Rare earth nanoparticles: Illuminating the future of precision photodynamic therapy in oncology

Rare earth nanoparticles (RENPs) have emerged as promising nanoplatforms for photodynamic therapy (PDT) owing to their optical conversion capability, tunable emission, imaging compatibility, and surface-engineering flexibility. RENPs can convert deeply penetrating near-infrared (NIR) light or high-energy radiation into emissions that activate photosensitizers (PSs), thereby improving light delivery, reactive oxygen species (ROS) generation, and spatiotemporal therapeutic control. This review summarizes recent advances in RENP-mediated PDT, focusing on photosensitizer activation, tumor targeting, regulated cell death, and ROS amplification. We also discuss RENP-based theranostic and multimodal therapeutic platforms that combine imaging guidance with photothermal therapy (PTT), chemotherapy, immunotherapy, gene regulation, and tumor microenvironment (TME) modulation. Finally, we critically analyze the major translational barriers, including limited optical conversion efficiency under clinically acceptable power densities, excitation-induced heating, tumor hypoxia, antioxidant defense, scalable manufacturing, long-term biosafety, and patient stratification. Future development should prioritize simplified material design, standardized quality control, low-power excitation, reliable safety evaluation, and indication-specific clinical positioning.