Temperature electronic excitation onset

The detection of sharp plasmon absorption signifies the onset of metallic character. This phenomenon occurs in the presence of a conduction band intersected by the Fermi level, which enables electron-hole pairs of all energies, no matter how small, to be excited. A metal, of course, conducts current electrically and its resistivity has a positive temperature coefficient. On the basis of these definitions, aqueous 5-10 nm colloidal silver particles, in the millimolar concentration range, can be considered to be metallic. Smaller particles in the 100-A > D > 20-A size domain, which exhibit absorption spectra blue-shifted from the plasmon band (Fig. 80), have been suggested to be quasi-metallic [513] these particles are size-quantized [8-11]. Still smaller particles, having distinct absorption bands in the ultraviolet region, are non-metallic silver clusters. 

Establishment of the mechanism and practical applications of excited state energy- and electron transfer processes require precise information on the energies and redox potentials for oxidation and reduction processes in the ground and excited state. Onset of the luminescence is a direct way of determining the excited state energies. Due to possible solvent-induced excited state relaxation effects that can occur at ambient temperature. 

Figure 20 (a-c) Drift and diffusion of optically excited carriers in P-rhombohedral boron. Densities of electrons, electron-bole pairs, and boles at different distances from tbe illuminated surface versus transit time related to the onset of steady-state optical excitation (112). (d) Temperature dependence of the hole drift mobility in P-rhombohedral boron derived from transient photoconduction (113). 

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