Engineering Ho ³⁺ ‐Mediated Energy Transfer for Enhanced Pr ³⁺ NIR‐II Luminescence in Core–Shell Nanocrystals toward Ultrasensitive Temperature Sensing

Abstract 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.