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From Visible to Infrared Emitters 2D Nanoplatelets

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2D colloidal nanoparticles, called nanoplatelets, have attracted attention in the last couple years. Cadmium chalcogenides nanoplatelets exhibit improved optical features such as narrow photoluminescence linewidth thanks to the atomic control of their confinement direction (i.e. no inhomogeneous broardening). All the three cadmium chalcogenides have been synthesized with a zinc blende structure and at least three different thicknesses from 2 to 4 monolayers. It is then possible to tune their emission properties either by growing core/crown heterostructures (lateral growth), or core/shell heterostructures (thickness growth). In core/crown nanoplatelets, a type I band alignement obtain for CdSe/CdS leads to an increase of the emission quantum yield. While in type II CdSe/CdTe we observe a broad emission in the near infrared (NIR) with a large Stoke shift compare to the absorption. It is now possible to obtain NPLs which absorbs and emits in the NIR . In order to reach this region, we use cation exchange on cadmium chalcogenides NPLs. Indeed, cation exchange is a way to reach compositions of nanoplatelets which cannot be directly synthesized. Thus HgTe and HgSe nanoplatelets have been obtained. HgTe NPLs present emission features in the near infrared range with a full width at half maximum at least two times thinner than the classical emitters in that range. In addition their photoluminescence lifetime is of 55ns for a quantum yield of 10%. These new materials are promising for a large variety of applications spanning from photovoltaic to the design of colloidal topological insulators.

This talk is part of the Optoelectronics Group series.

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