The formation of silica nano- and microparticles has been studied during growth by the modified Stöber-Fink-Bohn (SFB) method. It has been experimentally found that the density and fractal structure of particles vary with size as they grow from 70 to 2200 nm. We propose a model of particle structure which is a dense primary particle core and is composed of concentric secondary particle shells terminating in dense primary particle layers.

Multiphonon resonant Raman scattering (RRS) was studied in unintentionally doped bulk $\mathrm{ZnO}$ crystals and layers, including nanostructured and highly conductive films, excited by 351.1 and $363.8\mathrm{nm}$ laser lines in the temperature interval from 10 to $300\mathrm{K}$. The variation of resonant conditions with sample temperature and wavelength of the excitation laser line allowed us to discriminate between the incoming and outgoing exciton mediated RRS by LO phonons. The quenching of luminescence and enhancement of Raman scattering in nanostructured $\mathrm{ZnO}$ layers grown on single-layer opals enabled us to observe the Raman signal in resonant configuration thus making possible to study multiphonon RRS by Fröhlich-type vibrational modes related to nanocrystallites with sizes less than $50\mathrm{nm}$. The emission spectra of highly conductive $\mathrm{ZnO}$ films grown on porous $\mathrm{InP}$ substrates were found to consist of multiphonon RRS lines superimposed on a broad asymmetric near band gap photoluminescence (PL) band. The occurrence of PL and RRS in highly conductive layers is attributed to tailing of the density of states caused by potential fluctuations and to the breakdown of the wave-vector conservation due to randomly distributed impurities (intrinsic defects).

The photoluminescence (PL) of ZnO-opal structures excited by a 351.1 nm laser line was studied. The fabrication of these structures was done by infiltration of ZnO from an aqueous solution of zinc nitrate into opal matrices. It was observed that the emission spectrum of thick ZnO layers grown on the surface of bulk opals exhibited narrow PL bands associated with the recombination of bound and free-excitons. The results showed that the strong exciton-LO phonon and exciton-Frohlich mode coupling in ZnO nanostructures was deduced from the analysis of multiphonon excitonic resonant Raman scattering.This work was supported by INTAS under Grant No. 01-0796. ISSP authors are grateful for the financial support received from the Russian Foundation for Basic Research (Project No. 01-02-97024) and from the Russian Federation Government under Contract No. 40.012.1.1.11.54.Peer Reviewe

The conditions of synthesis of silicon dioxide particles with a high degree of monodispersity have been investigated. The particles have been synthesized using both the hydrolysis of tetraethoxysilane

The intrinsic structure of spherical SiO₂ particles synthesized by hydrolysis of tetraethyl orthosilicate in an alcohol-water-ammonia medium was studied using transmission electron microscopy. It was established that the relatively large spherical silica particles were “tertiary” structures made up of smaller spherical particles (“ secondary” particles), which in turn consisted of even smaller primary spherical particles 5–10 nm in diameter. It was shown that, under the experimental conditions, the large SiO₂ particles can contain a central core comprising primary particles surrounded by several layers of secondary particles smaller than the core diameter.