Optical Properties of Quantum Dots

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. 

Electronic and Optical Properties of Quantum Dots, 563 Type I and Type II Core-Shell Quantum Dots, 565 The Absorption Cross-Sections of Quantum Dots, 565 Absorption and Emission Maxima of Quantum Dots, 567 Luminescence Lifetimes of Q-Dots, 567 Electrochemistry of Nanoparticles, 569 Conclusion, 571 Further Reading, 571 References, 572 Problems, 575 Answers, 576... 

Quantum dots are semiconductors composed of atoms from groups II-VI or III-V elements of the periodic table, for example, CdSe, CdTe, and InP (39). Their brightness is attributed to the quantization of energy levels due to confinement of an eleetron in a three-dimensional box. The optical properties of quantum dots can be manipulated by synthesizing a (usually stabilizing) shell. Such Q-dots are known as core-shell quantum dots, for example, CdSe-ZnS, InP-ZnS, and InP-CdSe. In this section, we will discuss the different properties of quantum dots based on their size and composition. 

The optical properties of quantum dots have been extensively investigated. They have discrete atomic-like energy levels that alter predictably as the size of the particle changes, so that the light emitted can be tuned. This finds application in many areas, including displays and lasers. 

Optical Properties of Quantum Dot Nano-composite Materials Studied by Solid-State Theory Calculations... 

With advances in nanotechnology, quantum dots are ubiquitous in surfaces with myriad applications in electrochemistry. In this chapter, we discuss the numerical modelling of quantum dots both the spherically symmetric (metal or semiconductor) dots embedded in a matrix (usually a dielectric) and the hemispherical metal dots (a.k.a. nanoparticles or thin-film islands) supported by a substrate (again, usually a dielectric). We are particularly concerned about the optical properties of quantum dots, since the interaction of light with quantum dots is used widely for several applications in surface electrochemistry - from characterization of the thickness and quality of thin films, to the development of surface sensors - as well as in nanoelectronics and quantum computing. 

Before discussing the experimental evidence, it is worthwhile to consider lasing-related properties of quantum dots from a fundamental point of view. The theoretical description of the optical gain in bulk and quantum well semiconductors is discussed in Datareview C5.3. 

Optical Properties of PDA Microcrystals of Different Sizes. The effect of average molecular weight on the functions of PDA microcrystals is expected to be important from the point of view that the electronic and nonlinear optical properties of quantum-wire and quantum-dot structures differ significantly from those of bulk crystals. An enhancement of several orders of magnitude in third-order optical nonlinearities has been predicted in the case of quantized microaystallites. 

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. 

Owing to their unique (tunable-electronic) properties, semiconductor (quantum dots) nanocrystals have generated considerable interest for optical DNA detection [12], Recent activity has demonstrated the utility of quantum dot nanoparticles for enhanced electrical DNA detection [33, 34, 50], Willner et al. reported on a photoelectrochemical transduction of DNA sensing events in connection with DNA cross-linked CdS nanoparticle arrays [50], The electrostatic binding of the Ru(NH3)63+ electron acceptor to the dsDNA... 

Leem, J.-Y., Jeon, M., Lee, J. el al. (2003) Influence of GaAs/InAs quasi-monolayer on the structural and optical properties of InAs/GaAs quantum dots. Journal of Crystal Growth, 252(4), 493-98. 

The size-dependent properties of nanoparticles differ greatly from the corresponding bulk materials. An example is the size quantization phenomenon commonly observed in II-VI and III-V inorganic semiconductor nanocrystals.6 During the intermediate transition towards that of the bulk metal (usually between 2 and 20 nm), localization of electrons and holes in a confined volume causes an increase in its effective optical band gap as the size of the nanoparticle decreases, observed as a blue shift in its optical spectrum. Bms predicted that there should also be a dependence on the redox potential for these same classes of quantum dots.7 Bard and coworkers showed this experimentally and have reported on the direct observation between the... 

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