Dual green and red emission of novel Mn doped Mg0.3Zn0.7Al2O4 phosphors synthesized by a solid-state method for high-sensitivity temperature sensor applications.

Dual green and red-emitting Mn-doped Mg0.3Zn0.7Al2O4 (Mg0.3Zn0.7Al2O4:Mn) phosphors were successfully synthesized via a solid-state reaction method. Analyses using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), Raman, Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) confirm the successful substitution of Mn2+ for Mg2+/Zn2+ and Mn4+ for Al3+ in the [(Mg/Zn)O4] tetrahedral and [AlO6] octahedral sites within the Mg0.3Zn0.7Al2O4 lattice, respectively. The synthesized, high-purity Mg0.3Zn0.7Al2O4:Mn samples exhibit two characteristic emission bands centered at 510 nm and 678 nm, which are attributed to the 4T1 → 6A1 and 2E → 4A2 transitions of the Mn2+ and Mn4+ ions, respectively. The intensity ratio of the green to red emissions can be easily tuned by adjusting the doping concentration and excitation wavelength. The optimal emission intensities for the green and red bands were observed in the sample doped with 0.3% Mn and annealed at 1300 °C when excited at 426 nm and 314 nm, respectively. Under an excitation wavelength of 360 nm, the temperature-dependent emission spectra reveal distinct thermal quenching behaviors for Mn2+ and Mn4+ ions. The maximum absolute sensitivity (S a(FIR)) and relative sensitivity (S r(FIR)) based on the fluorescence intensity ratio (FIR) of Mn2+ and Mn4+ in Mg0.3Zn0.7Al2O4:0.3Mn were found to be 0.61 K-1 and S r = 1.59% K-1 at 483 K, respectively. Furthermore, this material exhibits excellent thermal stability, maintaining an FIR repeatability (R) of 99.8% at 463 K. These findings reveal that the synthesized novel Mg0.3Zn0.7Al2O4:Mn phosphor is a highly promising candidate for high-sensitivity optical thermometry.