Latent radical image

Figure 15 Top Photographic latent image formation in undoped (left) and formate-doped and gold-sulfide sensitized AgBr crystals with the hole-scavenging step (center). Secondary reduction step by formyl radical (right). Bottom Sensitometry curves for gold-sulfide sensitized emulsions, undoped or formate-doped, and developed after 5 or 20 min (texp = 10 sec, development with aminophenol and ascorbic acid). The same absorbance is observed for a number of photons absorbed 5 or 10 times less, respectively, than in the undoped emulsion. (From Ref. 200.)...

The assumption that some dyes can spectrally sensitize latent image formation in silver halides by direct electron transfer from the excited dye to the conduction band and other dyes by indirect electron transfer from the dye radical formed by photoinjection of a hole into the valence band is in good accord with experiment. The locations of the highest filled and lowest vacant energy levels of the dye relative to the valence and conduction bands of the silver halide determine which mode of sensitization will occur, or whether both can occur. 

Figures 49(c) and 49(d) show two other important processes which can occur when the silver halide is excited directly in the presence of adsorbed dyes. In these cases an electron is transferred from the VB to the CB upon excitation, and the holes in the VB may be filled by electron transfer from the HOMO of the adsorbed dye. The product of this process in Figure 49(c) is the same as that from the electron-injection dye sensitization in Figure 49(a), i.e., a dye radical cation and a conduction band electron which may be trapped and contribute to latent image formation. Illustrated in Figure 49(d) is the consequence of excitation of silver halide in the presence of a dye in which the energy of the LUMO is lower than that of the CB. In this case, direct excitation of the silver halide results in a conduction band electron which can be transferred to the LUMO of the dye. Subsequent electron transfer of an electron from the HOMO of what would then be a dye radical anion results in effective deactivation of the band-gap excitation, and overall reduced photographic sensitivity of the silver halide toward direct excitation due to the presence of the dye. This process is known as dye desensitization.

The idea being a basis for the method is simply to use a radical or ion latent image formed after selective exposure of a photosensitive layer to initiate graft-polymerization of monomers containing silicon and/or of... 

Figure 11 Photographic latent image formation in undoped and formate-doped and gold-sulfide (S) sensitized AgBr crystals. Top undoped crystal with electron-hole recombination. Centre formate doped crystal and hole scavenging step by formate (HCOp). Bottom formate-doped crystal and delayed reduction step of additional silver ions by carboxyl radicals CO- [16],...

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