ИСТИНА

Size/shape-dependent properties of semiconductor nanoparticles coupled with their excellent solution processability are being actively explored for applications in light emitting diodes, solar cells, biomedical labeling, etc. Precise shape control can be achieved by selective ligand attachment, and procedures to grow colloidal nanoparticles with various shapes such as nanorods and tetrapods have been developed. Recently the syntheses of free- standing atomically thin cadmium TEM pictures (a, b) and absorption spectra (c, d) of the CdTe and CdTe/CdS nanoplates respectively. chalcogenide nanoplates with their lateral sizes from tens to hundreds of nanometers, and with defined thicknesses quantified by one monolayer of cadmium chalcogenide were reported. In present work quasi-two-dimensional CdSe and CdTe nanoparticles passivated with oleic acid ligands were prepared by colloidal method. Syntheses were performed at 180-250°C in octadecene under constant argon flow. The platelet formation is induced by the presence of Different populations of CdSe and CdTe colloidal nanoplates with thicknesses of 1-2 nm and lateral sizes of hundreds nm were synthesized. Nanoplate thickness depends on the seed size, and doesn't change during the plate growth. High uniformity of nanoplate thickness within one population causes the appearance of narrow peaks in absorption and luminescence spectra with positions fixed for each population. The absorption spectra of both CdSe and CdTe nanoplates show two well-resolved bands that correspond to the electron-heavy hole and electron-light hole transitions. There is no Stokes shift observed between the low-energy absorption line and the emission line for all nanoplate populations, and each emission line has full width at half-maximum (fwhm) < 14 nm in case of CdSe, and < 8 nm for CdTe, that is in a good agreement with Heterojunction formation allows to tune the spatial confinement of charge carriers, and thus optical properties of semiconductor nanoparticles using band edge engineering. To the best of our knowledge, the synthetic approaches produsing quasi-two-dimensional heteronanostructures were not well documented yet. In present research we investigated CdSe/CdS and CdTe/CdS heteronanostructures obtained by nanoplate ligand exchange resulted in the formation of sulfide monolayer on the nanoplate surface. Ligand exchange was performed via exposure of CdSe and CdTe nanoplates in excess of hexadecanethiol, the process was controlled spectroscopically. In both cases the conservation of nanoplate shape after the sulfide monolayer formation was shown. In case of type I CdSe/CdS heterostructure formation we experimentally observed the red shift of absorption bands (up to 38 nm for the thinnest nanoplate population) with their significant broadening (up to two times for all samples). After the heterostructure formation, the nanoplates are still luminescent, but their quantum yield dropped from 30% for initial CdSe nanoplates to 10- 15% for heterostructures. Formation of sulfide monolayer on the surface of CdTe nanoplates caused rolling of initially flat nanoparticles into nanoscrolls. Monitoring of absorption spectrum evolution during the formation of type II CdTe/CdS heterostructure has shown the decrease of excitonic band without significant spectral shift and the appearance of new low-energy band, which can be attributed to charge-transfer state of spatially separated electron and hole, intensity of this band increases during sulfide layer formation. This work was supported by the Russian Foundation for Basic Research (Grant 13-03-00760).