Growth and photoluminescence properties of PbS nanocubes

Abstract

This paper reports the synthesis of semiconductor nanocrystals of PbSthrough a facile and inexpensive synthetic route between lead acetate[Pb(Ac)2·3H2O] anddithioglycol (HSCH2CH2SH) without any surfactant. The products were characterized by x-ray diffraction (XRD),transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Ramanspectroscopy, x-ray photelectron spectroscopy (XPS) and infrared (IR) spectroscopy. Thesize of cube-shaped PbS nanocrystals can be controlled by changing the relative amount ofPb(Ac)2·3H2O and dithioglycol. Smaller cube-shaped PbS nanocrystals were obtained at higher sulfurcontent in the reaction system. The nanometre-sized single crystals of PbS measure∼83 nm × 59 nm × 22 nm and 39 nm × 10 nm × 7 nm, for lead acetate:dithioglycol ratios of 1:0.375 (denoted as PbS-1) and1:1.5 (denoted as PbS-2), respectively, when a mixture of NaOH solutionof lead acetate and ethyl alcohol solution of dithioglycol is maintained at220 °C for 4 h in a Teflon-lined autoclave. XRD patterns and HRTEM images confirm thecrystalline structure of the PbS crystals. TEM helped to determine the dimension of thesingle crystals. Raman, XPS and IR helped to further demonstrate the purity of theas-synthesized samples. The optical absorption spectra of suspensions of the thesecrystals in glycol show shifts in absorption band edge for as-prepared sample PbS-1from 246 to 271 nm and for PbS-2 from 246 to 275 nm, after four days of storage,respectively. The photoluminescence peaks from the two samples are located at 434 and433 nm for photoexcitation radiation of 315–355 nm, thus exhibiting a Stokes shiftcompared with band edge energy. The principal contribution of this work is that thenanometre-size PbS single crystals are prepared without using a surfactant ortemplating agent. The formation of a five-membered ring via the chelation between thePb2+ ion and dithioglycol is considered to be crucial in this mechanism.