Charged facets of a nanocrystal can form an intrinsic nanometer-size electric dipole. When the spacing between these nano dipoles is adjusted, the dipolar interaction energy is tuned from a fraction to a multiple of the thermal energy. Consequently, the onedimensional oriented attachment can be switched on or off, as is the growth of nanorods. This kinetically controlled growth is achieved at relatively low reaction temperatures while the thermodynamically controlled growth dominates at higher temperatures. The synthesized PbSe nanorods are branchless, exhibiting a single-exponential photoluminescence decay trace with an e-folding lifetime of 1.3 μs and a photoluminescence quantum yield of 35%.
Acetic acid causes branching of PbSe nanorods during the synthesis of colloidal PbSe nanorods. Removing acetic acid in the reaction solution prevents branching, resulting in uniform nanorods. It increases the photoluminescence quantum yield of the nanorods from 11% (branched) to 38% (branchless). The branchless nanorods exhibit single-exponential photoluminescence decay with a decay constant of 1.3 μs, in contrast to multiple-exponential photoluminescence decay in branched nanorods with an e-folding lifetime of 0.12 μs. The diameter of the nanorods can be tuned from 3.9 to 5.8 nm by changing the reaction temperature, resulting in an energy gap tunable from 0.88 to 0.65 eV. The dependence of the energy gap on the diameter follows the power law: diameter −1.5 . The superior optical properties, including long exciton lifetime, high photoluminescence quantum yield, and tunable energy gaps, make the branchless PbSe nanorods an excellent candidate material for thermoelectric and optoelectronic devices.
The student who drafted the manuscript was not aware of this contribution, and L.S. did not check the authorship carefully enough at the time of the manuscript submission. Therefore, Shailendra Chiluwal was missing in the authorship. However, he made significant contributions to this paper. A few figures (Figures 1 and S2− S4) are based on his work. He deserves to be the second author of this paper.
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