ABSTRACT
Stable colloidal solutions of zinc oxide in dimethylsulfoxide were synthesized via interaction between zinc(II) acetate and tetraalkylammonium hydroxides (alkyl-ethyl, propyl, butyl, and pentyl). Colloids of ZnO emit photoluminescence in a broad band with a maximum at 2.3-2.4 eV with quantum yields of up to 9-10% at room temperature and 15-16% at 80 K. The photoluminescence is supposed to originate from the radiative recombination of conduction band electrons with holes captured by deep traps having corresponding states in the band gap 1.0-1.2 eV above the valence band edge. The size of colloidal ZnO nanocrystals depends on the duration and temperature of the post-synthesis treatment and varies in the range of 3-6 nm. Growth of the ZnO nanocrystals can be terminated at any moment of the thermal treatment by freezing the colloidal solution or by addition of tetraethyl orthosilicate which hydrolyses forming core-shell ZnO@SiO2 particles. ZnO nanocrystals introduced into polyethyleneimine films can be used as an active component of an LED emitting at an applied voltage higher than 13 V.
Subject(s)
Colloids/chemistry , Dimethyl Sulfoxide/chemistry , Zinc Oxide/chemistry , Biomarkers/chemistry , Cations , Hydrolysis , Light , Luminescence , Nanoparticles/chemistry , Nanotechnology , Photochemical Processes , Polyethyleneimine/chemistry , Scattering, Radiation , Silanes/chemistry , Surface Properties , TemperatureABSTRACT
The effect of shells of various thicknesses on the vibrational resonant Raman spectra of CdSe/ZnS core-shell nanoparticles is studied. The dependence of the core-shell structure on the method of shell deposition is derived from a comparison of the vibrational and photoluminescence spectra of nanoparticles. Along with the appearance of peaks attributed to the shell, the phonon spectrum of the core undergoes significant changes upon shell growth. The change of the CdSe LO peak lineshape in core-shell nanoparticles is discussed with respect to possible changes in the spectrum of both optical and acoustical phonons upon shell formation. Based on the observed decrease of the CdSe 2LO/LO peak intensity ratio, a weakening of exciton coupling to the CdSe LO phonon upon ZnS shell deposition is supposed. The change in the carrier localization volumes upon shell formation is discussed as a possible reason for the reduced coupling.
