Mn²⁺/Mn⁴⁺co-doped LaM_1−xAl_11−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.