CdSe/ZnS nanocrystals

Talapin, D. V., Rogach, A. L, Kornowski, A., Haase, M. and Weller, H. (2001) Highly luminescent monodisperse CdSe and CdSe/ZnS nanocrystals synthesized in a hexadecylamine-trioctylphosphine oxide-trioctylphospine mixture. Nano Lett., 1, 207-211. 

Ebenstein Y, Mokari T, Banin U (2002) Fluorescence quantum yield of CdSe/ZnS nanocrystals investigated by correlated atomic-force and single-particle fluorescence microscopy. Appl Phys Lett 80 4033 1035... 

Lee SY, Nakaya K, Hayashi T, Hara M (2009) Quantitative study of the gold-enhanced fluorescence of CdSe/ZnS nanocrystals as a function of distance using an AFM probe. Phys Chem Chem Phys 11 4403-9... 

Snee PT, Somers RC, Nair G, Zimmer JP, Bawendi MG, Nocera DG (2006) A ratiometric CdSe/ZnS nanocrystal pH sensor. J Am Chem Soc 128 13320-1... 

In this section we analyze experimental data and make comparisons with theory. Data were obtained for 100 CdSe-ZnS nanocrystals at room temperature.1 We first performed data analysis (similar to standard approach) based on the distribution of on and off times and found that a+= 0.735 0.167 and v = 0.770 0.106,2 for the total duration time T = T = 3600 s (bin size 10 ms, threshold was taken as 0.16 max I(t) for each trajectory). Within error of measurement, a+ a k 0.75. The value of a 0.75 implies that the simple diffusion model with a = 0.5 is not valid in this case. An important issue is whether the exponents vary from one NC to another. In Fig. 13 (top) we show the distribution of a obtained from data analysis of power spectra. The power spectmm method [26] yields a single exponent apSd for each stochastic trajectory (which is in our case a+ a apSd). Figure 13 illustrates that the spread of a in the interval 0 < a < 1 is not large. Numerical simulation of 100 trajectories switching between 1 and 0, with /+ (x) = / (x) and a = 0.8, and with the same number of bins as the experimental trajectories, was performed and the... 

The evolution of optical phonon spectra of colloidal core/shell CdSe/ZnS nanocrystals with an increase of the shell thickness from 0.5 to 3.4 monolayers have been studied by resonant Raman spectroscopy. The results show that at a thickness of about 2ML the surface of the CdSe core is mainly defect free although the structure of the shell is not established yet. The latter occurs at the thickness more than 3.4 ML where the shell is, most likely, amorphous. It is concluded that the defect-free core/shell interface is more important for producing high-luminescence QD structures than the increase of the shell thickness. 

The luminescence quenching for CdSe/ZnS nanocrystals passivated by organic ligands (pyridyl-substituted porphyrins, pyridine, 2,2 -bipyridine, 1,10-phenathroline) has been studied on the basis of steady-state and time resolved measurements in toluene at 295 K. The porphyrin Jt-conjugated macrocycle plays the principal role in non-radiative exciton relaxation in NC-organic ligand composites (via mesomeric effects and possible partial HOMO and LUMO overlap of porphyrin and meso-pyridyl rings). 

A luminescence of quantum size core-shell CdSe/ZnS nanocrystals solubilized with hydrophilic organic mercaptocompounds was studied. The long-chain molecules of mercaptoundecanoic acid effectively protect the surface of CdSe/ZnS nanocrystals, promote a high luminescence output and photostability of nanocrystals in contrast to short-chain molecules of mercaptoacetic acid. 

Three equimolar solutions of 4 nm CdSe/ZnS nanocrystals were prepared original nanocrystals dissolved in chloroform as a reference and water solutions with CdSe/ZnS nanocrystals solubilized with mercaptoacetic and mercaptoundecanoic acids. The solutions were illuminated with cw green laser (X=532 nm, P=0.5 W/cm2) and the PL spectra were recordered at certain time intervals. Fig. 2 shows the spectra of all examined solutions before and after prolonged laser irradiation. 

