Effect of Sn concentration on optical and structural properties of Pb_1-xSn_xS nanopowder

Department of Physics, University of Golestan, Gorgan 49138-15739, Iran

^a e-mail: r.lotfiorimi@gu.ac.ir

Received: 15 April 2014
Revised: 23 June 2014
Accepted: 25 June 2014
Published online: 8 August 2014

Abstract

Pb_1-xSn_xS nanopowder with different Sn concentrations (x = 0.02, 0.05, 0.10, 0.20, 0.50 and 1.00) were synthesized by chemical precipitation route under N₂ atmosphere. The samples were characterized by X-ray diffraction(XRD), UV-vis absorption spectra and photoluminescence (PL) spectra. The XRD results show that the samples with 0 ≤ x ≤ 0.2 have cubic (fcc) structure with diameter in the 12.8–24 nm range. The sample with x = 0.5 has orthorhombic structure with a diameter of 9.2 nm. The band gap (or absorption edge) of PbS exhibits a large blue shift when the crystallite size is reduced to nanometer scale, from 0.4 eV in bulk samples to 1.8 eV in nanosize samples, which can be related to large Bohr excitonic radius of PbS nanoparticles. PL emission spectra of Pb_1-xSn_xS in red region excited at 315 nm, for x = 0 showed three broad peaks located at 776.5 nm, 809 nm and 826 nm which due to the defect densities and for x = 0.02, 0.05, 0.10 there are two relatively strong emission peaks located at 786 nm and 823 nm which can be related to transition from sulfur vacancy level and Sn⁺² ion level respectively.