Optical Characteristics of the Silicon-Centered PCs

In this section, the experimental data on the optical absorption spectra of the structurally different silicon-centered PCs stabilized at the surface of quartz glass are reported (see also Ref. [56]), and the question of the possible 

in the electronically excited state, the dissociation of the silyl radical is possible which is accompanied by the elimination of one of the substitutes of three-coordinated Si atom (in this case, the H atom). These results agree with the results of the quantum-chemical study of photo conversion of the H3Si radicals [60]. In this work it was shown that low-lying electronically excited terms of this radical are dissociation terms, and their relaxation is accompanied by elimination of the H atom. 

Low-molecular radicals OH and H were also detected under UV-irradiation of the surface (=Si-0)2Si -0H radicals (our unpublished data). Thus, in this case the decomposition with the production of the low-molecular radical is also typical for the electronically excited state of the 

In the (=Si-0)2Si -0H radical, the a-Si atom is already bonded with three oxygen atoms and this PC is chemically similar to the E y-center. 

In both examples considered it was only possible to detect the primary products of photo decay of the surface defects because they represented low-molecular radicals and could easily leave the place of their birth and can be trapped by especially chosen acceptors. 

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