Photoluminescence Of CdTe Quantum Dots Research Articles

Tuning the photoluminescence of CdTe quantum dots by controllable coupling to plasmonic Au nanoparticles

A controllable variation of the photoluminescence (PL) intensity of semiconductor quantum dots (QDs) via their coupling to plasmonic nanoparticles (NPs) is the potential basis for optoelectronic and sensing applications. In this work, the effect of Au NPs on the PL of colloidal CdTe QDs is investigated in solution and solid films. An PL enhancement for the QDs synthesized in water was observed in case of spectral overlap of the plasmon absorption band of and QD PL band. In case of Au NPs synthesized in dimethyl sulfoxyl the trend is to reduction of the PL intensity. For the reference samples prepared by mixing QDs not with Au NP solutions but with corresponding pure solvent, certain PL enhancement was observed and presumably attributed to reduction of self-absorption or non-radiative interparticle interaction in less concentrated QD solution. However, the contribution of this dilution-related enhancement is expected to be independent of the spectral properties of NPs and QDs. Therefore, the observed in this work different behavior of QD PL in certain combinations of QDs and NPs is attributed to interaction between electronic excitation in the QD and plasmon.

Optical properties and charge carrier dynamics of CdTe quantum dots in silicate glasses

CdTe quantum dots (QDs) in silicate glasses were fabricated through conventional melt-quenching and heat-treatment; steady-state and transient optical properties of CdTe QDs were investigated. CdTe QDs with diameters of 2.3–5.9 nm with photoluminescence in the range of 553–768 nm were precipitated in the glasses. Time-resolved photoluminescence and transient absorption analysis showed that photoluminescence of CdTe QDs was composed of intrinsic emission and defect emission. Oxidation of Te2− and formation of Te2 during thermal treatment led to the unpassivated Cd2+ on the surface of CdTe QDs and formation of shallow trapping states. The photo-generated electrons were trapped by the shallow surface states of CdTe QDs within 0.4±0.03 ps, and Auger recombination processes occurred within a timescale of 3.2±0.35 ps. Both intrinsic emission and defect emission with effective lifetimes of several nanoseconds and dozens of nanoseconds were observed.

The Influence of Surface Modification on the Photoluminescence of CdTe Quantum Dots: Realization of Bio-Imaging via Cost-Effective Polymer.

To impart biocompatibility, stability, and specificity to quantum dots (QDs)-and to reduce their toxicity-it is essential to carry out surface modification. However, most surface-modification processes are costly, complicated, and time-consuming. In addition, the modified QDs often have a large size, which leads to easy aggregation in biological environments, making it difficult to excrete them from in vivo systems. To solve these problems, three kinds of conventional polymers, namely, polyvinyl alcohol (PVA, neutral), sodium polystyrene sulfonate (PSS, negative charged), and poly(diallyl dimethyl ammonium chloride) (PDDA, positive charged) were selected to modify the surface of QDs at low cost via a simple process in which the size of the QDs was kept small after modification. The effect of polymer modification on the photoluminescence (PL) properties of the QDs was systematically investigated. High quantum yields (QYs) of 65 % were reached, which is important for the realization of bio-imaging. Then, the cytotoxicity of CdTe QD-polymer composites was systematically investigated via MTT assay using the Cal27 and HeLa cell lines, especially for high concentrations of QD-polymer composites in vitro. The experimental results showed that the cytotoxicity decreased in the order CdTe-PDDA>CdTe>CdTe-PSS>CdTe-PVA, indicating that PSS and PVA can reduce the toxicity of the QDs. An obvious cytotoxicity of CdTe-PVA and CdTe-PSS was present until 120 h for the Cal27 cell line and until 168 h for the HeLa cell line. At last, the Cal27 cell line was selected to realize bio-imaging using CdTe-PSS and CdTe-PVA composites with different emission colors under one excitation wavelength.

Use of CdTe quantum dots for high temperature thermal sensing

Thermal sensitive photoluminescence of CdTe quantum dots was used for micro-electromechanical systems temperature measurements in the high temperature range.

Synchronous determination of mercury (II) and copper (II) based on quantum dots-multilayer film

A sensitive sensor for mercury (II) and copper (II) synchronous detection was established via the changed photoluminescence of CdTe quantum dots (QDs) multilayer films in this work. QDs were deposited on the quartz slides to form QDs-multilayer films by electrostatic interactions with poly(dimethyldiallyl ammonium chloride) (PDDA). Hg 2+ or Cu 2+ could quench the photoluminescence of the QDs-multilayer films, and glutathione (GSH) was used to remove Hg 2+ or Cu 2+ from QDs-multilayer films due to strong affinity of GSH-metal ions, which resulted in the recovered photoluminescence of QDs-multilayer films. There are good linear relationships between the metal ions concentration and the photoluminescence intensity of QDs in the quenched and recovered process. It was found that the Stern–Volmer constants for Hg 2+ are higher than that for Cu 2+. Based on different quenching and recovery constant between Hg 2+ and Cu 2+, the synchronous detection of Hg 2+ and Cu 2+ can be achieved. The linear ranges of this assay were obtained from 0.005 to 0.5 μM for Hg 2+ and from 0.01 to 1 μM for Cu 2+, respectively. And the artificial water samples were determined by this method with satisfactory results, the recoveries for Hg 2+ and Cu 2+ ions were found in the range of 90.4–106.4%. To the best of our knowledge, it is the first report about the synchronous detection of Hg 2+ and Cu 2+ by using quenched and recovered photoluminescence of quantum dots multilayer films.

