Ligand Enhanced Upconversion of Near-Infrared Photons with Nanocrystal Light Absorbers
Journal Article - Open Access
Department of Chemistry Riverside United States
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We designed and synthesized a tetracene derivative 4-tetracen-5-ylbenzoic acid CPT as a transmitter ligand used in PbSPbSe nanocrystal NC sensitized upconversion of near infrared NIR photons. Under optimal conditions, comparing CPT functionalized NCs with unfunctionalized NCs as sensitizers, the up conversion quantum yield QY was enhanced 81 times for 2.9 nm PbS NCs from 0.021 to 1.7 , and11 times for 2.5 nm PbSe NCs from 0.20 to 2.1 . The surface density of CPT controls the solubility of functionalized NCs and the upconversion QY. By increasing the concentration of CPT in the ligand exchange solution, the number of CPT ligand per NC increases. The upconversion QY is maximized at a transmitter density of 1.2 nm2 for 2.9 nm PbS, and 0.32 nm2 for 2.5 nm PbSe. Additional transmitter ligands inhibit photon upconversion due to triplet triplet annihilation TTA between two neighboring CPT molecules on the NC surface. 2.1 is the highest reported QY for TTA-based photon upconversion in the NIR with the use of earth-abundant materials.