V. N. Bogomolov

Spontaneous emission of dye molecules, semiconductor nanocrystals, and rare-earth ions in opal-based photonic crystals

Photonic crystals based on silica colloidal crystals (artificial opals) exhibit pronounced stopbands for electromagnetic wave propagation and the corresponding modification of the photon density of states in the visible range. These spectrally selective features can be enhanced by impregnating opals with higher refractive materials like, e.g., polymers. Doping of these structures with dye molecules, semiconductor nanoparticles (quantum dots), and rare-earth ions provides a possibility to examine the challenging theoretical predictions of the inhibited spontaneous emission in photonic bandgap (PBG) materials. First experiments are discussed in which pronounced modification of spontaneous emission spectra and noticeable changes in decay kinetics were observed.

Electrons and photons in mesoscopic structures: quantum dots in a photonic crystal

The synthesis and properties of a photonic crystal doped with quantum dots are reported. The structure exhibits a two-stage self-organization of silica nanoparticles along with quantum confinement effects in semiconductor colloids. The interplay of electron and photon confinement results in controllable spontaneous emission from the mesoscopic structure.

Spontaneous emission of organic molecules and semiconductor nanocrystals in a photonic crystal

Photonic crystals based on artificial colloidal silica crystals (opals) exhibit pronounced stop bands for electromagnetic wave propagation and the corresponding modification of the photon density of states in the visible range. Doping of these structures with dye molecules and semiconductor nanoparticles (quantum dots) provides a possibility to examine the predictions of the inhibited spontaneous emission in photonic band-gap materials. First experiments are reviewed in which pronounced modification of spontaneous emission spectra and noticeable changes in decay kinetics were observed.

Effect of a photonic band gap in the optical range on solid-state SiO2 cluster lattices — opals

It is shown that synthetic opals — cubic face-centered lattices of SiO2 clusters — are systems which exhibit a number of properties of photonic crystals in the visible-light range. By filling the voids (pores) in such lattices with different materials it is possible to vary the optical contrast of the medium and to obtain crystals of both the lattice of spheres type and its three-dimensional replica. It is shown that under conditions of identical optical contrast and in the presence of an additional optical inhomogeneity of the spheres, the transparency of the lattice of spheres is lower than that of its replica based on homogeneous media. A refractive index modulation of 1.266 was achieved in the lattice of spheres.

Fabrication of regular three-dimensional lattices of submicron silicon clusters in an SiO2 opal matrix

Silicon is now the most important material in modern solid-state electronics. Regular systems of silicon nanoclusters containing up to 1014 cm−3 elements were obtained in a sublattice of opal (SiO2) voids. By using three-dimensional dielectric matrix-carriers similar to opal, it may be possible to obtain three-dimensional ensembles of semiconductor nanodevices. Various parameters of these “opal-silicon” nanocomposites were measured.

Photonic band gap effect in a solid state cluster lattice

Abstract We report on the photonic band gap phenomenon in the visible range in a three-dimensional dielectric lattice formed by close-packed spherical silica clusters. The spectral position and the spectral width of the optical stop band depend on the direction of light propagation with respect to the crystal axes of the lattice and on the relative cluster-to-cavity refraction index. Manifestations of the photonic pseudogap have been established for the transmission spectra and for the emission spectra of the dye molecules embedded in the intercluster cavities. Slowing down of the luminescence decay has been observed which is attributed to the influence of the photon density of states on the spontaneous emission rate.

Thermal conductivity of a new type of regular-structure nanocomposites: PbSe in opal pores

Samples of an opal-based nanocomposite with PbSe embedded chemically into opal voids have been produced. Their thermal conductivity (in the 16–100-K range), the Seebeck coefficient (16–100 K), and electrical resistivity (5–100 K) have been measured. The thermal conductivity data permit a conclusion that a new type of substance has been produced, namely, nanocomposites having a regular structure, with each nanocomponent being a microcrystal. A concept of quasi-chemical bonding forming in nanocomponent lattices is introduced.

Phonon propagation through photonic crystals—media with spatially modulated acoustic properties

The thermal conductivity κ of photonic crystals differing in degree of optical homogeneity (single crystals of synthetic opals) was measured in the 4.2–300 K temperature range. The thermal conductivity revealed, in addition to the conventional decrease in comparison with solid amorphous SiO2 characteristic of porous solids, a noticeable decrease for T<20 K, the range wherein the phonon wavelength in amorphous SiO2 approaches the diameters of the contact areas between the opal spheres. This effect is enhanced in the case of phonon propagation along the SiO2 sphere chains (six directions in the cubic opal lattice). The propagation of light waves (photons) through a medium with spatially modulated optical properties (photonic crystals) is presently well studied. The propagation of acoustic waves through a medium with spatially modulated acoustic properties (phononic crystals) may also reveal specific effects, which are discussed in this paper; among them are, e.g., the ballistic mode of phonon propagation and waveguide effects.

Silicon nanocluster formation under electron-beam-induced modification of a silicate matrix

A cathodoluminescence band in the green spectral region is observed in silicate matrices when the excitation density exceeds a certain threshold value. This band is due to the formation of silicon nanoclusters 4–5 nm in size and becomes manifest at SiO2/Si interfaces when impurities are introduced into the silicate matrix, as well as under electron-beam irradiation.

Superconductivity as Bose-Einstein Condensation in High- and Low-Temperature Superconductors (Diluted Metals)

The structures and parameters of some low-and high-temperature superconductors (HTSCs) are considered, adopting a O2− ion radius of 0.5–0.6 Å. The transitions in ultrahigh-Tc unstable compositions Yba2Cu3Se7 (at Tc = 371 K) and Ag2(Ag3Pb2H2O6) (Tc ∼ 400 K) and in low-Tc composition SrNbxTi1−xO3 (Tc ∼ 0.3 K) to the superconducting state correspond to the Bose-Einstein condensation. The structural instability of the first HTSC is related to the fact that the ion radius of Se2− (∼1 Å) is significantly greater than that of O2−; the properties of the second HTSC are quasi-one-dimensional and impractical. The electron densities and effective masses in some stoichiometric and nonstoichiometric (nanocomposite) HTSCs are evaluated. Large effective masses of electrons in HTSCs can be indicative of the existence of polarons (bipolarons) in such systems. New potential HTSC compositions (MgxWO3) are mentioned.