications because of their high stability, tunable PL and high PL efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

Near Infrared,Highly Efficient Luminescent Solar Concentrators

The fabrication of a low reabsorption emission loss, high efficient luminescent solar concentrator (LSC) is demonstrated by embedding near infrared (NIR) core/shell quantum dots (QDs) in a polymer matrix. An engineered Stokes shift in NIR core/shell PbS/CdS QDs is achieved via a cation exchange approach by varying the core size and shell thickness through the refined reaction parameters such as reaction time, temperature, precursor molar ratio, etc. The as‐synthesized core/shell QDs with high quantum yield (QY) and excellent chemical/photostability exhibit a large Stokes shift with respect to the bare PbS QDs due to the strong core‐to‐shell electrons leakage. The large‐area planar LSC based on core/shell QDs exhibits the highest value (6.1% with a geometric factor of 10) for optical efficiency compared to the bare NIR QD‐based LSCs and other reported NIR QD‐based LSCs. The suppression of emission loss and the broad absorption of PbS/CdS QDs offer a promising pathway to integrate LSCs and photovoltaic devices with good spectral matching, indicating that the proposed core/shell QDs are strong candidates for fabricating high efficiency semi‐transparent large‐area LSCs.     

Optical and structural characterization of CdS/ZnS and CdS:Cu2+/ZnS core–shell nanoparticles

Core‐shell CdS/ZnS (Zn 0.025?0.125 M) and CdS:Cu²⁺(1%)/ZnS nanoparticles were successfully synthesized using a chemical method. X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HR TEM), photoluminescence (PL) and UV/Visible (UV/Vis) techniques were used to characterize the novel CdS/ZnS and CdS:Cu²⁺/ZnS core–shell nanoparticles. All absorption peaks of the synthesized samples were highly blue‐shifted from the bulk CdS and ZnS. Very narrow and symmetric PL emission was observed in the yellow region for core–shell CdS/ZnS. Furthermore, the PL emission of CdS/ZnS was tuned into orange region by incorporate the Cu ion into the core CdS lattice. Copyright © 2013 John Wiley & Sons, Ltd.     

Fluorescent probe for detection of Cu2+ using core‐shell CdTe/ZnS quantum dots

Core‐shell CdTe/ZnS quantum dots capped with 3‐mercaptopropionic acid (MPA) were successfully synthesized in aqueous medium by hydrothermal synthesis. These quantum dots have advantages compared to traditional quantum dots with limited biological applications, high toxicity and tendency to aggregate. The concentration of Cu²⁺ has a significant impact on the fluorescence intensity of quantum dots (QDs), therefore, a rapid sensitive and selective fluorescence probe has been proposed for the detection of Cu²⁺ in aqueous solution. Under optimal conditions, the fluorescence intensity of CdTe/ZnS QDs was linearly proportional to the concentration of Cu²⁺ in the range from 2.5 × 10^–9 M to 17.5 × 10^–7 M with the limit of 1.5 × 10^–9 M and relative standard deviation of 0.23%. The quenching mechanism is static quenching with recoveries of 97.30–102.75%. Copyright © 2015 John Wiley & Sons, Ltd.     

CdSe and CdSe/CdS core–shell QDs: New approach for synthesis,investigating optical properties and application in pollutant degradation

In this work, CdSe quantum dots (QDs) were synthesized by a simple and rapid microwave activated approach using CdSO₄, Na₂SeO₃ as precursors and thioglycolic acid (TGA) as capping agent molecule. A novel photochemical approach was introduced for the growth of CdS QDs and this approach was used to grow a CdS shell around CdSe cores for the formation of a CdSe/CdS core–shell structure. The core–shells were structurally verified using X‐ray diffraction, transmission electron microscopy and FTIR (Fourier‐transform infrared (FTIR)) spectroscopy. The optical properties of the samples were examined by means of UV–Vis and photoluminescence (PL) spectroscopy. It was found that CdS QDs emit a broad band white luminescence between 400 to 700 nm with a peak located at about 510 nm. CdSe QDs emission contained a broad band resulting from trap states between 450 to 800 nm with a peak located at 600 nm. After CdS shell growth, trap states emission was considerably quenched and a near band edge emission was appeared about 480 nm. Optical studies revealed that the core–shell QDs possess strong ultraviolet (UV) ? visible light photocatalytic activity. CdSe/CdS core–shell QDs, showed an enhancement in photodegradation of Methyl orange (MO) compared with CdSe QDs.