Synthesis and Characterization of Organically Soluble Cu-Doped ZnS Nanocrystals with Br Co-activator

2011: J. Phys. Chem. C

Carley Corrado, Jason K. Cooper, Morgan Hawker, Jenny Hensel, Grant Livingston, Sheraz Gul, Brian Vollbrecht, Frank Bridges, Jin Z. Zhang

Fluorescent, organically soluble Cu and Br codoped ZnS nanocrystals (NCs) were synthesized and characterized for the potential application of AC electroluminescent (EL) lighting devices. The doped NCs were optically characterized using UV–vis, photoluminescence (PL), Fourier transform infrared (FTIR), and time-resolved PL spectroscopy, and structurally characterized using transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS). The PL emission of the undoped ZnS NCs upon λex = 280 nm was broad with a peak in the range of 450–470 nm, depending on the preparation of the NCs. Upon doping ZnS NCs with Cu, the PL emission was increased slightly with little change in spectral features. When Br dopant was added in addition to Cu, the codoped ZnS NCs showed much stronger PL emission (∼5 × ) compared to the undoped or Cu-doped sample. In conjunction with time-resolved PL results, this enhanced emission is attributed to a donor–acceptor (D–A) type of transition, between the Br electron trap and Cu hole trap, respectively. The time-resolved PL studies provide important information about the lifetimes of associated states and help to gain new insights into the nature of the states involved in the observed PL. The EXAFS data reveal that Br is clearly incorporated into the NCs. Increased disorder around Br with increasing Cu suggests that the Br is located near Cu within the ZnS lattice. This study demonstrates successful Cu-doping of ZnS NCs by using a halogen coactivator, for the first time, in an organic solvent. Organic soluble systems have proven more advantageous for preparation of high-quality thin films.

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