Controlling lanthanide-doped upconversion nanoparticles for brighter luminescence

This review focuses on the enhancement of upconversion luminescence from lanthanide-doped nanoparticles. The unique luminescence capability of long-wavelength absorption and then efficient short-wavelength radiation makes these nanoparticles have attractive potential in numerous photonic and biophotonic fields. However, the dark luminescence limited by the low upconversion quantum yield hinders their applications in in vivo and in photovoltaics. In this work, we first present the fundamental concepts of upconversion luminescence based on energy transfer upconversion, which is the most widespread and the efficient upconversion process. Subsequently, we present the varying strategies to enhance upconversion luminescence intensity from the excitation, energy transfer, and radiation perspectives. (topical review)