Vacancy clusters spectra

Figure 4 shows the present theoretical spectra and the experimental spectra (25). In the theoretical spectrum for the vacancy-containing cluster, the peaks A-C appear as well as for Ce02- The peak A becomes blurred because the resonances among the oxygen atoms are weakened due to the oxygen defect. The part for the peak A was not reported for the experimental spectrum. 

Note that in LRC, the stable Frenkel pairs may be formed (e.g., under irradiation). The energy spectrum of Frenkel pair formation is somewhat spread due to the spread in energies of vacancies and interstitials formation. The width of this spectrum as well as variations in energy of vacancies and interstitials formation may amount to some eV, and the typical values of the threshold energy of Frenkel pair formation in metallic glasses as well as in crystals may amount to about 25-30 eV. To point defects of a cluster one may attribute also the interstitial and substitutional impurities that locally break the topological and compositional order. 

Almost all of the semiconductor clusters prepared so far show red-shifted broad band luminescence (e.g., Figure 13). These luminescences cannot be attributed to states that are populated directly by optical absorption. Rather, they are usually associated with defects such as vacancies, interstitials, impurities, and so on (Figure 10). These defect states have low oscillator strength and therefore are not observable in the absorption spectrum. Very few definitive facts are known about the nature of these defects, except that they are located mostly on the surfaces of the cluster. 

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