Superelastic Subcrystalline Rare‐Earth Ceramic Nanofiber Aerogels Enable 1300°C‐Stable Upconversion Luminescence

Abstract

ABSTRACT Real‐time noncontact temperature detection is critical for the reliable operation of specialized robots in extreme thermodynamic environments. Upconversion (UC) luminescent materials, owing to their temperature‐sensitive emission, offer a promising solution. However, traditional UC crystals are fundamentally limited by both severe thermal quenching above 250°C and intrinsic brittleness. Here, we break these barriers by developing a subcrystalline upconversion ceramic nanofiber aerogel through an interfacial phonon engineering strategy. Our approach embeds active rare‐earth nanocrystals within an amorphous alumina matrix, creating a tensile‐strained heterointerface that softens local phonon modes and efficiently scatters high‐frequency vibrations. This unique “phonon cage” architecture suppresses nonradiative decay pathways, enabling stable UC emission at the unprecedented temperature of 1300°C. Furthermore, the subcrystalline structure induces a higher‐order sinusoidal buckling behavior, endowing the aerogel with thermomechanical superelasticity. The aerogel fully recovers from 95% compressive strain and survives over 1000 fatigue cycles, retaining >80% of its elasticity after 100 rigorous compression cycles under 1300°C thermal load. This work paves the way for noncontact thermal sensing in extreme environments.