Size and composition dependent multiple exciton generation efficiency in PbS, PbSe, and PbS(x)Se(1-x) alloyed quantum dots

Nano Lett. 2013 Jul 10;13(7):3078-85. doi: 10.1021/nl4009748. Epub 2013 Jun 20.

Abstract

Using ultrafast transient absorption and time-resolved photoluminescence spectroscopies, we studied multiple exciton generation (MEG) in quantum dots (QDs) consisting of either PbSe, PbS, or a PbSxSe1-x alloy for various QD diameters with corresponding bandgaps (Eg) ranging from 0.6 to 1 eV. For each QD sample, we determine the MEG efficiency, ηMEG, defined in terms of the electron-hole pair creation energy (εeh) such that ηMEG = Eg/εeh. In previous reports, we found that ηMEG is about two times greater in PbSe QDs compared to bulk PbSe, however, little could be said about the QD-size dependence of MEG. In this study, we find for both PbS and PbSxSe1-x alloyed QDs that ηMEG decreases lineally with increasing QD diameter within the strong confinement regime. When the QD radius is normalized by a material-dependent characteristic radius, defined as the radius at which the electron-hole Coulomb and confinement energies are equivalent, PbSe, PbS, and PbSxSe1-x exhibit similar MEG behaviors. Our results suggest that MEG increases with quantum confinement, and we discuss the interplay between a size-dependent MEG rate versus hot exciton cooling.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alloys
  • Computer Simulation
  • Energy Transfer
  • Lead / chemistry*
  • Luminescent Measurements / methods*
  • Materials Testing
  • Models, Chemical*
  • Particle Size
  • Quantum Dots*
  • Selenium Compounds / chemistry*
  • Sulfides / chemistry*
  • Surface Plasmon Resonance / methods*

Substances

  • Alloys
  • Selenium Compounds
  • Sulfides
  • lead selenide
  • lead sulfide
  • Lead