Near-infrared photon upconversion and solar synthesis using low-toxicity nanocrystals

Near-infrared to visible photon upconversion holds great promise for a diverse range of applications. Current photosensitizers for triplet-fusion upconversion across this spectral window often contain either precious or toxic elements, and have relatively low efficiencies. For example, although colloidal nanocrystals have emerged as versatile photosensitizers, the only family of nanocrystals discovered for near-infrared upconversion is the highly-toxic lead chalcogenides. Here we report zinc-doped CuInSe2 nanocrystals as a low-cost and low-toxicity alternate, allowing for near-infrared to yellow upconversion with an external quantum efficiency reaching 16.7%. When directly merged with photoredox catalysis, this system enables efficient near-infrared-driven organic synthesis and polymerization, which in turn solves the issue of reabsorption loss for nanocrystal-sensitized upconversion. Moreover, the broadband light capturing of the nanocrystals allows for rapid reactions under indoor sunlight, an especially remarkable example among which is polymerization of acrylates within just 30 seconds. Extending the reach of "solar synthesis" into the near-infrared may realize the century-long dream of conducting high added-value chemical transformations using sunlight.