Photoluminescence of CdTe quantum dots ligated with caprylic acid synthesized at low temperature

Photoluminescent semiconductor nanocrystals or quantum dots (QDs) are usually produced using expensive ligands and solvents at high temperature above 280°C to ensure high-quality optical properties, particularly the photoluminescence of QDs. The reproducibility of highly stable photoluminescence in QD preparation, in most cases, varies depending on many effects, such as the ligand used and temperature. Here a facile preparation of photoluminescent semiconductor CdTe nanocrystals or quantum dots (QDs) is conducted in the presence of caprylic acid at moderate temperatures between 80–140°C, which are much lower than the high temperatures used in conventional organic-phase preparation of CdTe QDs. The results show that the optical properties of CdTe QDs depend considerably on the reaction time, temperature and ligand used.

Ionic Liquids (ILs) Detection Based on its Enhancing Effect on the Photoluminescence of CdTe Quantum Dots (QDs)

In this paper, a method for the determination of ILs, specifically 1-butyl-3-methyl imidazolium bromide( BMIB), was developped using mercaptoacetic acid (MAA) capped CdTe QDs as fluorescence probe. Under optimum conditions, the enhancement of fluorescence intensity of CdTe QDs was linearly in proportion to the concentration of BMIBin the range of 9.1x10-5-1.1x10-2 mol L-1 with a correlation coefficient of 0.996. The detection limit was 6.9x10-5 mol L-1. The proposed method was applied to the determination of trace BMIB in river water and tap water samples with satisfactory results. Keywords: Ionic liquids, 1-Butyl-3-methylimidazolium bromide, CdTe quantum dots, Fluorescence enhancement

Synthesis and Spectral Studies of CdTe-Dendrimer Conjugates.

In order to couple high cellular uptake and target specificity of dendrimer molecule with excellent optical properties of semiconductor nanoparticles, the interaction of cysteine-capped CdTe quantum dots with dendrimer was investigated through spectroscopic techniques. NH2-terminated dendrimer molecule quenched the photoluminescence of CdTe quantum dots. The binding constants and binding capacity were calculated, and the nature of binding was found to be noncovalent. Significant decrease in luminescence intensity of CdTe quantum dots owing to noncovalent binding with dendrimer limits further utilization of these nanoassemblies. Hence, an attempt is made, for the first time, to synthesize stable, highly luminescent, covalently linked CdTe–Dendrimer conjugate in aqueous medium using glutaric dialdehyde (G) linker. Conjugate has been characterized through Fourier transform infrared spectroscopy and transmission electron microscopy. In this strategy, photoluminescence quantum efficiency of CdTe quantum dots with narrow emission bandwidths remained unaffected after formation of the conjugate.

Two distinct photoluminescence responses of CdTe quantum dots to Ag (I)

Four sizes of water-soluble thiol-capped CdTe quantum dots (QDs) have been synthesized and used to investigate the photoluminescence (PL) responses to Ag + ions. For small particles, the CdTe QDs exhibit PL enhancement in the presence of lower concentration of Ag + but show obvious quenching with the further increase of Ag +; for larger particles, however, PL of CdTe QDs is quenched all the time with the Ag + addition, no PL enhancement is observed. Mechanism study shows that small QDs with more traps on the particle surface are effectively passivated by initial adsorbed Ag +, which accounts for the PL enhancement observed; after the initial traps are saturated, the excess Ag + facilitates nonradiative recombination, resulting in PL quenching. For larger particles, the nonradiative recombination dominates the whole process even for the lower concentration of Ag +, due to the fewer traps on the QD surface. Compared with larger particles, the small CdTe QDs are more suitable for sensing Ag + because of the more sensitive and selective PL response. To our best knowledge, this is the first systematical study on the interaction of Ag + with different-sized CdTe QDs.

Optical properties of Ag/CdTe nanocomposite self-organized by electrostatic interaction

Ag/CdTe nanocomposite was prepared via self-organization process by electrostatic interaction between positively charged CdTe quantum dots and negatively charged Ag nanoparticles and examined with respect to their optical properties. The positively charged CdTe quantum dots and negatively charged Ag nanoparticles were synthesized separately by modifying nanoparticles surface with cationic and anionic thiol compounds, respectively. The result showed that the mixing ratio of Ag nanoparticles to CdTe quantum dots is an important parameter for controlling resulting composites. The resulting solution is optically transparent if one component is in excess. Photoluminescence of CdTe quantum dots undergoes considerably quenching if CdTe nanocrystals are in excess and SERS spectra of BVPP absorbed on Ag colloid became stronger if Ag nanoparticles are in excess. Nevertheless, while the ratio is approximately 1, micrometer-sized solid composite is obtained with the elapse of 1 h after mixing. SERS spectra for solid composite only exhibit the signals of the CdS nanocrystal which reflected that prolonged refluxing during the synthesis leads to a partial hydrolysis of the thiols and to the incorporation of the sulfur from the thiol molecules into the the growing nanoparticles to form mixed CdTe(S) nanocrystal, similar to CdTe/CdS core/shell structure. From the results, we conclude that optical properties of Ag/CdTe are dependent on the mixing ratio of both nanoparticles.