CdTe quantum dots

Relaxation Dynamics of Non-Emissive State for Water-Soluble CdTe Quantum Dots 147 8.4... 

In spite of the potential advantage, however, only a handful studies on quantum dots by PCS have been published up to now, for CdSe [20-23] and for CdTe [24]. In the following, the results of PCS measurement for CdTe quantum dots in water will be presented and the time scale of the off time will be characterized on the basis of the autocorrelation function obtained. 

Non-Emissive Relaxation Dynamics in CdTe Quantum dots... 

Figure 8.11a shows steady-state absorption spectra of the CdTe quantum dots in water. Each spectrum in the figure exhibits a distinct peak at a different band corresponding to its size, indicating that all of these suspensions include mono-dispersed nanocrystals. This mono-dispersibility is also supported by their emission spectra with different peak bands corresponding to particle size, as in Figure 8.11b. 

Figure 8.11 Absorption (a) and emission (b) spectra for the water-soluble CdTe quantum dots examined. The sizes for the CdTe dots are indicated in the figures.

Figure 8.12 Typical fluorescence autocorrelation curve (gray closed circles) of the CdTe quantum dots with 4.6 nm diameter in water with a calculated curve (solid line) based on Eq. (8.1) (a) and based on Eq. (8.3) (b). Residuals are also indicated at the top of each trace.

Figure 8.13 Autocorrelation curves for the CdTe quantum dots with diameter 4.9 nm at the excitation laser power from 10-200 XW (a). Comparison of the shapes of these autocorrelation curves by normalization (b).

Figure 8.14 (a) Values of as a function of corresponding diffusion times (observation times) for each CdTe quantum dot. Four sets of measurements for one sample were conducted with diferent sized pinholes and different solvent as follows (1) 25 Xm pinhole, in water (2) 25 Xm pinhole, in deuterated water (3) 50 Xm pinhole. 

Nonlinear Optical Properties and Single Particle Spectroscopy of CdTe Quantum Dots... 

Pan, L., Tamai, N., Kamada, K. and Deki, S. (2007) Nonlinear optical properties of thiol-capped CdTe quantum dots in nonresonant region. Appl. Phys. Lett., 91, 051902-1-051902-3. 

Pan, L., Ishikawa, A. and Tamai, N. (2007) Detection of optical trapping of CdTe quantum dots by two-photon-induced luminescence. Phys. Rev. B, 75, 161305R-1-161305R-4. 

Mandal, A., Nakayama, J., Tamai, N., Biju, V. and Isikawa, M. (2007) Optical and dynamic properties of water-soluble highly luminescent CdTe quantum dots. J. Phys. Chem. B, 111, 12765-12771 Mandal, A. and Tamai, N. (2008) Influence of acid on luminescence properties of thioglycolic acid-capped CdTe quantum dots. J. Phys. Chem. C, 112, 8244-8250. 

Ma J, Chen J, Guo J, Wang CC, Yang WL, Xu L, Wang PN (2006) Photostability of thiol-capped CdTe quantum dots in living cells the effect of photo-oxidation. Nanotechnology 17 2083-2089... 

Anodic Stripping Voltammetry of Anti-VI Antibody Functionalized CdTe Quantum Dots for Specific Monitoring of Salmonella enterica serovar Typhi... 

Depending on the kind of synthesis, these quantum dots can be prepared or size separated into batches covering almost the entire visible spectral range from 400 to 750 nm with, in part, high photoluminescence quantum efficiencies (some stable in air [106], others not [107]). Weller et al. reported on a very efficient synthesis for hydrophilic, thiol-capped CdTe quantum dots [108,109], which can be transformed to lipophilic, alkanethiol-stabilized CdTe quantum dots using a place exchange reaction similar to that for metal nanoparticles described above [110]. A related strategy has also been successfully employed to produce hydrophobic or otherwise functionalized CdS [111] or CdSe quantum dots [112] (Fig. 1). 

Our group also reported on mixtures of a nematic 2-phenyl-pyrimidine derivative (Felix-2900-03) containing either hexadecylamine-capped CdSe (ranging in size from 2.5 to 5.2 nm) or thioglycolic acid-capped CdTe quantum dots (3.2-4.0 nm in... 

Wang, Q., Kuo, Y., Wang, Y., Shin, G., Ruengraglikit, C., and Fluang, Q. (2006). Luminescent properties of water-soluble denatured BSA-coated CdTe quantum dots. J. Phys. Chem. B,... 

Komarala, V. K., Rakovich, Y. P., Bradley, A. L., Byrne, S. J, Gun ko, Y. K., Gaponik, N. and Eychmuller, A. (2006). Off-resonance surface plasmon enhanced spontaneous emission from CdTe quantum dots. Appl. Phys. Lett. 89 253118. 

Figure fO.2 compares the optical properties and hydrodynamic sizes of CdTe quantum dots (2.5 nm) coated with a traditional amphiphilic pol3mier (octylamine-modihed polyacrylic acid) or the mixed thiol/amine multidentate ligand. Although the amphiphilic pol3mier and the multidenate ligand were prepared from the same molecular-weight polyacrylic acid backbone, the... 

Fig. 10.2. Comparison of optical and hydrodynamic properties of CdTe quantum dots (2.5 nm) solubilized in water with an amphiphilic polymer (octylamine-modified polyacrylic acid) or a multidentate polymer ligand, (a) Absorption (blue curves) and fluorescence emission red curves) spectra of CdTe quantum dots with amphiphilic polymer upper) or multidentate polymer lower) coatings, (b) Dynamic light scattering size data of quantum dots with amphiphilic polymer blue curve) and multidentate polymer green curve) coatings. PL Photoluminescence, AU Arbitrary units. All samples were dissolved in phosphate buffered saline...

Fig. 10.3. Effects of polymer capping ratios on quantum dot properties, (a) Fluorescence quantum yield blue curve) and polydispersity index red curve) of 2.5 nm CdTe quantum dots as a function of molar capping ratio. Polydispersity indices were calculated from gel filtration chromatograms, (b) Photostability data at various capping ratios (MCR = 1.5, 1.0, or 0.5) and in the absence of polymer (MCR = 0)...

CdTe quantum dots, resulting in polydisperse nanocrystals. Polydispersity was quantitatively assessed from the polydispersity index (PDI) in gel filtration chromatograms. When the MCR values are above 2.0, the excess polymer leads to better monodispersity and colloidal stability, but a reduced fluorescence quantum yield. Between these two limits is the optimal capping ratio (OCR) of approximately 1.5, yielding small, monodisperse nanocrystals (PDI < 1.5) with bright fluorescence ( 50% quantum yield) and exceptional photostability. 

Fig. 10.4. (a) Gel filtration chromatograms of multidentate polymer coated CdTe quantum dots showing direct size comparison with protein standards ferritin (440 kDa), aldolase (158 kDa), ovalbumin (43kDa), and carbonic anhydrase (29kDa). (b) Fluorescence emission spectra from the corresponding quantum dots. The quantum dot hydrodynamic sizes are 5.6 nm (2.5 nm core, blue), 6.6 nm (3.1 nm core, green), 7.8nm (4.0nm core, red), and 9.7nm (6.0nm core, brown)... 

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