3 research outputs found
Mixing of Excitons in Nanostructures Based on a Perylene Dye with CdTe Quantum Dots
Semiconductor quantum dots of the A2B6 group and organic semiconductors have been widely studied and applied in optoelectronics. This study aims to combine CdTe quantum dots and perylene-based dye molecules into advanced nanostructure system targeting to improve their functional properties. In such systems, new electronic states, a mixture of WannierâMott excitons with charge-transfer excitons, have appeared at the interface of CdTe quantum dots and the perylene dye. The nature of such new states has been analyzed by absorption and photoluminescence spectroscopy with picosecond time resolution. Furthermore, aggregation of perylene dye on the CdTe has been elucidated, and contribution of Förster resonant energy transfer has been observed between aggregated forms of the dye and CdTe quantum dots in the hybrid CdTe-perylene nanostructures. The studied nanostructures have strongly quenched emission of quantum dots enabling potential application of such systems in dissociative sensing
Colloidal Cu-Zn-Sn-Te Nanocrystals: Aqueous Synthesis and Raman Spectroscopy Study
Cu-Zn-Sn-Te (CZTTe) is an inexpensive quaternary semiconductor that has not been investigated so far, unlike its intensively studied CZTS and CZTSe counterparts, although it may potentially have desirable properties for solar energy conversion, thermoelectric, and other applications. Here, we report on the synthesis of CZTTe nanocrystals (NCs) via an original low-cost, low-temperature colloidal synthesis in water, using a small-molecule stabilizer, thioglycolic acid. The absorption edge at about 0.8â0.9 eV agrees well with the value expected for Cu2ZnSnTe4, thus suggesting CZTTe to be an affordable alternative for IR photodetectors and solar cells. As the main method of structural characterization multi-wavelength resonant Raman spectroscopy was used complemented by TEM, XRD, XPS as well as UV-vis and IR absorption spectroscopy. The experimental study is supported by first principles density functional calculations of the electronic structure and phonon spectra. Even though the composition of NCs exhibits a noticeable deviation from the Cu2ZnSnTe4 stoichiometry, a common feature of multinary NCs synthesized in water, the Raman spectra reveal very small widths of the main phonon peak and also multi-phonon scattering processes up to the fourth order. These factors imply a very good crystallinity of the NCs, which is further confirmed by high-resolution TEM
Self-Organized SERS Substrates with Efficient Analyte Enrichment in the Hot Spots
One of the requirements of an efficient surface-enhanced
Raman
spectroscopy (SERS) substrate is a developed surface morphology with
a high density of âhot spotsâ, nm-scale spacings between
plasmonic nanoparticles. Of particular interest are plasmonic architectures
that could enable self-localization (enrichment) of the analyte in
the hot spots. We report a straightforward method of fabrication of
efficient SERS substrates that comply with these requirements. The
basis of the substrate is a large-area film of tightly packed SiO2 spheres formed by their quick self-assembling upon drop casting
from the solution. Thermally evaporated thin Ag layer is converted
by quick thermal annealing into nanoparticles (NPs) self-assembled
in the trenches between the silica spheres, i.e., in the places where
the analyte molecules get localized upon deposition from solution
and drying. Therefore, the obtained substrate morphology enables an
efficient enrichment of the analyte in the hot spots formed by the
densely arranged plasmonic NPs. The high efficiency of the developed
SERS substrates is demonstrated by the detection of Rhodamine 6G down
to 10â13 mol/L with an enhancement factor of âŒ108, as well as the detection of low concentrations of various
nonresonant analytes, both small dye molecules and large biomolecules.
The developed approach to SERS substrates is very straightforward
for implementation and can be further extended to using gold or other
plasmonic NPs