Structural, optical and electrical characterization of Mn2+ and Cd2+ doped/co-doped PbS nanocrystals

The strain and stress minimized nanoparticles of PbS, Pb0.95Mn0.05S, Pb0.95Cd0.05S and Pb0.90Mn0.05Cd0.05S were successfully synthesized using solvothermal microwave irradiation (SMI) method. The quality/performance of the materials was found to be in the series Pb0.90Mn0.05Cd0.05S > Pb0.95Cd0.05S > Pb0.95Mn0.05S > PbS. The average crystallite size in the best material Pb0.90Mn0.05Cd0.05S was found to be ∼18 nm where the particles are distributed within the range 20-60 nm. Optical studies reveals the existence of direct band gap in the range of 2.025-2.235 eV (±0.012 eV). This is one of the widest Eg values reported for this system. Electrical measurements were performed on compacts of nanoparticles in the temperature range 313-433 K and frequency range 100 Hz-1 MHz. The conductivity profile exhibits two components; in which the activation energy (ΔE) values obtained for the temperature range 373-433 K is almost twice as compared to the ΔE value obtained for 313-373 K. Nonetheless, the conductivity at the higher temperatures was always higher than at the low temperatures and interestingly, the nanoparticles exhibits higher conductivity than their bulk counterpart. The feasible mechanism of conduction is discussed.