Energy‐Relay‐Engineered Upconversion Emission with Intrinsic Environmental Responsiveness

Abstract

ABSTRACT Lanthanide‐based upconversion nanoparticles (UCNPs) offer excellent photostability and large anti‐Stokes shifts but are often limited by poor environmental responsiveness, hindering sensing applications. To address this challenge, we developed an energy‐relay strategy by integrating near‐infrared (NIR) dyes with Er 3+ /Tm 3+ doped UCNPs. Under 980 nm excitation, Yb 3+ transfers energy to Tm 3+ and Er 3+ , excited Tm 3+ ions then pass their energy to NIR dyes such as Cy7.5, which subsequently relay it back to Yb 3+ ions, enabling a second Yb 3+ ‐to‐Er 3+ energy transfer. This cascade process amplifies Er 3+ emission while quenching Tm 3 + emission. In Cy7.5‐modified Er 3+ /Tm 3+ doped UCNPs (NaYbF 4 :Er@NaYbF 4 @NaYbF 4 :Tm@NaYbF 4 @NaLuF 4 ), the energy‐relay effect enhances the Er 3+ /Tm 3+ ratiometric signal by two orders of magnitude. The process is highly dependent on the dopant architecture, as swapping Er 3+ and Tm 3+ positions disrupts the relay. The generality of this strategy is supported by similar energy‐relay observed with Cy7 and IR806. Despite the incorporation of dyes, our energy‐relay design retains the excellent photostability characteristic of lanthanide upconversion while introducing environmental responsiveness. As a proof of concept, the energy‐relay nanoprobe demonstrated high sensitivity in both thermal and chemical sensing. Our findings establish energy‐relay engineering as a versatile design principle for designing stable, efficient, and responsive upconversion nanoprobe platforms.