Confinement effects on optical phonons in spherical, rod-, and tetrapod-shaped nanocrystals detected by Raman spectroscopy

Spherical, rod- and tetrapod shaped CdSe nanocrystals are investigated by Raman spectroscopy and the longitudinal-optical and surface optical phonons are observed. We find that the position of the longitudinal-optical phonon slightly red-shifts with decreasing diameter, whereas the position of the surface optical phonon depends significantly on diameter and length of the rods or the tetrapod arms

Confined Optical Phonon Modes in Aligned Nanorod Arrays Detected by Resonant Inelastic Light Scattering

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Near-UV optical-cavities n Ga_2O_3 nanowires

In this Letter, we report optical confinement in the near-ultraviolet (near-UV) range in Ga2O3 nanowires (NWs) by distributed Bragg reflector (DBR) nanopatterned cavities. High-contrast DBRs, which act as the end mirrors of the cavities of the desired length, are designed and fabricated by focused ion beam etching. The resonant modes of the cavities are analyzed by micro-photoluminescence measurements, analytical models, and simulations, which show very good agreement between each other. Experimental reflectivities up to 50% are obtained over the 350-410 nm region for the resonances in this wavelength range. Therefore, Ga2O3 NW optical cavities are shown as good candidates for single-material-based near-UV light emitters

Shape Dependence of the Scattering Processes of Optical Phonons in Colloidal Nanocrystals Detected by Raman Spectroscopy

We investigated by Raman spectroscopy optical phonon excitations in colloidal CdTe nanocrystals of different shapes. The phonon spectra at excitation energies slightly below the absorption onset showed a strong dependence on the nanocrystal shape. For spherical nanocrystals, we detected broad longitudinal-optical phonon-scattering peaks that were blue shifted from the longitudinal-optical phonon bulk energy by the exciton resonant Stokes shift. These are reminiscent of the phonon replicas reported in fluorescence line-narrowing experiments. Tetrapod-shaped nanocrystals, on the other hand, showed a sharp LO phonon peak that was only slightly blue shifted by confinement effects on the phonon excitations. We propose that the localization of the carriers in the optical excitations is responsible for the different phonon spectra in tetrapods

Direct observation of confined acoustic phonons in the photoluminescence spectra of a single CdSe-CdS-ZnS core-shell-shell nanocrystal

We report on the direct observation of confined acoustic phonons in the photoluminescence spectra of single CdSe-CdS-ZnS nanocrystals, whose ligands were exchanged to poly(ethylene oxide) (PEO) before they were embedded in a PEO matrix. Modeling a nanocrystal as an elastic sphere, the confined acoustic modes can be assigned to purely radial vibrations: the breathing mode and its two first radial harmonics. In addition to acoustic modes, we also observe longitudinal optical modes of the core material and, remarkably, also of both shell materials