B. S. Razbirin

Fractals of graphene quantum dots in photoluminescence of shungite

Viewing shungite as loosely packed fractal nets of graphene-based (reduced graphene oxide, rGO) quantum dots (GQDs), we consider photoluminescence of the latter as a convincing proof of the structural concept as well as of the GQD attribution to individual rGO fragments. We study emission from shungite GQDs for colloidal dispersions in water, carbon tetrachloride, and toluene at both room and low temperatures. As expected, the photoluminescence of the GQD aqueous dispersions is quite similar to that of synthetic GQDs of the rGO origin. The morphological study of shungite dispersions shows a steady trend of GQDs to form fractals and to drastically change the colloid fractal structure caused by the solvent exchange. Spectral study reveals a dual character of the emitting centers: individual GQDs are responsible for the spectra position while the fractal structure of GQD colloids ensures high broadening of the spectra due to structural inhomogeneity, thus causing a peculiar dependence of the photoluminescence spectra on the excitation wavelength. For the first time, photoluminescence spectra of individual GQDs were observed in frozen toluene dispersions, which paves the way for a theoretical treatment of the GQD photonics.

Fullerene-cluster amplifiers and nanophotonics of fullerene solutions

New enhanced linear optical effects were found for crystalline solutions of fullerenes in toluene. They are referred to as enhanced Raman scattering and enhanced luminescence of both solvent and fullerenes and are attributed to clustering the solute molecules themselves and solute and solvent molecules together. The effects are due to the excitation of localized charge-transfer excitons of the fullerene nanoclusters which makes the latter act as amplifiers of local electric fields.

A study of thick 3C-SiC epitaxial layers grown on 6H-SiC substrates by sublimation epitaxy in vacuum

Abstract3C-SiC epitaxial layers with a thickness of up to 100 µm were grown on 6H-SiC hexagonal substrates by sublimation epitaxy in vacuum. The n-type epitaxial layers with the area in the range 0.3–0.5 cm2 and uncompensated donor concentration Nd − Na ∼ (1017–1018) cm−3 were produced at maximum growth rates of up to 200 µm/h. An X-ray analysis demonstrated that the epitaxial layers are composed of the 3C-SiC polytype, without inclusions of other polytypes. The photoluminescence (PL) spectrum of the layers was found to be dominated by the donor-acceptor (Al-N) recombination band peaked at hv ≈ 2.12 eV. The PL spectrum measured at 6 K was analyzed in detail. It is concluded that the epitaxial layers obtained can serve as substrates for 3C-SiC-based electronic devices.

Enhanced Raman scattering provided by fullerene nanoclusters

Two new nonlinear optic effects are observed in crystalline solutions of fullerenes in toluene and carbon tetrachloride. Both are provided by a self-clustering of the solute molecules and are referred to fullerene-enhanced Raman scattering and solvent-enhanced luminescence. The effects are induced by the excitation of charge-transfer states of the fullerene nanoclusters, which makes the latter act as amplifiers of local electric fields.

Absorption line spectrum of the C60Cl24 halofullerene

AbstractOptical spectra of the C60Cl24 halofullerene in the crystalline state, as well as of C60Cl24 matrixisolated molecules, were studied. In both cases, a rich line structure was revealed in absorption spectra in the energy region 1.5–3.0 eV. An energy diagram of the electronic levels of the molecule which are responsible for the observed optical transitions is proposed. The parameters of the geometrical structure of the C60Cl24 molecule were calculated under the assumption of its having Th symmetry. These data were used in a theoretical study of the embedment of the C60Cl24 molecule in a toluene crystal matrix, which leads to the formation of a fine spectral structure (an analog of the Shpol’ski

Electronic and photophysical properties of C60Cl24

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The nature of enhanced linear and nonlinear optical effects in fullerene solutions

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Shpolski effect in optical spectra of frozen solutions of the organic C60 fullerene derivative in toluene

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