Annealing of ZnS nanocrystals grown by colloidal synthesis

Abstract

ZnS nanocrystals (NCs) capped with tetramethylammonium (TMAH) were synthesized from ZnCl2·2H2O and thiourea using a wet chemical process. Further treatments of the nanocrystals such as aging, and annealing have been conducted to examine the stability of the grown samples. The X-ray diffraction spectra show that the crystal has a zinc blende structure with particle size of about 2nm. The evidence of nanocrystalline character is also clear in the UV–Vis absorption that shows an excitonic peak at about 236nm (5.2eV) arising from band edge transitions. A photoluminescence emission peak centered at about 450nm (2.7eV) is attributed to transitions between shallow donors and Zn+ vacancies. Both absorption and photoluminescence spectra show that sample aging does not affect the characteristics of the sample, possibly due to protection by TMAH capping. Annealing at 700°C and 900°C results in the red shift of the photoluminescence.