Sonochemical-assisted preparation of mesoporous ZnS quantum dots: Optical, electrical, and temperature-dependent dielectric characteristics

Abstract

Mesoporous ZnS quantum dots (QDs) were prepared by the sonochemical technique that indicated bi-structural cubic-hexagonal phases with an average particle size of 2.5 nm, a pore size of 4 nm, and 28.85 m2 g−1 surface area. ZnS QDs exhibited a high bandgap of 3.85 eV with a large Urbach energy of 280 meV. The presence of localized defects was verified by the photoluminescence emission that was ascribed to the recombination of trapped carriers in shallow and deep trapping states with photogenerated holes. ZnS QDs revealed a high DC conductivity of 5.37 × 10−6 Ω−1 m−1 and a small activation energy of 248 meV that facilitated the tunnelling of thermionically excited carriers. The frequency-dependent behavior of AC conductivity (σAC), dielectric constant (εr), and dielectric loss (ε′) was examined at various temperatures. It was observed that both σAC, εr, ε′ were enhanced with increasing temperature up to 333 K followed by a gradual decrease at higher temperatures.