Efficient exciton energy recycling and transfer in nanocrystals

A nonradiative Auger recombination of an exciton and an impact excitation by a highly energetic free carrier are two inverse manifestations of the same physical process. In nanocrystals two excitons may undergo Auger recombination, forming a single, high-energy electron-hole pair, while one of the “hot” carriers created in this process can induce a band-to-band excitation, reversing the Auger process. The sequential action of these events will continue as long as the excess energy of a hot carrier is sufficient to induce the impact excitation. In result, the effective lifetime of hot carriers and multi-exciton complexes may be enhanced. For Si nanocrystals this boosts hot carrier recombination and trapping and increases efficiency of energy transfer at nanoscale; in particular, RE ions in a direct vicinity of nanocrystals will be sensitized and exciton exchange between proximal nanocrystals may appear.

In my presentation, I will discuss these effects and compare the hot-carrier related energy exchange with that induced by FRET for ground-state excitons in Si and CsPbBr3 inorganic perovskite nanocrystals.  For the latter, I will show how the band structure, and in particular the bandgap energy of individual nanocrystals is altered when placed within ensemble. In that way coupling between proximal nanocrystals is directly visualized.

Date: 
Thursday, November 3, 2016 -
11:15 to 12:30
Location: 
Seminar room
Speaker: 
Tom Gregorkiewicz
Affiliation: 
UvA