Journal
ACS NANO
Volume 9, Issue 7, Pages 7097-7104Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.5b01717
Keywords
photoluminescence decay; radiative rate; nonradiative channel; lifetime; dispersion factor
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Funding
- Swedish Research Council (VR)
- Goran Gustafssons Foundation
- Natural Science and Engineering Council of Canada
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Spectrally resolved photoluminescence (PL) decays were measured for samples of colloidal, ligand-passivated silicon nanocrystals. These samples have PL emission energies with peak positions in the range similar to 1.4-1.8 eV and quantum yields of similar to 30-70%. Their ensemble PL decays are characterized by a stretched-exponential decay with a dispersion factor of similar to 0.8, which changes to an almost monoexponential character at fixed detection energies. The dispersion factors and decay rates for various detection energies were extracted from spectrally resolved curves using a mathematical approach that excluded the effect of homogeneous line width broadening. Since nonradiative recombination would introduce a random lifetime variation, leading to a stretched-exponential decay for an ensemble, we conclude that the observed monoexponential decay in size-selected ensembles signifies negligible nonradiative transitions of a similar strength to the radiative one. This conjecture is further supported as extracted decay rates agree with radiative rates reported in the literature, suggesting 100% internal quantum efficiency over a broad range of emission wavelengths. The apparent differences in the quantum yields can then be explained by a varying fraction of dark' or blinking nanocrystals.
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