Self-reduction-induced BaMgP 2 O 7 :Eu 2+/3+ : a multi-stimuli-responsive phosphor for X-ray detection, anti-counterfeiting and optical thermometry.

Mixed-valence Eu 2+/3+ -activated phosphors have attracted wide attention due to their excellent luminescence tunability. Steady control of the Eu 2+ /Eu 3+ ratio is the key to achieving reproducible Eu 2+/3+ co-doped materials. In this work, BaMgP 2 O 7 : x Eu 2+/3+ (BMPO:Eu, x = 0.001-0.20) was successfully prepared by the traditional solid-state method in air. Eu 3+ undergoes selective self-reduction at Ba 2+ sites surrounded by a [P 2 O 7 ] framework, leading to quantitive Eu 2+ /Eu 3+ . The phosphors exhibit a blue-violet emission band at ∼410 nm due to 5d-4f transitions of Eu 2+ and a group of red emission peaks from 5 D 0 - 7 F J of Eu 3+ . Controllable multicolor emissions are realized by regulating the Eu content and excitations. A linear response of overall luminescence intensity to irradiation dose makes the phosphor appropriate for X-ray detection. The combination of UV-blue excitation-dependent color evolution and X-ray luminescence qualifies the phosphors with great potential for multi-level anti-counterfeiting. In addition, Eu 3+ presents abnormal anti-thermal quenching, so that the fluorescence intensity ratio (FIR) of Eu 2+ /Eu 3+ changes in the temperature range of 300-520 K, suggesting a promising application in optical thermometry. Therefore, selectively partial self-reduction in a multi-cationic host is an effective strategy to design mixed-valence co-doped materials, providing a multiplicity of applications.