CdSe_<i>x</i>S_1–<i>x</i> Alloyed Nanoplatelets with Continuously Tunable Blue-Green Emission

Cadmium chalcogenide nanoplatelets (NPLs) are established as promising materials for a wide variety of optoelectronic applications due to their properties surpassing in many aspects their counterpart nanocrystals (NCs) with other shapes. Most of these features arise from strong quantum confinement in the direction of thickness which can be tuned with precision down to one monolayer. However, atomic smoothness of their basal planes and hence the ability to change the NPL thickness only in discrete steps prevent precise tuning of absorption and photoluminescence spectra unlike in the case of quantum dots. Preparation of alloyed NCs provides a potential solution to this problem, but it is complicated by the different reactivities of chalcogenide sources, which becomes even more restrictive in the case of NPLs because they are more sensitive to alterations of reaction conditions. In this work, we overcome this obstacle by employing highly reactive stearoyl sulfide and selenide as chalcogen sources, which enable straightforward variation of the NPL composition and thickness by changing the ratio of chalcogen precursors and reaction temperature, respectively. Alloyed CdSexS1–x NPLs obtained exhibit tunable absorption and photoluminescence bands covering the blue-green region from 380 to 520 nm with bright band-edge emission and quantum yields of ∼30–50% due to their relatively small lateral size enabled by a much finer control of the lateral growth