seminars

Triplet energy transfer from colloidal semiconductor nanocrystals to organic molecule for photo up-conversion application and relative mechanisms

Physical and Analytical Chemistry Seminar

Lecturer: Kaituo Dong, Schulich Faculty of Chemistry, Technion, group of Prof. Lilac Amirav

Date:
26-26 Jan 2021 @ 00:00 - 15:30

Location: Join Zoom Meeting at https://technion.zoom.us/j/98640529463

The ability to upconvert two low energy photons into one high energy photon has potential applications in optoelectronics, solar energy conversion, biological imaging, and data storage. Some semiconductor nanocrystals, like CdSe, PbS, PbSe or CsPbBr3, modified by the surface ligands, could combined with molecular emitters, such as rubrene and diphenylanthracene (DPA), to upconvert photons in both the visible and the near-infrared spectral regions. Absorption of low energy photons by the nanocrystals is followed by energy transfer to the molecular triplet states, which then undergo triplet−triplet annihilation (TTA) to create high energy singlet states that emit upconverted light.

The upconversion efficiency could be enhanced by exchange of the surface ligands with polyaromatic carboxylic acids on the nanocrystals to form an energy cascade or modification of sub-monolayer semiconductor. Surface modification could either facilitate the triplet energy transfer or suppress charge transfer from the nanocrystals to the surface ligands.

To observe the triplet energy transfer from semiconductor nanocrystals to the surface-anchored ligands, transient absorption spectroscopy was adopted, in which decay of the semiconductor nanocrystals excited state was observed, coinciding with the growth of triplet state absorption of surface ligands. Besides the above direct triplet-triplet energy transfer, there was another charge-transfer mediated triplet-triplet energy transfer, in which hole transfer first occurred to form the negative nanocrystals and positive ligands, then electrons transferred from nanocrystals to the positive ligands to form the triplet excited state in the ligands.

The investigation of mechanism of triplet energy transfer could pave the way for the rational design of the energetics at the semiconductor nanocrystals/surface organic ligands interface for triplet sensitization and photo upconversion application.