Semiconductor Pb2P2S6 and size-dependent band gap energy of its nanoparticles

Abstract

Microcrystalline Pb₂P₂S₆ powder was synthesized via a traditional melting salt method with KI or LiBr/KBr mixture (mole ratio is 3/2) acting as flux. The nanostructured Pb₂P₂S₆ powder was further synthesized by a high-speed ball milling technique. The Pb₂P₂S₆ powder was investigated by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), optical absorption (UV-vis) and photoluminescence measurements. The average particle size of the nanostructured Pb₂P₂S₆ powder changes from 500 to 60 nm when increasing the milling time from 0.5 h to 4 h. The optical properties of the Pb₂P₂S₆ powder show a size-dependence, with the band gap ranging from 2.56 eV to 2.88 eV. First-principle calculation reveal that the Pb₂P₂S₆ is a semiconductor with an indirect band gap of 2.15 eV. The size-dependent nature also makes the photoluminescence properties of the material tunable.