Figure 3. PL decay curves for CdSe/ZnS nanocrystals water solubilized with mercaptoacetic (a) and mercaptoundecanoic (b) acids irradiated with cw laser (X=532 nm, P=0.5 W/cm2).

Wang H, Nakamura H, Uehara M, Yamaguchi Y, Miyazaki M, Maeda H (2005) Highly luminescent CdSe/ZnS nanocrystals synthesized by a single molecular ZnS source in a microfluidic reactor. Adv Fund Mater 15 603-608... 

Preparation of TpEncapsulated CdSe/ZnS Nanocrystals via TOPO Ligand Displacement. 

Potapova I, Mruk R, Hiibner C, Zentel R, Basche T, Mews A (2005) CdSe/ZnS nanocrystals with dye-fimctionalised multi-anchor polymer-ligands. Angew Chtanie 44 2437... 

Schmitt F (2010) Temperature induced conformational changes in hybrid complexes formed from CdSe/ZnS nanocrystals and the phycobiliprotein antenna of Acaryochloris marina. J Opt 12(8) 84008... 

Schmitt F, Maksimov E, Suedmeyer H, Jeyasangar V, Theiss C, Paschenko V, Eichler H, Renger G (2011) Time resolved temperature switchable excitation energy transfer processes between CdSe/ZnS nanocrystals and phycobiliprotein anteima from Acaryochloris marina. Photonic Nanostruct 9(2) 190... 

The charge doping scheme of Guyot-Sionnest has been extended to CdSe-ZnS nanocrystals [529,530]. It is suggested that by proper tuning of the core... 

F. Q. Chen and D. Gerion, Fluorescent CdSe/ZnS nanocrystal-peptide conjugates for long-term, nontoxic imaging and nuclear targeting in living cells. Nano Letters, 4(10), 1827-1832 (2004). 

F. Pinaud et ah. Bioactivation and cell targeting of semiconductor CdSe/ZnS nanocrystals with phytochelatin-related peptides. Journal of the American Chemical Society, 126(19), 6115-6123 (2004). 

The active layer of three of these devices contained orange-emitting iridium(III) triplet emitter and green-emitting Au-CdSe/ZnS nanocrystals in the molar ratios... 

Recently, the synthesis of polymer nanocomposite OLEDs based on a new series of sulfide-containing polyfluorene homopolymers and copolymers and CdSe/ZnS nanocrystals was described by Yang et al. [38]. CdSe/ZnS nanoparticles were grafted to sulfur atoms by a ligand-exchanging reaction. The EL efficiency of nanocomposite OLEDs was effectively improved by QD nanocrystals incorporated in the polymers [38]. 

Another synthetic method for submicrometer fluorescence CdSe/ZnS/PS nanocomposite particles was developed by Joumaa et al. [205]. Submicrometersized particles were synthesized via a mini-emulsion PS process and CdSe/ZnS was coated by PS. Styrene emulsion and mini-emulsion polymerizations were performed in the presence of either TOPO-coated or vinyl-fimctionalized CdSe/ZnS nanocrystals. Both emulsion and mini-emulsion processes were first applied to the incorporation of TOPO-coated CdSe/ZnS nanoparticles. Then, the concentration and type of QD as well as the surfactant concentration were varied in order to investigate the influence of these parameters on the mini-emulsion polymerization kinetics and PL properties of the final particles. The final particle size could be tuned between 100 and 350 nm by varying the initial surfactant concentration. The intensity of luminescence properties increased with the number of incorporated TOPO-coated CdSe/ZnS nanoparticles, and the slight red shift of the emission maximum, induced by the polymerization, was correlated with modification of the medium surrounding the nanoparticles. TOPO-coated CdSe/ZnS nanoparticles showed higher fluorescence intensity than those with a vinyl moiety [205]. 

Jasieniak, J., Pacifico, J Signorini, R Chiasera, A Ferrari, M Martucci, A., and Mulvaney, P. (2007) Luminescence and amplified stimulated emission in CdSe-ZnS-nanocrystal-doped Ti02 and Zr02 waveguides. Adv. Fund. Mater., 17, 1654-1662. 

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