Negative Thermal Quenching via Thermally Activated Cross‐Relaxation in 3D‐Printed Fluorescent Silica Glass for High‐Temperature Thermometry

ABSTRACT Rare‐earth ion (RE 3 ⁺) doped glasses have been recognized for their chemical and thermal stability, making them promising for fluorescence‐based high‐temperature thermometry. However, processing silica glasses into the demanded geometries required by different sensing scenarios remains a tremendous challenge due to their high melting temperature and poor machinability and shapability. In this study, we present the fabrication of Tb 3 ⁺‐doped silica glass with complex structures using photopolymerization‐based 3D printing, which allows for the fabrication of intricate device architectures at reduced manufacturing temperatures (<1200 °C). Uniquely, Tb 3 ⁺ ions exhibit a heterogeneous distribution with the 3D‐printed glass, dominated by nanoscale Tb 3 ⁺‐enriched regions that facilitate temperature‐activated cross‐relaxation (CR). This unique distribution leads to a remarkable negative thermal quenching (NTQ) effect, with the overall fluorescence intensity increased by 138% from 298 to 868 K. The enhanced CR process promotes efficient energy transfer from the thermally unstable ⁵D 3 to the more stable ⁵D 4 level, thus modulating the emission spectra and improving quantum efficiency. The fabricated silica glass sensor demonstrates high optical quality, thermal and chemical stability, and rapid thermometric response—especially in high‐surface‐area honeycomb structures. Our results establish 3D printing as a transformative approach for developing robust, geometrically customizable optical sensors with unique photonic properties, enabling precise and reliable temperature sensing in harsh environments.