Six-photon upconverted excitation energy lock-in for ultraviolet-C enhancement

Abstract Photon upconversion of near-infrared (NIR) irradiation into ultraviolet-C (UVC) emission offers many exciting opportunities for drug release in deep tissues, photodynamic therapy, solid-state lasing, energy storage, and photocatalysis. However, NIR-to-UVC remains a daunting challenge due to low quantum efficiency. Here, we report an unusual six-photon process Gd 3+ /Tm -codoped nanoparticles following heterogeneous core-multishell architecture. This design efficiently suppresses consumption induced by interior traps, maximizes cascade sensitizations the NIR excitation, promotes upconverted UVC from high-lying excited states. We realized intense six-photon-upconverted UV emissions at 253 nm under 808 excitation. work provides insight mechanistic understanding within architecture, while offering developing nanoscale emitters that can be remotely controlled through tissues upon illumination.