Synthesis of Thick Hg_<em>x</em>Cd_{1–<em>x</em>}Se Nanoplatelets by Cation Exchange Catalyzed by Silver Ions, Showing Amplified Spontaneous Emission

II-VI semiconductor nanoplatelets have emerged as promising candidates for various applications, owing to their tunable optical properties dictated by their thickness and compositions. In the realm of infrared technology, mercury chalcogenides stand out as particularly promising materials for optoelectronic applications. However, the direct synthesis of 2D particles in this category remains challenging, thus prompting the exploration of alternative methods such as cation exchange. Here, we demonstrate that the cation exchange process from cadmium to mercury can be effectively catalyzed by monovalent Ag⁺ cations. Further, this catalysis facilitates the formation of alloyed Hg_xCd_1-x Se nanoplatelets with tunable optical properties, with the photoluminescence peak ranging from 1.23 eV for the thinnest three-monolayer (ML) nanoplatelets to 0.92 eV for the thickest 7 ML nanoplatelets. The Ag⁺ ions reduce the activation energy of the cation exchange process by a factor of 2, enabling enhanced penetration of mercury atoms deep into the native CdSe nanoplatelets. Moreover, these nanoplatelets exhibit optical gain in the infrared spectrum, including the 1.3 μm telecommunication band, with a fluence threshold at 80 K of 50 μJ∙cm^-2.. Authors: Fu, Ningyuan [Ecole Superieure de Physique et de Chimie Industrielles (ESPCI), ParisTech (France); PSL Research University (France); Sorbonne Univ., Paris (France); Centre National de la Recherche Scientifique (CNRS) (France)] (ORCID:0000000162313991); Lehouelleur, Henri [Ecole Superieure de Physique et de Chimie Industrielles (ESPCI), ParisTech (France); PSL Research University (France); Sorbonne Univ., Paris (France); Centre National de la Recherche Scientifique (CNRS) (France)]; Makké, Lina [Ecole Superieure de Physique et de Chimie Industrielles (ESPCI), ParisTech (France); PSL Research University (France); Sorbonne Univ., Paris (France); Centre National de la Recherche Scientifique (CNRS) (France)]; Curti, Leonardo [Ecole Superieure de Physique et de Chimie Industrielles (ESPCI), ParisTech (France); PSL Research University (France); Sorbonne Univ., Paris (France); Centre National de la Recherche Scientifique (CNRS) (France)] (ORCID:0009000294511647); Dabard, Corentin [Ecole Superieure de Physique et de Chimie Industrielles (ESPCI), ParisTech (France); PSL Research University (France); Sorbonne Univ., Paris (France); Centre National de la Recherche Scientifique (CNRS) (France)] (ORCID:0000000312146026). DOE Contract: AC02-06CH11357. Subjects: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Cadmium selenide; Ion exchange; Mercury; Mixtures; Nanoparticles