Isolation of Bright Blue Light-Emitting CdSe Nanocrystals
with 6.5 kDa Core in Gram Scale: High Photoluminescence Efficiency
Controlled by Surface Ligand Chemistry
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Abstract
Alkylamine-capped
blue light-emitting (CdSe)<sub>34</sub> nanocrystals
were synthesized via a phosphine-free method and isolated in gram-scale
quantity. The exclusive formation of 6.5 kDa core mass was confirmed
by combined optical spectroscopy and high resolution mass spectrometry
studies. Variable power laser desorption ionization-mass spectrometry
further confirmed the formation of the (CdSe)<sub>34</sub> core. The
surface ligand chemistry was found to be extremely important in enhancing
the photoluminescence properties. The nanocrystals were highly stable
during the postsynthetic ligand treatment with triphenylphosphine,
which increased their fluorescent quantum yield up to 23.6% without
compromising the core composition as determined by mass spectrometry.
Examination of their <sup>31</sup>P and <sup>1</sup>H NMR spectra
demonstrated the presence of amine and phosphine on the surface of
the nanocrystals where phosphines were selectively attached to surface
selenium sites that stabilized the nonradiative trap states and increased
the fluorescence quantum yield. The gram-scale synthesis and high
quantum yield of single-sized nanocrystals should greatly facilitate
new and improved semiconductor nanocrystal applications in the field
of nanoscience and nanotechnology, resulting in more rapid and less
expensive production of future advanced electrochromic and light-emitting
devices