A new optical temperature sensor based on the fluorescence intensity ratio of Mn²⁺ and Mn⁴⁺

In the course of preparing Mn-doped phosphors, the mix-valence state of Mn-n(+) ions may be obtained with associated interesting properties. This work prepared a new phosphor Ba3MgSb2O9:Mn (BMS:Mn) by a traditional high-temperature solid-state synthesis method. In this structure, Mn-n(+) can replace Mg2+ site as Mn2+ oxidation state or Sb5+ site as Mn4+. Moreover, the emitting bands of Mn2+ and Mn4+ at around 596 and 758 nm are simultaneously observed by using 350 nm as exciting wavelength. Interestingly, the temperature-dependent emitting intensities corresponding to Mn2+ and Mn4+ are different at temperatures from 10 to 300 K. With increasing temperature, the intensity of Mn2+ luminescence has some enhancement at 10-200 K and then decreases gradually, whereas Mn4+ luminescence goes into rapid decline. By using this character, BMS:0.01Mn can be used as an optical temperature sensor at 10-300 K based on the fluorescence intensity ratio of Mn2+ and Mn4+. The maximum relative sensitivity (S-r) at 125 K is as high as 1.51% K-1.