Electron migration limits the rate of photobrightening in thin films of cdse quantum dots in a dry N2 (g) atmosphere

Daniel B. Tice, Matthew T. Frederick, Robert P. H. Chang, Emily A Weiss

Research output: Contribution to journalArticle

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Abstract

This paper describes a study of the mechanism of photoinduced photoluminescence enhancement, termed "photobrightening" (PB), of ∼150-nm-thick films of CdSe quantum dots (QDs) in a dry N2 (g) atmosphere. Steady-state photoluminescence (PL) and ultrafast transient absorption measurements of films photoexcited continuously and shot-wise revealed that: (i) PL enhancement occurred in all of the close-packed films during periods of continuous photoexcitation and continued after the excitation source was turned off; (ii) the time-dependence of PB (both during excitation and in the dark) was initially linear and became exponential as the PB reached saturation; (iii) the rate of PB and the maximum PB achieved by the film depended on the degree of surface passivation of the QDs; (iv) the PL peak shifted to lower energy and broadened during PB; and (v) rates of nonradiative trapping of excitonic electrons decreased during PB. These data were utilized to construct a model for PB based on migration of photoexcited electrons within the film. The basis for this model is that PB is limited by the rate of migration of electrons among surface-localized energetically shallow traps in the film, and not by the rate of creation of surface-trapped charge carriers. The migration mechanism provides a rationalization for the seemingly contradictory reports that charging of QD surfaces causes PB in ensembles of QDs but causes photodarkening and blinking in single QDs.

Original languageEnglish
Pages (from-to)3654-3662
Number of pages9
JournalJournal of Physical Chemistry C
Volume115
Issue number9
DOIs
Publication statusPublished - Mar 10 2011

Fingerprint

Semiconductor quantum dots
quantum dots
Photoluminescence
atmospheres
Thin films
Electrons
photoluminescence
thin films
electrons
Photochromism
blinking
augmentation
Photoexcitation
causes
Charge carriers
photoexcitation
Thick films
Passivation
passivity
shot

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

Electron migration limits the rate of photobrightening in thin films of cdse quantum dots in a dry N2 (g) atmosphere. / Tice, Daniel B.; Frederick, Matthew T.; Chang, Robert P. H.; Weiss, Emily A.

In: Journal of Physical Chemistry C, Vol. 115, No. 9, 10.03.2011, p. 3654-3662.

Research output: Contribution to journalArticle

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