Near Infrared Light Sensitive Ultraviolet–Blue Nanophotoswitch for Imaging-Guided “Off–On” Therapy

Photoswitchable materials are important in broad applications. Recently appeared inorganic photoswitchable upconversion nanoparticles (PUCNPs) become a competitive candidate to surmount the widespread issue of the organic counterparts —photobleaching. However, current PUCNPs follow solely Yb3+/Nd3+ cosensitizing mode, which results in complex multilayer doping patterns and imperfectness of switching in UV–blue region. In this work, we have adopted a new strategy to construct Nd3+ free PUCNPs—NaErF4@NaYF4@NaYbF4:0.5%Tm@NaYF4. These PUCNPs demonstrate the superior property of photoswitching. A prominent UV–blue emission from Tm3+ is turned on upon 980 nm excitation, which can be completely turned off by 800 nm light. The quasi-monochromatic red upconversion emission upon 800 nm excitation—a distinct feature of undoping NaErF4 upconversion system—endows the PUCNPs with promising image-guided photoinduced “off–on” therapy in biomedicine. As a proof-of-concept we have demonstrated the imaging-guided photodynam...