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The Effect of Dispersion Media on Photoluminescence of Colloidal CdSe Nanocrystals Synthesized from TOP

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journal contribution
posted on 17.05.2005 by Kui Yu, Badruz Zaman, Shanti Singh, Dashan Wang, John A. Ripmeester
The media used for dispersion have a significant effect on the photoluminescent (PL) efficiency of colloidal CdSe nanocrystals, in addition to synthetic parameters. The investigated dispersion media were water-insoluble hexanes (Hex), toluene (Tol), chloroform (CHCl3), and water-miscible tetrahydrofuran (THF); in addition, a water−THF mixture (25%, weight), a tri-n-octylphosphine (TOP)−Hex mixture (25%, weight), and a TOP−THF mixture (25%, weight) were also explored as dispersion media. Solvent-dependent equilibriums affect the number of surface-adsorbed molecules available for surface passivation and the removal of surface ligands, with both concentration and additives (such as TOP) and time playing a role, so that PL intensities can either be enhanced or diminished depending on the detailed conditions. Moreover, an enhancement is not possible at low concentrations of nanocrystals after days of storage, as dissociation of the surface ligands plays a major role and leads to the formation of the other fluorescent species causing baseline uprising. The colloidal CdSe nanocrystals used were synthesized in a reaction medium consisting of tri-n-octylphosphine (TOP), with cadium oxide (CdO) as the Cd precursor and TOPSe as the Se source.