No abstract

The vibrational spectroscopy of semiconductor nanostructures can provide important information on their structure. In this work, experimental Raman and infrared spectra are compared with vibrational spectra of CdSe/CdS core/shell nanoplatelets calculated from first principles using the density functional theory. The calculations confirm the two-mode behavior of phonon spectra of nanostructures. An analysis of the experimental spectra reveals the absence of modes with a high amplitude of vibrations of surface atoms, which indicates their strong damping. Taking into account the difference in the damping of different modes and their calculated intensities, all bands in the spectra are unambiguously identified. It is found that the frequencies of longitudinal optical modes in heterostructures are close to the frequencies of LO phonons in bulk strained constituents, whereas the frequencies of transverse modes can differ significantly from those of the corresponding TO phonons. It is shown that an anomalous thickness dependence of CdS TO mode is due to a noticeable surface relaxation of the outer Cd layer in the nanostructure.

Colloidal semiconductor nanoparticles have a great potential for designing high-quality white-light-emitting diodes (WLEDs). However, the nanoparticles suffer from the reabsorption effect due to the characteristic small Stokes-shifts, which limits the power conversion efficiency of the light sources. In order to resolve this problem, absorption and emission spectra of the nanoparticles should be separated. Here, we report on gradient alloy CdSe 1−x S x nanoplatelets (NPLs), which allow for suppression of the reabsorption. Thanks to the gradient composition, the S-rich domains of CdSe 1−x S x NPLs behave as an efficient antenna, adsorbing light and funneling the generated carriers into the Se-rich domains, where they recombine. The gradient structure of CdSe 1−x S x NPLs allows one to control the overlap of the emission and absorption spectra simply by varying their composition. By controlling the composition of CdSe 1−x S x NPLs, their photometric parameters, including chromaticity color coordinates, color rendering index (CRI), and correlated color temperature (CCT), can be tuned. Due to the wide trap-assisted emissions associated with unsaturated S/Se surface atoms, CdSe 1−x S x NPLs demonstrate exceptionally high CRI values ranging from 87 up to 94 at CCT values in the range of 2509−6448 K, making them promising for high-quality white-light generation. Finally, WLEDs based on as-obtained gradient alloy CdSe 1−x S x NPLs are fabricated that show high luminous efficiencies (LE) reaching values up to 250 lm/W and CRI values as high as 91, demonstrating their potential for commercial applications.

Tip-enhanced Raman scattering (TERS) has recently emerged as a powerful technique for studying local properties of low dimensional materials. Being a plasmon driven system, a dramatic enhancement of the TERS...

Inverse photonic crystal films were prepared by photopolymerization of ethoxylate trimethylolpropane triacrylate (ETPTA) using opal-type templates. Their high quality was proved by investigations of structural and optical properties. The unexpectedly high refractive index, nETPTA ≈ 1.67, of polymerized ETPTA was obtained from a numerical approximation of the spectral positions of the reflectance peak of the films at different incidence angles. Fabricated samples were tested as sensors for water-ethanol mixtures, and a monotonous increase in the stop band shift with an increase in ethanol concentration was established.