Luminescence defect

Another open question is the relationship between the H-induced radiative recombination centers and the H-induced platelets. Controlled layer removal of the plasma-processed silicon surface reveals that the density of luminescence centers decays nearly exponentially with a decay length that is comparable to the depth over which the platelets form (Northrop and Oehrlein, 1986 Jeng et al., 1988 Johnson et al., 1987a). However, the defect luminescence has also been obtained from reactive-ion etched specimens in which platelets were undetectable (Wu et al., 1988). Finally, substantial changes in the luminescence spectra occur at anneal temperatures as low as 250°C (Singh et al., 1989), while higher temperatures... 

Finally, we have measured the time-dependent behavior of the PL spectra at 77 K. At a delay time of 0-2 ns we observed strong UV PL (Fig. 7). At steady state conditions a deep-level yellow-red emission coimected with defect luminescence is observed. So it could be concluded that exciton recombination is a faster process than recombination via deep levels. 

The luminescence intensity can also be enhanced by the addition of foreign molecules to the cluster surfaces. Treatment of CdS clusters with triethylamine [71] and lanthanide /J-diketone complexes [75] can enhance the intensity of the defect luminescence. Inorganics such as silver sulfide [67], silver perchlorate [67], and cadmium hydroxide [35] have been used to activate the luminescence of CdS colloids. The exact mechanisms of luminescence enhancement are not well understood. 

Surface defects such as dangling bonds and vacancies may, in principle, be removed by chemical passivation techniques. A successful passivation procedure should result in the disappearance of defect luminescence and the appearance of strong exciton luminescence. Many chemicals have been tried for this purpose but with few successes. The two most successful passivation techniques developed so far involve the use of ammonia [50] and hydroxide ion [35]. In both cases, defect luminescence is greatly reduced with the... 

The optical spectra of Al203-based materials have been studied extensively since the late 1950s. In the presence of lattice defects, luminescence emission, related to oxygen vacancies, can be observed in Al203-based materials using the cathodoluminescence technique [17], Typical spectra... 

Fig. 6.13 a Self-trapped exciton emission, b oxygen-vacaney defect luminescence, and c recombination process between the conduction electron and the excited holes. Adapted from Ref. [55] by permission of Macmillan Publishers Ltd. 

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