Dual green and red emission of novel Mn doped Mg_0.3Zn_0.7Al₂O₄ phosphors synthesized by a solid-state method for...

Dual green and red-emitting Mn-doped Mg_0.3Zn_0.7Al₂O₄ (Mg_0.3Zn_0.7Al₂O₄: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 Mg_0.3Zn_0.7Al₂O₄ lattice, respectively. The synthesized, high-purity Mg_0.3Zn_0.7Al₂O₄: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 Mg_0.3Zn_0.7Al₂O₄:0.3Mn 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 Mg_0.3Zn_0.7Al₂O₄:Mn phosphor is a highly promising candidate for high-sensitivity optical thermometry.