Abstract
The oxidation speed of PbS quantum dots has been a subject of controversy for some time. In this study, we reveal the precise functional form of the oxidation rate constant for bare quantum dots through analysis of their photoluminescence as a function of temperature, oxygen pressure, and excitation-laser intensity. The combined effect of these factors results in a reduced energy barrier that allows the oxidation to proceed at a high rate. Each absorbed photon is found to have a 10−8 probability of oxidizing a PbS atomic pair. This highlights the importance of photo-excitation on the speed of the oxidation process, even at low illumination conditions. The procedure used here may set up a quantitative standard useful for characterizing the stability of quantum dots coated with ligands/linkers, and to compare different protection schemes in a fair quantitative way.
Highlights
Lead sulfide (PbS) quantum dots (QDs) continue to be a material of large scientific and technological interest due their size-dependent optical properties
Peterson et al [13] found that the photo-oxidation rate of PbS quantum dots was size dependent; this is a very interesting result, but the QDs studied were oleic acid coated and embedded within a polymer, which made the gas-QD surface interaction hard to describe in a quantitative way
Because most of these discrepancies could be traced to non-trivial differences in testing conditions and QDs cappings, to have a clear relationship between light, gas pressure, temperature, and the rate of change at the surface of PbS quantum dots, we propose it is necessary to test the evolution under those environmental variables in non-aggregated ligand-free PbS QDs, with the goal of arriving to precise quantitative reaction rates
Summary
Lead sulfide (PbS) quantum dots (QDs) continue to be a material of large scientific and technological interest due their size-dependent optical properties. Et al [11] showed that ethanedithiol-treated PbS QDs in films will oxidize, ripen, and even sinter Because most of these discrepancies could be traced to non-trivial differences in testing conditions and QDs cappings, to have a clear relationship between light, gas pressure, temperature, and the rate of change at the surface of PbS quantum dots, we propose it is necessary to test the evolution under those environmental variables in non-aggregated ligand-free PbS QDs, with the goal of arriving to precise quantitative reaction rates. Under illumination, the temperature of the environment was played a significant role, with an apparent activation energy barrier of only 0.19 eV These findings, obtained from easy-to-follow changes in the PL emission under controlled conditions, are significant because they highlight the key role that photo-excitation performs in the material transformation process and the substitutive roles that O2, light intensity, and temperature can play in the oxidation of PbS QDs
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