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Based on X-ray diffraction analysis, Auger spectroscopy, and Raman scattering, it is shown that carbonization of porous silicon at temperatures of 1200–1300°C results in formation of silicon carbide nanocrystals 5–7 nm in size. The growth of 3C-SiC nanocrystals of fixed size d proceeds as follows. Silicon nanocrystals with d = 3–7 nm pass into the liquid phase, thereby effectively participating in the growth of silicon carbide. After the size of a crystallite has achieved a critical value determined by the equality of its melting point and environmental temperature, the crystallite solidifies and virtually ceases to grow. As a result, a nanocrystalline Si-SiC-amorphous SiC heterostructure is obtained. [ABSTRACT FROM AUTHOR]

The Raman and photoluminescence (PL) spectra of nanocrystalline zinc oxide produced by mechanochemical synthesis were measured using a pulsed nitrogen laser (337.1 nm) and xenon lamp (360 nm) as excitation sources in PL measurements and a cw Nd:YAG laser in Raman measurements. PL was observed in the range 400–800 nm. The Raman spectrum of nanocrystalline (90 nm) ZnO was compared to that of coarsegrained ZnO. The Raman bands of nanocrystalline zinc oxide were found to be shifted to lower frequencies and broadened. Laser radiation was shown to cause local heating of zinc oxide up to 1000 K, resulting in photoinduced formation of zinc nanoclusters. Mixtures of zinc oxide and sodium chloride powders are heated to substantially lower temperatures. Under nitrogen laser excitation, the green PL band (535 nm), characteristic of bulk ZnO, is shifted to longer wavelengths by 85 nm. The results are interpreted in terms of light confinement in zinc oxide microclusters consisting of large number of nanocrystallites. The photoinduced processes in question may be a viable approach to producing metal-insulator structures in globular photonic crystals, opals, filled with zinc oxide. [ABSTRACT FROM AUTHOR]

The results of investigations of the structure and optical properties of films of fullerene C[sub 60] are reported. The films were obtained by vacuum thermal evaporation on substrates from heat-resistant polymers (polyacrylonitrile and cyclized polyacrylonitrile in composition with polyimide). The structure of C[sub 60] films was determined by X-ray diffractometry. In all diffraction patterns of fullerene films, their structure manifests itself through reflections from the (111), (220), and (311) planes. Cubic C[sub 60] films were obtained by fullerene deposition at substrate temperatures as high as 200°C. Atomic force microscopy of the film surface revealed the existence of a laminated structure. The infrared (IR) transmission spectra are indicative of the presence and constancy of the position of characteristic bands of C[sub 60] (527, 576, 1183, and 1428 cm[sup -1]) for all fullerene films. The investigation of photoluminescence of fullerene films revealed bands whose energy position both exceeded typical values for molecular C[sub 60] or fell below these values. This circumstance is caused by the interaction between the electron π systems of C[sub 60] and the polymer substrate at the heterointerface, as well as by the photopolymerization reaction of fullerene under the effect of high-energy laser radiation and by the emergence of trap centers in the films. [ABSTRACT FROM AUTHOR]

Based on the investigation of the spectra of two-photon excited luminescence of powder zinc sulfide electroluminophors, their electroluminescence spectra measured under different conditions at different stages of degradation, and also the data known from the literature dealing with the study of the microstructure of ZnS:Cu crystals, a conclusion has been drawn that the centers of green and blue luminescence are nonuniformly distributed over the luminophor grains. It is presumed that close by the surface of the grains, near the “second phase–zinc–sulfide” interface (the regions of energy barriers responsible for impact multiplication of charge carriers in prebreakdown electroluminescence) the centers of green luminescence predominate, while the blue luminescence centers are located at the periphery of the barriers, in deeper regions of the crystals. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) and photoexcitation spectra of carbonized porous silicon (por-Si) doped with gallium in the course of a high-temperature annealing were studied. It is shown that carbonization leads to the formation of a heterojunction between 3C-SiC nanograins and silicon quantum wires. The spectrum of PL from gallium-doped silicon carbide nanograins is shifted by 0.35 eV toward higher energies relative to the spectrum of bulk por-Si and exhibits several features related to the radiative annihilation processes involving phonons and donor-acceptor (N-Ga) pairs. The PL excitation spectra of carbonized por-Si display two resonance bands with the energies E[sub 1] = 2.8-3.1 eV and E[sub 2] = 3.2-3.7 eV. [ABSTRACT FROM AUTHOR]

The time dependence of the decay of the photoluminescence of porous silicon subjected to high temperature carbonization (1000-1200°C) and simultaneously doped with B, P, Ga, or A1 atoms is investigated. The boron-doped samples show an anomalously long decay time for the blue-green (2.4 eV) photoluminescence band. In addition, in this case oscillations with a period of 50 ms are observed in the photoluminescence decay curve. [ABSTRACT FROM AUTHOR]

A promising new method of modifying the spectral characteristics of porous silicon and stabilizing its photoluminescence is proposed using high-temperature carbonization. Investigations have shown that carbonized samples exhibit stable photoluminescence and the spectral peak is shifted into the rf-blue range. [ABSTRACT FROM AUTHOR]