CdSe quantum dots

Electroluminescence from CdSe quantum dot / polymer composite. App/. Phys. Lett, 66,1316-1318. 

The fundamental issue of epitaxial growth on polycrystalline substrates has been addressed in a more refined manner in relation to the electrodeposition of CdSe on metals. Polycrystalline, lll -textured Au surfaces were shown [17] to promote the electrodeposition of coherent, epitaxial CdSe quantum dot films over areas micrometers in size, i.e., much larger than the polycrystalline Au grains, despite the numerous grain boundaries present in the substrate. The Au films (considered as... 

Ruach-Nir I, Wagner HD, Rubinstein I, Hodes G (2003) Structural effects in the electrodeposition of CdSe quantum dots on mechanically strained gold. Adv Eunct Mater 13 159-164... 

Fig. 5.19 (a) Linking CdSe quantum dots to Ti02 particle with bifunctional surface modifier (b) light harvesting assembly composed of T102 film functionahzed with CdSe Q-dots on optically transparent electrode (OTE). [Adapted (in gray scale) from [348]]... 

Fig. 5.20 Schematic diagram illustrating the energy levels of different-sized CdSe quantum dots and Ti02 (band positions are not drawn to scale). The injection of electrons from CdSe into Ti02 is influenced by the energy difference between the two conduction bands. [Adapted (in gray scale) from [351]]...

Toyoda T, Tsuboya 1, Shen Q (2005) Effect of rutile-type content on nanostructured anatase-type Ti02 electrode sensitized with CdSe quantum dots characterized with photoacoustic and photoelectrochemical current spectroscopies. Mater Sci Eng C 25 853-857... 

Toyoda T, Kobayashi J, Shen Q (2008) Correlation between crystal growth and photosensitization of nanostructured HO2 electrodes using supporting H substrates by self-assembled CdSe quantum dots. Thin SoUd Films 516 2426-2431... 

Shen Q, Arae D, Toyoda T (2004) Photosensitization of nanostructured TiOa with CdSe quantum dots effects of microstructure and electron transport in HO2 substrates. J Photoch Photobio A 164 75-80... 

Nonexponential blinking kinetics of single CdSe quantum dots A universal power law behavior. J. Chem. Phys., 112, 3117-3120. 

Issac, A., Borczyskowski, C. V. and Cichos, F. (2005) Correlation between photoluminescence intermittency of CdSe quantum dots and self-trapped states in dielectric media. Phys. Rev. B, 71, 161302 (R)-l-161302(R)-4. 

Yamaoka, Y, Yokoyama, H., Baba, Y. and Ishikawa, M. (2005) Subsecond luminescence intensity fluctuations of single CdSe quantum dots. J. Phys. Chem. B, 109, 14350-14355. 

Photoluminescence of CdSe Quantum Dots Shifting, Enhancement and Blinking... 

Figure 17.1 (A) S ize-dependent photoluminescence colorofZnS-shelled CdSe quantum dots. (B) Schematic presentation of size in A, color, and photoluminescence spectral maxima of CdSe quantum dots. (C) Size-dependent absorption (solid lines) and photoluminescence (broken lines) spectra of CdSe quantum dots. Reprinted with permission from references [4] (A) and [5] (C) copyright [1997, 2001], American Chemical Society.

This chapter presents an overview of the synthesis, ensemble photoluminescence properties and blinking of single CdSe quantum dots. The stress is on (i) widely accepted methods of synthesis, (ii) the origin of photoluminescence and variations of photoluminescence as functions of surface-coating, surface-passivating molecules, chemical environment, and thermal- and photo-activations, and (iii) photolumines-... 

In the 1980s, CdSe quantum dots vere prepared by top-dovm techniques such as lithography ho vever, size variations, crystal defects, poor reproducibility, and poor optical properties of quantum dots made them inadequate for advanced applications. Introduction of bottom-up colloidal synthesis of CdSe quantum dots by Murray et al. [3] and its further advancements brought radical changes in the properties of quantum dots and their applications in devices and biology. The colloidal syntheses of CdSe quantum dots are broadly classified into organic-phase synthesis and aqueous-phase synthesis. 

Synthesis of CdSe Quantum Dots in Organic Phases... 

Although direct synthesis of cadmium chalcogenide quantum dots in the aqueous phase was achieved nearly 30 years ago, the synthesis of size-controlled CdSe quantum dots in the aqueous phase became possible only recently. Rogach et al. successfully synthesized CdSe quantum dots in the aqueous phase from a mixture of cadmium perchlorate (4.7 mmol), sodium hydroselenide (2.2 mmol), and 2-mercaptoethanol or 1-thioglycerol (11.54mmol) [15]. In a typical synthesis, the above mixture was refluxed in an aqueous NaOH solution (pH = 11.2) in a N2... 

Figure 17.2 (A) Absorption and photoluminescence spectra of CdSe quantum dots prepared from CdO, CdC03, and Cd(AcO)2 in the presence of different ligands. (B) Increase in the optical density (at 400 nm) of a CdSe quantum dot reaction mixture with time under reaction at 75 "C. Color pictures in the inset of B represent CdSe (a,b) andCdSe-ZnS (c) quantum...

In addition to the photoluminescence red shifts, broadening of photoluminescence spectra and decrease in the photoluminescence quantum efficiency are reported with increasing temperature. The spectral broadening is due to scattering by coupling of excitons with acoustic and LO phonons [22]. The decrease in the photoluminescence quantum efficiency is due to non-radiative relaxation from the thermally activated state. The Stark effect also produces photoluminescence spectral shifts in CdSe quantum dots [23]. Large red shifts up to 75 meV are reported in the photoluminescence spectra of CdSe quantum dots under an applied electric field of 350 kVcm . Here, the applied electric field decreases or cancels a component in the excited state dipole that is parallel to the applied field the excited state dipole is contributed by the charge carriers present on the surface of the quantum dots. 

Figure 17.4 (A) Photoluminescence spectral shifts (AX,) of a solution of CdSe quantum dot aggregates during heating-cooling cycles photoluminescence spectral maxima were recorded at 298 K during cooling and 353 K during heating. Reversibility of the photoluminescence spectral shift was attained after four heating-cooling cycles. (B) Photoluminescence spectra of a solution ofCdSe...

Figure 7.5 Schematic presentation of photoactivation and relaxation processes in a CdSe quantum dot aggregate (a) surface-passivation of photoexcited quantum dots by solvent molecules or dissolved oxygen, (b) thermal activation followed by the formation ofa stabilized state, (c) the formation of deep-trap states, (d) non-radiative relaxation of deep-...

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