We will present results on luminescence quenching and enhancement in metal sulfide nanoparticles, with a focus on PbS. Bare PbS and ZnS- and Pb(OH)2-capped PbS nanoparticles produced in inverted micelles luminesce extremely weakly. Removal of water present during synthesis results in a significant increase in the luminescence quantum yield of the nanoparticles. The band edge emission maximum is near 800 nm for core-shell nanoparticles with mean diameters of 3.4 nm. Dried and Pb(OH)2-capped PbS nanoparticles are produced with quantum yields >3%. Water addition to the dried nanoparticles induces efficient luminescence quenching for both uncapped and capped particles. KSV for bare PbS is 140 M-1, compared with 92 M-1 and 47 M-1 for ZnS- and Pb(OH)2-capped PbS, respectively. H2O and D2O quench the luminescence of the dried particles with similar efficiencies. Methanol and other alcohols do not quench the PbS luminescence. Quenching of luminescence with water is also observed for HgS and Cd(OH)2-capped CdS nanoparticles. We propose a quenching model where water penetrates into the nanoparticle crystal lattice.
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