Quantum dots electron absorption spectroscopy

A complete and satisfactory characterization of quantum dots prepared by any of these methods requires many of the same techniques listed for metal nanoparticles described already (see above). In addition to critical electronic properties, photoluminescence spectroscopy is an extremely valuable tool to obtain preliminary information on size and size distribution of quantum dots, which can in many cases (i.e., for larger sizes and quasi-spherical shapes) be estimated from 2max and the full width at half maximum (fwhm) of the absorption or emission peak using approximations such as Bras model or the hyperbolic band model [113]. 

Systematic size induced changes in the electronic structure of QDs have been extensively studied in the last decade. Sustained efforts have established interesting applications based on the blue-shift of the absorption edge due to the quantum confinement in nanometer-sized samples. Absorption spectroscopy is one of the simplest technique that has been employed to study the electronic structure of nanocrystals. Upon irradiation with light of energy greater than the band gap, NCs are known to absorb photons and promote electrons from the valence band (VB) to the conduction band (CB). The onset of the absorption spectrum generally corresponds to the band gap of QDs. The band gap is size tunable and decreases very sensitively with increase in the size of the dot. This relationship is shown in Fig. 2a for a typical system like the ZnO QDs. This size dependence... 

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