PbS and PbSe quantum dots (QDs) are promising strong infrared emitters. We have developed several synthetic routes to producing PbS and PbSe QDs with a variety of sizes such that the bandgap can be continuously tuned from 2000 to 1000 nm. We provide a simple and accurate synthetic route to reproducibly produce PbS QDs with a narrow size-distribution and high chemical yield. The different synthetic routes lead to differences in their surface chemistry and to differences in their air stability and photoluminescence quantum yields (PLQY). To characterize the PLQY we directly measured the PLQY IR-26 (a standard IR emitting organic dye) at a range of concentrations as well as the PLQY of PbS and PbSe QDs for a range of sizes. We find that the PLQY of IR-26 has a weak concentration dependence due to reabsorption, with a PLQY of 0:048_0:002% for low concentrations, lower than previous reports by a full order of magnitude. We also find a dramatic size dependence for both PbS and PbSe QDs, with the smallest dots exhibiting a PLQY in excess of 60% while larger dots fall below 3%. A model, including nonradiative transition between electronic states and energy transfer to ligand vibrations, appears to explain this size dependence. These findings provide both a better characterization of photoluminescence for near infrared emitters. Halogen surface passivation provides both a larger PLQY (~ 30% improvement) as well as increased air stability.
Matthew C. Beard, Octavi E. Semonin, Justin C. Johnson, Ashley Marshall, Jianbing Zhang, and Boris D. Chernomordik, "Photoluminescence quantum yields of PbSe and PbS QDs in the range of 1000 nm to 2000 nm
(Conference Presentation)," Proc. SPIE 9723, Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications VIII, 97230F (Presented at SPIE BiOS: February 15, 2016; Published: 27 April 2016); https://doi.org/10.1117/12.2211728.4848770178001.
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