Stable Infrared-Emitting Chemical Composition Gradient Quantum Dots for Down-Convertors and Photodetectors

Though remarkable breakthroughs have been made in visible-light-emitting quantum dots (QDs), the high potential in optoelectronic applications for efficient and stable infrared (IR)-emitting QDs has yet to be largely explored. The major obstacle for commercialization of these low-bandgap nanomaterials lies in their low chemical stability in ambient environments and difficulties in tuning and retaining the targeted optical characteristics. Herein, we report on a well-controlled yet facile cation-exchange strategy for crafting core/graded shell/shell QDs with precisely tailored spatial compositions to accurately regulate the optical properties in the IR region while simultaneously enhancing stability by utilizing CdSe/Cd1-xZnxSe1-ySy/ZnS QD nanotemplates. PbSe/PbSe1-ySy/PbS QDs with tailored dimensions are yielded via a simple yet robust cation-exchange process that effectively replaces the Cd and Zn cations with the cation of interest (i.e., Pb) without disrupting the anionic framework. The absorption and emission of IR QDs can be precisely altered from 1200 to 2500 nm by either controlling the cation exchange time or tuning the dimensions and optical wavelengths of the inorganic nanotemplate (i.e., CdSe/Cd1-xZnxSe1-ySy/ZnS QDs). These IR QDs manifest excellent colloidal stability in solution for months. Moreover, absorption wavelengths are well retained for more than 50 days without any noticeable shifts. Such a cation-exchange route is simple yet robust and may render the creation of a large variety of stable IR QDs of interest in a rapid and controllable manner for applications in IR-emitting down-converters, lasers, photodetectors, sensors, and so on.