Colloidal ZnO nanocrystals in dimethylsulfoxide: a new synthesis, optical, photo- and electroluminescent properties

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.