Mn2+/Mn4+co-doped LaM1−xAl11−yO19(M = Mg, Zn) luminescent materials: electronic structure, energy transfer and optical thermometric properties

Dual-emitting manganese ion doped LaM_1-xAl_11-yO₁₉ (M = Mg, Zn) phosphors were prepared by substituting Zn²⁺/Mg²⁺ with Mn²⁺ and replacing Al³⁺ with Mn⁴⁺. The LaM_1-xAl_11-yO₁₉:xMn²⁺,yMn⁴⁺ phosphors show a narrow green emission band of the Mn²⁺ ions at 514 nm and a red emission band of the Mn⁴⁺ ions at 677 nm. In addition, the thermal stability of luminescence shows that the response of Mn²⁺ and Mn⁴⁺ to the temperature is obviously different in LaMAl₁₁O₁₉, implying the potential of the prepared phosphors as optical thermometers. The decay lifetime of Mn⁴⁺ was changed with temperature due to the different fluorescence intensity ratios of Mn²⁺ and Mn⁴⁺, and a dual-mode optical temperature-sensing mechanism was studied in the temperature range of -50-200 °C. The maximum relative sensitivities (S_r) are calculated as 3.22 and 3.13% K^-1, respectively. The unique optical thermometric features demonstrate the application potential of LaMAl₁₁O₁₉:Mn²⁺,Mn⁴⁺ in optical thermometry.