Cds nanocrystals

Tittel J, Gdhde W, Koberling F, Basche T, Kornowski A, Weller H and Eychmuller A 1997 Fluorescence spectroscopy on single CdS nanocrystals J. Chem. Phys. B 101 3013-16... 

Goldstein A N, Colvin V L and Alivisatos A P 1991 Qbservation of melting in 30 angstrom diameter CdS nanocrystals Mater. Res. Soc. Symp. Proc. 206 271... 

Korgel, B. A. and Monbouquette, H. G. (1996). Synthesis of Size-Monodisperse CdS Nanocrystals Using Phosphatidylcholine Vesicles as True Reaction Compartments. /. Phys. Chem., 100, 346-351. 

Fig, 3. TEM images of (a) ZnS nanociystals, (b) CdS nanocrystals, (c) cube-shaped PbS nanocrystals, (d) hexagon-shaped MnS nanocrystals. 

Peng ZA, Peng XG (2001) Eormation of high-quahty CdTe, CdSe, and CdS nanocrystals using CdO as precursor. J Am Chem Soc 123 183-184... 

On the other hand, the nonlinear optical properties of nanometer-sized materials are also known to be different from the bulk, and such properties are strongly dependent on size and shape [11]. In 1992, Wang and Herron reported that the third-order nonlinear susceptibility, of silicon nanocrystals increased with decreasing size [12]. In contrast to silicon nanocrystals, of CdS nanocrystals decreased with decreasing size [ 13 ]. These results stimulated the investigation of the nonlinear optical properties of other semiconductor QDs. For the CdTe QDs that we are concentrating on, there have been few studies of nonresonant third-order nonlinear parameters. 

Jian D, Gao Q (2006) Synthesis of CdS nanocrystals and Au/CdS nanocomposites through ultrasound activation liquid-liquid two-phase approach at room temperature. Chem Eng J 121 9-16... 

Sone and Samuel (2004) continued the studies of mineralization on PA nanofibers by utilizing the same PA described above to nucleate and grow CdS nanocrystals. In this case, the negatively charged phosphate and carboxylate groups bind to Cd, and CdS was formed after diffusion of H2S gas. A low Cd to PA ratio led to the formation of CdS nanocrystals that were 3-5 nm in diameter. An intermediate ratio of... 

Fig. 6 Schematic diagram illustrating the three-step electrochemical/chemical expitaxial synthesis of CdS nanocrystals [154].

Photoelectrochemical characterization was also carried out on CdS films using different sizes of CdS nanocrystals [75]. Voe increased with decreasing crystal size from 0.58V (75 nm) to 0.68 V (5 nm). Surprisingly, he was not dependent... 

Figure 8. Kinetic evolution of CdS band-gap energy (A) and Co2+ ligand-field absorption intensity ( ), collected in situ during the synthesis of Co2+ CdS nanocrystals in inverted micelles.

Figure 9. (a) Co2+ ligand-field absorption spectra for as-prepared Co2+ CdS nanocrystals,... 

The solvation of transition metal ions bound to the surfaces of nanocrystals clearly relates to the thermodynamics of their interaction with the surface. It is interesting to note that Mn2+ solvation from CdSe nanocrystal surfaces appeared to be complete after a Py ligand-exchange procedure that took 24h (47), whereas Co2+ on the surfaces of CdS nanocrystals requires weeks to be solvated by Py (68), and Co2+ on the surfaces of ZnS nanocrystals was not solvated by Py to any measurable extent (91). The thermodynamic variations thus depend sensitively on the geometries of the surface-binding sites offered to the dopants. For example, the S S separations of CdS surfaces are apparently too large to stabilize Co2+ ions to the same extent as those of ZnS. As discussed in Section II.C, the capacity a surface has to stabilize bound dopants is intimately related to... 

An interesting approach recently applied to doped nanocrystals is the heterocrystalline core-shell method commonly applied to pure nanocrystals. In a series of papers (102, 103), Mn2+ CdS nanocrystals were synthesized in inverted micelles under conditions very similar to those described above and in Figs. 8, 9, and 13. The poor luminescent properties of the resulting Mn2+ CdS nanocrystals were attributed to nonradiative recombination at unpassivated CdS surface states. From the discussion in Section I and II.C, however, it is likely that a large fraction if not all of the Mn2+ ions resided on the surfaces of these as-prepared nanocrystals as observed for Co2+ (Fig. 9). This interpretation is supported by studies in other laboratories that showed large Mn2+ surface populations in Mn2+ CdS nanocrystals grown by the same inverted micelle approach (63). Nevertheless, growth of a ZnS shell around these Mn2+ CdS nanocrystals led to an approximately ninefold increase in Mn2+ 4T 1 > 6A i... 

Figure 17 X-ray powder diffraction patterns for core-shell nanocrystals. In panel (A) 4.0 nm diameter CdSe QDs overcoated with (a) 0, (b) 0.65, (c) 1.3, (d) 2.6, and (e) 5.3 monolayers of ZnS shell. The thin solid lines show simulations of the data. Powder patterns for wurtzite CdSe and ZnS are included for comparison in the botton and top insets, respectively. [Adapted from (95).] (B) 3.5 nm diameter pure CdS nanocrystals (dotted), 3.9 nm diameter CdSe nanocrystals (dashed), and core-shell samples having the same 3.9 nm CdSe core and CdS shell thicknesses of (a) 0.2 nm, (b) 0.7 nm, and (c) 1.1 nm. The dashed vertical lines represent peak positions for pure CdSe the solid lines represent pure CdS. [Adapted from (100).]...

The sensitivity of EPR to multiple coordination environments has been demonstrated in studies of Mn2+-doped CdS nanocrystals (63). In Mn2+ CdS nanocrystalline powders prepared by inverted micelle synthesis, four distinct resonances were observed and deconvoluted by varying experimental parameters including microwave power, microwave frequency, and temperature. The deconvoluted signals are shown in Fig. 18. Four distinct manganese species were detected through this experiment. A six line spectrum characteristic of isolated paramagnetic Mn2+ was observed at 300 K and below [multiline... 

Mn2+ CdS nanocrystals prepared by this method. A similar approach has been applied to colloidal Mn2+ -doped ZnSe nanocrystals (90) prepared via a singlesource precursor method (Section II.A), which showed evidence for both a disordered surface-bound or near-surface Mn2+ and an internal substitutional Mn2+. In both of these studies, this information was then applied in the analysis of energy-transfer processes involving the near-surface Mn2+ ions. 

The synthesis of Mn2+-doped CdS nanocrystals has been studied by several groups. In one such study (82), the doped CdS nanocrystals were prepared by simple mixing of ethylene glycol solutions of cadmium and manganese acetate with a solution of sodium sulfide, followed by washing with methanol and thermal treatment in triethyl phosphate to deagglomerate the particles. Mean... 

Figure 25. Excitation and photoluminescence (solid and dashed lines) of x% Mn2+ CdS nanocrystals, where. v = 0 (a), 0.8 (fe), 2.5 (c), and 4.8 (d). The solid luminescence spectra were collected in CW mode, and the dashed luminescence spectra were collected with a pulsed excitation source and a 2-ms delay between excitation and emission detection. Note that the intensities of (b)-(d) are referenced to that of (a). [Adapted from (82).]...

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