We have studied characteristic features of photoinduced processes occurring in CdSe/ZnS semiconductor nanocrystals on prolonged exposure to ultraviolet light in air and under vacuum. Accelerated photodegradation of the nanocrystals in air has been established, associated with photooxidation.Introduction. Cadmium selenide semiconductor nanocrystals are a fluorescent material with unique optical properties. Their optical parameters, including the spectral position of the luminescence band, are tuned by varying the particle size from 2 to 10 nm, due to quantum size effects. The luminescence spectrum of the nanocrystals is a relatively narrow band, the position of the maximum in which depends on the average size of the nanocrystals, while the width is determined by the spread in their sizes. Modern synthesize techniques allow us to obtain nanocrystals with ≤5-10% spread in size, and as a result the luminescence band is significantly narrower than in most luminescent organic molecules.The methods developed for synthesis of core/shell type nanocrystals [1-3] make it possible to obtain nanostructures with high luminescence quantum yield, as a result of the fact that an energy barrier is created for electronhole pairs that prevents nonradiative exchange of energy with the external environment. Thus semiconductor nanocrystals are a promising alternative to conventional luminophores based on organic dyes, and may be used to design optoelectronic devices. However, their performance is determined by the stability of the luminescent characteristics, including under prolonged UV irradiation.In [4], it is shown that when bulk single-crystal CdS, ZnS, ZnSe semiconductors are exposed to UV radiation, the luminescence intensity decreases as a result of photodegradation of the surface layer, the rate of which depends on the power density, the exposure time, the environment, the mechanical condition of the surface, and the temperature. The photodegradation processes are explained by the occurrence of anode reactions involving nonequilibrium holes, localized on lattice defects in the near-surface layer.In [5][6][7][8], a number of effects are considered that are connected with the change in luminescence characteristics when cadmium chalcogenides are exposed to prolonged UV irradiation (photo-induced sudden rise in luminescence intensity, quenching of luminescence, oscillations in photoluminescence) and models were proposed to explain these effects. It was shown that degradation of the nanocrystals during irradiation is expressed in the decrease in intensity of both absorption and luminescence spectra, where the luminescence band is shifted toward shorter wavelengths and is broadened. The shift of the luminescence band is connected with the decrease in particle size, while the broadening of the luminescence spectrum is connected with increasing spread in the nanoparticle size due to photooxidation [5,6].In [9,10], the effect of the matrix on the photostability of nanocrystals was studied, and it was shown that the photostability is af...

Approximately 102‐fold enhancement of Raman scattering by ultramarine microcrystals is reported by means of interaction with silver nanoparticles in films and powders. Theoretical modeling predicts the maximal 1010‐fold enhancement in close vicinity of a silver spherical nanoparticle (0.24 nm) with rapid decay of enhancement factor to 1 in the range of approximately 50 nm. Experimental enhancement factor is treated as overall effect within the small portion of every microcrystal in the close vicinity of silver nanoparticle(s). The results are considered as an important extension of traditional surface enhanced molecular Raman spectroscopy towards bigger inorganic probes. Copyright © 2012 John Wiley & Sons, Ltd.

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