Nanoscale physics
Excitonic energy transfer in close-packed ZnSe quantum dots films stabilized by 1-thioglycerol
 Bondar N.V.1a, M.S. Brodyn1.
1 Departament of nonlinear optics, Institute of Physics of NASU, Ukraine.
Prospect Nauki, 46, Kyiv-03039, Ukraine. 
1a E-mail: nanodot50@gmail.com
We investigated optical properties of colloids and close-packed film ZnSe QDs with ~ (10-12)% size dispersion stabilized by thioglycerol (TG) through both steady-state (an absorption, PL and PLE spectra) and time-resolved spectroscopy experiments. The ET dynamics of excitons in ZnSe QDs arrays by measuring time- and spectrally resolved PL intensities shown the high efficiency of interdot ET, ~ (0.7 – 1.9) ns, on the blue-red sides of the PL band. It is also shown that the slowing down of the ET speed in close-packed QDs films is due to repeatedly of exciton hopping toward QDs of lower energy. As a result, they reaching of QDs with some an specific energy and a radius, which we called blocking QDs, where the ET process changes and excitons can only decay radiatively or nonradiatively and can be trapping on surface (defective) states. In this work we also shown that a steady-state and time-resolved spectroscopic evidence the electronic ET in close-packed ZnSe QD films arising from dipole-dipole inter-QDs interactions between proximal QDs and an effect of ligands on the core states of ZnSe QDs by electrostatic compression of the electron wave function. We observe that in close-packed ZnSe QDs films stabilized by thioglycerol, the ET time constant can be as fast as 750 ps and although these values is deficient for suppressed Auger processes [1], they provides a path for accelerating ET and exciton migration between donor-acceptor pairs by minimizing ligand length (an exciton bridges) or decreasing the potential barrier between proximal QDs. Two possible a models restricted to the ET process and the diffusion length of excitons in films were suggested and quantified, including blocking QDs with an specific energy and a radius. Thus predicting ET between QDs at small distances within a close-packed ZnSe QDs film requires further understanding of excitonic ET in QD films relevant for optoelectronic devices such as light-harvesting complexes and solar cells [2].
    
     1. S. A. Crooker, J. A. Hollingsworth, S. Tretiak, V. I. Klimov // Phys. Rev.
       Lett.- 2002. - 89. - P. 186802.
2. C. Wang, E. A. Weiss. // Nano Lett. -2017. - 17.- P. 5666–5671.