Photophysics and charge dynamics of Q-PbS based mixed ZnS/PbS and PbS/ZnS semiconductor nanoparticles

The surface of ZnS and PbS has been modified by interfacing PbS on ZnS and ZnS on PbS nanoparticles. This produced core–shell nanocomposites ZnS/PbS and PbS/ZnS with tunable electronic properties. In both structures PbS particles are present in cubic form with an average diameter of about 6 nm. The addition of Pb2+ (⩾3×10−4 moldm−3) to Q-ZnS (1.5×10−4 moldm−3) in the basic pH range produces size-quantized fluorescent PbS particles coated by metal hydroxides. In these particles the relaxation kinetics of charge carriers has been followed using a picosecond single-photon counting technique. At ⩽1.5×10−4 moldm−3 Pb2+ an interfacial relaxation of charge from ZnS to PbS phase could be observed in subnanosecond time domain. An increase in [Pb2+] from 2×10−42×10−4 to 1×10−3 moldm−3 enhanced the average emission lifetime from 9.4 to 19.4 ns. Composite PbS/ZnS particles are produced at high [ZnS] only. These particles had emission lifetime in μs time range. The extent of charge separation and the dynamics of charge carriers could be manipulated by the surface modification of these nanostructures.

Graphical abstractThe interfacing of Q-ZnS with PbS and Q-PbS with ZnS has been utilized to produce tailored PbS nanocomposites with tunable electronic properties. The addition of smaller amounts of Pb2+ to ZnS produces Q-PbS particles at its interface whereas at its higher concentrations Pb(OH)2/Zn(OH)2 coated luminescent PbS nanoparticles are produced. Lifetime measurements of these nanocomposites demonstrate a rapid relaxation followed by the slow relaxation of charge in ZnS and PbS phases, respectively. The separation of charge is enhanced in case of PbS/ZnS core–shell particles. This aspect may have promising applications in the areas of photophysics, photonics and photocatalysis.Figure optionsDownload full-size imageDownload as PowerPoint slide