DEVELOPING EFFICIENT COLLOIDAL QUANTUM DOT-BASED NEAR-INFRARED TO VISIBLE PHOTON UPCONVERTER

Abstract

NIR light can be converted into higher energy visible light by a process called photon up-conversion. The development of efficient photon upconverters is crucial for a varied range of applications like thermal imaging, bioimaging, night vision, surveillance, photovoltaics, photocatalysis, IR camera, etc. There are several methods and related recognized processes exist that show photon up-conversion. Among these processes, colloidal quantum dots (CQDs) sensitized up-conversion via Triplet-Triplet annihilation (TTA) have made significant progress in recent years as potential materials for successful photon due to their broad absorption spectrum in NIR region. This system generally consists of a sensitizer that absorbs lower energy photons and an emitter that emits higher energy photons through TTA. For efficient NIR to visible upconverters, lead sulphide (PbS) CQDs are chosen as sensitizer because of their active bandgap variation in the NIR region via size tuning due to the strong quantum confinement effect; hence, it becomes a good choice for infrared sensitizers that can absorb the NIR photons and transfer them to the emitters. Despite their high absorption coefficient, the PbS CQD as sensitizers in TTA-based up-conversion shows low photoluminescence quantum yield (PLQY) due to non-radiative recombination in the material. A high PLQY of the sensitizer material is desirable for efficient photon up-converters. Electron-rich materials like ZnO nanocrystals incorporation inside PbS CQD-based matrix improved the PLQY of the sensitizer by passivating sub-band gap traps.