Engineering Ho3+-Mediated Energy Transfer for Enhanced Pr3+ NIR-II Luminescence in Core–Shell Nanocrystals toward Ultrasensitive Temperature Sensing

Near-infrared II (NIR-II, 1000–1700 nm) luminescence has emerged as a powerful tool for biomedical applications, including sensing, imaging, and drug delivery, owing to its superior tissue penetration depth and high spatial resolution. Lanthanide-based NIR-II nanoprobes are particularly promising due to their outstanding photostability and minimal cytotoxicity. However, two critical challenges impede their widespread implementation: severe thermal quenching at elevated temperatures and inefficient downshifting processes. Herein, a novel strategy is reported to address these limitations by precisely modulating energy transfer dynamics between Ho 3+ and Pr 3+ ions in NaYF 4 core–shell engineering. By carefully optimizing the concentration ratio and spatial distribution of these lanthanide ions in NaYF 4 core–shell nanocrystals, the population of 1 G 4 (Pr 3+ ) is significantly increased, effectively suppressing thermal quenching while boosting downshifting efficiency. The optimized system leverages dual NIR-II emission channels ( 1 G 4 and 5 I 6 ) in NaYF 4 :Yb 3+ /Ho 3+ @NaYF 4 :Yb 3+ /Pr 3+ nanocrystals, enabling ultrasensitive temperature sensing with a maximum relative sensitivity ( S r ) of 2.03% K −1 . Furthermore, the synergistic up/down-conversion properties of Ho 3+ and Pr 3+ facilitate multimodal anti-counterfeiting, offering a robust platform for advanced information encryption and storage. This work not only establishes a new paradigm for engineering NIR-II luminescence but also underscores their vast potential in advanced applications, from precision biosensing to high-security encoding technologies.