Designing\na Quantum Dot Upconversion Infrared Image\nSensor via a Photomultiplication Mechanism

The\nupconversion infrared (IR) image sensor selectively\nemits visible\nlight photons from the regions that have absorbed IR photons, allowing\nfor simplified manufacturing without the need for complex pixel integration.\nThese pixel-less upconversion IR image sensors enable low-cost, nondestructive\nimaging in the Internet of Things, security, and bioimaging applications,\nwhich include identifying blood circulation, tumors, and vascular\nstructures. Here we designed the material and structure of a quantum\ndot upconversion IR image sensor (QUIS) and achieved a photon-to-photon\nefficiency of 982% by inducing photomultiplication. A QUIS, designed\nwith an inverted structure for charge balance, uses Mg-alloyed ZnO\nnanoparticles as an electron transport layer to control the electron–hole\nratio. We analyzed the type and amount of charge present within the\nQUIS, elucidating the mechanism driving photomultiplication and the\norigin of photon-to-electron efficiency exceeding 100000%. The pixel-free\nQUIS is demonstrated as a bioimaging sensor by detecting human movement\nand blood pulse detection.