By using optical spectroscopic methods the effects of spatial confinement and surface in phonon and electron excitations in colloidal II-VI nanocrystals (NCs) have been investigated. Dependence of the frequency of optical phonons and their line shape in the Raman scattering spectra, as well as the magnitude of the electron-phonon coupling (EPC) on the NC size range of 2-5 nm was established experimentally. For NC size below 2 nm, their phonon spectrum undergoes qualitative changes indicative of structural rearrangement and confirms the theoretical predictions regarding the structural relaxation in ultrasmall NC, in which the predominance of surface atoms over "bulk" ones takes place. It is shown that the use of different ligands to stabilize the NCs and the conditions for excitation of the Raman spectra affects the resulting phonon spectra, thus explaining a significant spread of experimental data in the literature before. For the first time, the features in the Raman spectrum of NCs, located above the maximum frequency of optical phonons of the corresponding bulk crystal, is described. This spectral feature get enhanced with decreasing NC size and is explained by the manifestation of the density of phonon states associated with surface bonds. For core/shell NCs CdSe/CdS and CdSe/ZnS, the fact of interfu-sion at the heterointerface, extending over about 3-4 monolayers, has been established. The evolution of mechanical stresses in a core/shell NCs was systematically studied as a function of the thickness of the shell. It has been established that the deposition of the shell also causes significant changes in the phonon spectrum of the core. In particular, a narrowing of the LO-phonon peak of the core is attributed to improved structural homogeneity on the core surface when the interface interface with the shell is formed. The detected decrease in the 2LO/LO intensity ratio indicates a weakening of the EPC for the core phonons, which is explained by a significant decrease in their overlap with the exciton partially tunneling into the shell. For the first time, the phonon spectra of two-dimensional "core/shell" NCs, nanoplate-lets, have been investigated. Their qualitative differences from spectra of spherical core/shell NCs are revealed. The experimental data obtained show, in particular, that the vibrational optical modes of two-dimensional NCs are of mixed-type character, which was predicted theoretically for spherical NCs, but their experimental confirmation was hindered by size dispersion of spherical NCs. The methodology of structural research on the basis of the analysis of phonon spectra developed for II-VI NCs was applied the first time for establishing the phonon spectrum of "core-shell" systems based on more complex, but extremely relevant from the point of view of applications, systems such as CuInS(e)2/ZnS and Zn-Cu-In-S/ZnS. The resonant character of their phonon Raman spectra is established, despite the featureless opti-cal spectra.
Key words: semiconductor nanocrystals, phonons, combined light scattering, nucleus-shell structure, photoluminescence, optical absorption.
