Excellent temperature sensing characteristics of europium ions self-reduction Sr3P4O13 phosphors for ratiometric luminescence thermometer

Eu²⁺/Eu³⁺ co-doped Sr₃P₄O₁₃ phosphors were prepared by high temperature solid stated method in air atmosphere and studied in detail their luminescent properties in order to investigate the possible applications in temperature sensors. The broadband emission of Eu²⁺ ions and the linear emission band of Eu³⁺ ions can be observed in the photoluminescence (PL) spectra of Sr₃P₄O₁₃: Eu²⁺/Eu³⁺ phosphors due to the self-reduction effect. X-ray photoelectron spectroscopy (XPS), PL spectra, and time-resolved fluorescence lifetime confirm the formation of double emission centers of Eu²⁺ and Eu³⁺ ions in Sr₃P₄O₁₃ because of the self-reduction by charge compensation. In the Eu²⁺/Eu³⁺ co-activated Sr₃P₄O₁₃ thermometric phosphor, the blue emission of Eu²⁺ ions and red emission of Eu³⁺ ions, can be used as fluorescence intensity ratio (FIR) signals. In addition, the mechanism is discussed in detail based on the experimental data, and the strong temperature dependence is explained from the point of view of thermal quenching. Additionally, benefited from their diverse thermal quenching behavior, the FIR of Eu³⁺ to Eu²⁺ is fitted very well, and S_a reached a maximum 0.008 K⁻¹ at 573 K, while S_r reached a maximum of 1.06% K⁻¹ at 353K. As a consequence, this work indicates that Sr₃P₄O₁₃: Eu²⁺/Eu³⁺ phosphors could be widely applied in optical temperature sensors.