Sub-bandgap emission and intraband defect-related excited-state dynamics in colloidal CuInS2/ZnS quantum dots revealed by femtosecond pump–dump–probe spectroscopy

Kraatz, Ingvar and Booth, Matthew and Whittaker, Benjamin and Nix, Michael and Critchley, Kevin (2014) Sub-bandgap emission and intraband defect-related excited-state dynamics in colloidal CuInS2/ZnS quantum dots revealed by femtosecond pump–dump–probe spectroscopy. The Journal of Physical Chemistry C, 118 (41). pp. 24102-24109. ISSN 1932-7447

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Abstract

We consider the highly radiative, long-lived photoluminescence (PL) component observed in colloidal CuInS2/ZnS core/shell quantum dots (CIS/ZnS QDs) and provide evidence of the involvement of intragap defect states in the emission, settling a long ongoing discussion in the literature. Femtosecond transient absorption (fs-TA) spectroscopy was used to investigate subpicosecond dynamics in these technologically important QDs. Spectral and kinetic analysis of the fs-TA data, in combination with femtosecond pump–dump–probe experiments, revealed a stimulated emission component in CIS/ZnS QDs for the first time. PDP experiments showed that the excited-state absorption signal, originating from the conduction band (CB), was immune to the depopulation of the emitting state by a third, “dump” laser centered close to the luminescence maximum. We conclude that the optical transition responsible for the observed room-temperature PL in CIS/ZnS QDs does not originate from the CB as postulated in the literature but rather from high-lying intraband donor states most likely associated with indium–copper antisite defects. Filling of the emitting sub-bandgap state was assigned with a time constant of 0.5 ps, and de-excitation via remaining surface states was associated with a 1.8 ps time constant. A third longer decay constant (27 ps) was attributed to Auger recombination.

Keywords:Qauntum Dots, Copper Indium Disulfide, Transient Absorption Spectroscopy, Excited State Dynamics, NotOAChecked
Subjects:F Physical Sciences > F200 Materials Science
F Physical Sciences > F321 Solid state Physics
Divisions:College of Science > School of Mathematics and Physics
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ID Code:25264
Deposited On:26 Nov 2016 18:37

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