Proceedings of September Meeting 2016 (NFM16)
Publication date: 14th June 2016
General features of the delayed emission in CdSe core (CdS shell) nanocrystals, from 0-D to 2-D: The time-resolved photoluminescence of 0-D1, 1-D2, and 2-D3 CdSe (core)/CdS (shell) nanocrystals show a number of common features: (1) After a short exponential decay in the first tens of ns, the decay follows a power law, i.e. I(t) is proportional to t-a; where a is the power-law exponent between 1.5 and 2, depending on the system. This power law is valid up to the longest time that we could detect photons with our sensitive detector. (2) The spectrum of the CdSe nanocrystals (0-D, 2-D) does not change over the time range of the delayed emission. This indicates that the delayed emission is coming from an unperturbed single exciton. It hence means that the exciton can be “stored” in an optically inactive state over variable periods before transition to the optically active state. (3) We also measured the delayed luminescence on individual 0-D CdSe/CdS quantum dots and observed that there is delayed emission on the level of a single dot. (4) Moreover, the value for the power-law exponent is similar to those for the on- and off- periods of the blinking statistics of individual CdSe/CdS dots of the same batch. This is a strong indication that there is a single mechanism underlying the delayed emission and blinking. (5) We also found that the relative fraction of delayed emission decreases with increasing refractive index, showing that the bifurcation between the delay process and photon emission occurs on the level of the single exciton. We present a model in which an exciton can undergo reversible transitions between the emitting and “optically inactive” states (e.g. by trapping/detrapping of one of the carriers).
REFERENCES:1 Rabouw, F. T.;Kamp, M.;van Dijk-Moes, R. J. A.;Gamelin, D. R.;Koenderink, A. F.;Meijerink, A.;Vanmaekelbergh, D. Delayed Exciton Emission and Its Relation to Blinking in Cdse Quantum Dots. Nano Lett. 2015, 15, 7718-7725.2 Rabouw, F. T.;Lunnemann, P.;van Dijk-Moes, R. J. A.;Frimmer, M.;Pietra, F.;Koenderink, A. F.;Vanmaekelbergh, D. Reduced Auger Recombination in Single Cdse/Cds Nanorods by One-Dimensional Electron Delocalization. Nano Lett. 2013, 13, 4884-4892.3. Rabouw, F. T., et al., Temporary Charge Carrier Separation Dominates the Photoluminescence Decay Dynamics of Colloidal CdSe Nanoplatelets." Nano Letters 16(3): 2047-2053.
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