The II-VI semiconductor nanocrystals, obtained by various techniques, attract continuous interest due to confinement-related effects in their optical properties, leading to broad applications. Binary and ternary II-VI nanocrystals have been extensively studied by phonon spectroscopy with an emphasize on nanometer-size-related effects (phonon confinement, marked contribution of surface phonons due to the high surface-to-volume ratio, size dispersion of nanocrystals within the ensemble). For ternary II-VI nanocrystals, phonon spectroscopy has been proven to be a reliable and non-destructive tool for determinaton of nanocrystal composition for both one-mode and two-mode systems. As regards quaternary II-VI nanocrystals, their studies are extremely scarce.

Here we report on the studies of the quaternary Cd_1-yZn_yS_1-xSe_x and CdS_1-x-ySe_xTe_y nanocrystals phonon spectra obtained in a borosilicate glass by diffusion-limited growth. The nanocrystal composition was varied by the concentration of their components in the initial mixture as well as by the variation of the heat treatment conditions (temperature and duration). Resonant Raman scattering studies were performed using a Dilor XY 800 triple monochromator with a CCD camera with excitation by Ar⁺ and Kr⁺ ion laser light being tuned from 476.5 to 647.1 nm. Measurements were performed at room temperature.

The Cd_1-yZn_yS_1-xSe_x nanocrystals, formed in the glass matrix, were observed to possess a basically two-mode type of the phonon spectrum transformation (for sulphur-rich nanocrystals) and a more complicated transformation type (for the nanocrystals with higher Se content). For CdS_1-x-ySe_xTe_y nanocrystals a three-mode type of the phonon spectrum transformation was clearly revealed. The obtained results are compared with the calculations and experimental data for the bulk crystals of similar systems. The  application possibilities of the phonon spectra to estimate the quaternary nanocrystal composition  are discussed.

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