Europium Ions Self‐Reduction Benefiting from AlO 4 /Si(Al)O 4 Network Structure for Multimode Optical Thermometry Manometry

Mixed‐valence europium ions‐activated phosphors have distinct advantages in color modulation, dynamic anti‐counterfeiting, and optical sensors. Nevertheless, it is still a challenge to obtain mixed‐valence europium ions in single compounds by facile self‐reduction. Herein, the crystal structure of a 3D hexagonal network formed by SiO 4 /AlO 4 tetrahedra is demonstrated to play a significant role in the spontaneous reduction of Eu 3+ to Eu 2+ based on SrAl 2 Si 2 O 8 , Sr 2 SiO 4 , SrAl 2 O 4 hosts. The crystal field theory and Judd‐Ofelt theory provide a deeper understanding of Eu 2+ and Eu 3+ luminescence behavior, namely, the low energy spectra of Eu 2+ are more easily observed in crystal structure with high polarizability and octahedral coordination, whereas the spectra properties of Eu 3+ are affected by the symmetry of local environment and crystal rigidity. For SrAl 2 Si 2 O 8 : 0.02Eu 2+ /Eu 3+ , multi‐mode thermometry is explored in terms of the luminescence intensity ratio (LIR) of Eu 2+ /Eu 3+ , luminescence intensity (LI) and full‐width at half maximum (FWHM) of Eu 2+ with maximal relative sensitivity reaching 3.83% K −1 . This study presents the first exploration of optical manometry based on the LIR mode of Eu 2+ /Eu 3+ with excellent sensitivity ( S r = 18.13% GPa −1 ). This work not only provides a novel strategy for the design of mixed‐valence ions‐activated materials but also constructs promising optical thermometry, and manometry candidates.