Spectroscopy of Colloidal Quantum Dots: Suppression of Photoluminescence Blinking in Giant Nanocrystals.

Anton V. Malko

The University of Texas at Dallas

Colloidal nanocrystals (NCs) have been at the forefront of the optoelectronics research since their initial discovery by Brus and co-workers. Strong research efforts have been applied to understand and engineer dynamics of multiexciton (MX) states in such NCs, specifically to address carrier multiplication and PL fluorescence intermittency (blinking) issues. Recently1, we developed a new class of "giant" CdSe/CdS multishell nanocrystals of CdSe cores overcoated with multiple layers of inorganic shells (CdS) and observed complete blinking suppression at time scales from milliseconds to minutes for dots with n>12 monolayers of CdS. In single dot PL measurements of such g-NCs we observed MX emission in steady-state PL at low (10 K) temperatures2. By analyzing steady-state and time-resolved PL traces we found that rates of Auger non-radiative recombination for MXs can be much less their radiative rates, allowing for significant fraction of multiexcitons to recombine radiatively.3 We also suggested that Auger rates for charged excitons (trions) depend crucially on carrier localization length and observed large differences for recombination rates of negative and positive trions. These observations allowed us to propose an ingenuous mechanism that explains observed blinking suppression.4

[1] JACS 130(15), 5026 (2008);

[2] Nano Letters, 10(7), 2401-2407 (2010);

[3] Phys. Rev. Lett. 106, 187401 (2011);

[4] Nano Letters 11, 5213 (2011)