Resonant Raman studies of compositional and size dispersion of CdS_1−xSe_xnanocrystals in a glass matrix

Abstract

Resonant Raman scattering spectra of glass-embedded CdS 1−x Se x nanocrystals are measured and complemented with TEM and optical absorption as well as photoluminescence data. The selectivity of the resonant Raman process not only for the size, but also for the composition of nanocrystals within the ensemble, is directly observed in the dependence of phonon band frequency, linewidth and shape on the excitation wavelength.

Phonon spectra of quaternary Cd1–yZny S1–xSex semiconductor nanocrystals grown in a glass matrix

“…In all cases the spectra exhibit a typical two-mode behaviour with distinct longitudinal optical selenide-like LO 1 and sulphide-like LO 2 phonon peaks. For the samples, obtained at the least intense heat treatment, the LO phonon frequencies agree well with the values obtained earlier for the glass-embedded CdS 1-x Se x NCs [3,4,[6][7][8][9]. With the increase of the heat treatment temperature and duration the observed LO phonon frequencies increase as well as those of the two-phonon bands.…”

“…It is especially well elaborated for CdS 1-x Se x with a two-mode compositional behaviour. In II-VI NCs only LO phonon maxima are observed, converging with x, and the composition can be determined from the LO phonon peak position difference [3,[6][7][8][9]. ZnS 1-x Se x solid solutions are also characterized by two-mode behaviour [16].…”

Phonon spectroscopy of CdSe1–xTex nanocrystals grown in a borosilicate glass

“…Some estimations of the compositional dispersion can be made from the Raman spectra. Since resonant Raman scattering is sensitive both to the nanocrystal size and composition which determine the electronic spectrum of the system, by probing the sample with different Raman excitation wavelength, one can change the conditions of incoming or outgoing Raman resonance and excite a subsystem of nanocrystals corresponding to a much narrower range of sizes and/or compositions than the one present in the sample [9]. In our case this is illustrated by Fig.…”

Surface phonons in CdS1–xSex nanoparticles embedded in a dielectric medium

“…This fast and non-destructive technique has proved its efficiency in the determination of the average NC composition from the CdS-like and CdSe-like LO phonon frequencies [5][6][7][8][9][10] as well as in the estimation of the NC size from the Raman scattering by acoustic phonons [11][12][13]. However, these objects have been also very convenient to study fundamental effects, specific for the phonon spectra of nanometric systems -nonzero-wavevector phonon contribution due to phonon confinement [7][8][9][14][15][16], compressive strain due to the glass matrix pressure [17,18], compositional and size dispersion of NCs within the ensemble [10] and scattering by surface phonons due to marked surface-to-volume ratio [6,7,9,19,20]. The surface phonon characteristics have been reported only for a limited set of x values, and the obtained experimental data are insufficient to discuss their consistency with theoretical predictions.…”

“…Second-order Raman spectra contain 2LO 1 (near 400 cm -1 ), LO 1 +LO 2 (around 480-490 cm -1 ), and 2LO 2 (near 600 cm -1 ) phonon bands, whose frequencies and intensities are also composition-dependent. The difference of the CdS-like LO 2 and CdSe-like LO 1 phonon peak frequencies is a good and reliable measure of the NC composition [5,9,10] from the Raman spectra.…”