Isolation of Bright Blue Light-Emitting CdSe Nanocrystals with 6.5 kDa Core in Gram Scale: High Photoluminescence Efficiency Controlled by Surface Ligand Chemistry

Alkylamine-capped blue light-emitting (CdSe)34 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)34 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 31P and 1H 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.