Exiton states

Gleiter, 2000 Valiev, 2002). In this case, the delocalized wave function associated with an exitonic state (i.e., a band gap transition to the lowest states in the conduction band) may be restricted in its extent at small diameters, thus raising its energy relative to the bulk state (Kayanuma, 1988). However, the increase in reactivity which is frequently associated with nanosized particles caimot generally be related to quantum confinement (QC) (Waychunas and Zhang, 2008) but is, in many cases (if not in most cases) due to surface-state modifications and structural disorders. 

The reduction of the inhomogeneous linewidth follows from Van Vleck s calculation of the second moment (AB ). It states that (AB > is proportional to N is here the number of nuclear spins. In an A - B pair, the number of nuclear spins is doubled in comparison to an isolated molecule. Therefore, the inhomogeneous linewidth is reduced by the factor 1 /-/z. The experimental values in naphthalene confirm this interpretation in the immediate neighbourhood of the A-M - B crossing points (a = 120° in Fig. 7.4), the experimental value for the ratio of the linewidths of the mini-exitons to those of the isolated molecules is ABm/ABab = 1/1.6. The width AB is thus an additional confirmation of the model for a mini-exciton it consists of the two molecules in a unit cell. At higher N-hg concentrations x = 10%), A-A-B and A-B-B mini-excitons have also been observed [4]. 

One of the strategies is to minimize the diffusion path of exitons (botmd states between an electron and electron hole) generated by photons hitting the active material in a photovoltaic cell. Once separated, holes and electrons should reach anode and cathode electrodes, respectively. During the process, recombination of holes and electrons lead to energy losses via thermal dissipation. In order to reduce such losses, minimizing the diffusion paths of exitons by means of BCP-derived nanostructures may be beneficial. To this end, a thin solid-state dye-sensitized solar cell (ssDSSC) with a 3D gyroidal titania network was fabricated (see Fig. 12) [37]. In contrast to typical disordered nanoparticle networks, the ordered mesoporous... 

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