Optimized Cation Exchange for Mercury Chalcogenide 2D Nanoplatelets and Its Application for Alloys

II-VI two-dimensional (2D) nanoplatelets (NPLs) exhibit the narrowest optical features among nanocrystals (NCs). This property remains true for Hg-based NPLs, despite a cation exchange procedure to obtain them from Cd-based NPLs, which leads to structural defects (poorly defined edges and voids) inducing inhomogeneous broadening. Here, we propose an optimized procedure for which a solvent, surface chemistry, and reaction conditions are rationally considered. The procedure is applied to the growth of alloyed HgSe1-xTex NPLs with various compositions. We report a bright photoluminescence for all compositions. Structural properties being now well defined, it is possible to study the electronic properties of these objects. To do so, we combine k.p modeling of quantum-confined structures with X-ray photoemission. In particular, we clarify the origin of the similarity between CdTe and HgTe NPLs absorption spectra despite their vastly differing bulk band structures. Finally, static- and time-resolved photoemission unveil a crossover from n- to p-type behavior in HgSe1-xTex NPLs while increasing the Te content.