Ag₂ZnSnS₄–ZnS core–shell colloidal quantum dots: a near-infrared luminescent material based on environmentally friendly elements

Abstract

Low cost, multinary colloidal quantum dots (QDs) based on environmentally friendly elements, with bright, narrow-width, tunable near-infrared (NIR) luminescence are promising alternatives to Cd and Pb chalcogenide QDs for <i>in vivo</i> bio-imaging, LED and sensing applications. Herein, we demonstrate Pb/Cd free solution-processed colloidal luminescent Ag₂ZnSnS₄-ZnS (AZTS-ZnS) core-shell QDs with precise control over the ZnS shell thickness and thereby its optical properties. Unlike indium based multinary (I-III-VI group) core-shell QDs these nanocrystals show a narrow photoluminescence (PL) full width at half maximum (fwhm) of 105-110 meV in the first NIR window. By monitoring the starting AZTS core size, we achieve tunable emission over a small NIR window in these QDs with the best PL quantum yield (PLQY) of 17.4%.