Colloidal semiconducting nanoplatelets (NPLs) have drawn massive attention because of their unique optical characteristics, such as narrow emission peak, low Stokes shift, large oscillator strength, and deterministic in-plane radiating dipoles. Many applications can be better realized once the excitonic properties of both single and close-packed NPLs are understood. In my thesis, I studied the photophysics of self-assembled linear platelet chains, an interesting system of highly ordered collective nano-emitters, by micro-photoluminescence experiments and numerical simulations. I obtained two main results :
Transition dipole components in single or stacked NPLs were precisely probed by a protocol combining polarimetry, Fourier-plane imaging, photon correlation measurements and decay analysis. An emerging out-of-plane dipole component was demonstrated in the assembled chains of NPLs, which is absent in the single non-stacked platelets. This observation suggested the mechanical interaction between NPLs in the assembly.
Long range (500 nm) excitonic energy transfers (FRET) in platelet chains were demonstrated by micro-photoluminescence. A homo-FRET time of 1.5 ps between platelets was extracted from a diffusion equation model, which is faster than other excitonic processes in nanoplatelets, such as radiative recombination, Auger recombination and quenching by defects. Thus, it can be expected that the ultrafast FRET will significantly modify the excitonic property of assembled emitters as compared to isolated ones.
Jury
Mme. Sophie Brasselet (Institut Fresnel, Marseille, rapportrice)
M. Stephane Berciaud (Université de Strasbourg, rapporteur)
