<p>Lanthanide ion-doped Sc₂Mo₃O₁₂ upconversion (UC) luminescent materials exhibit a unique negative thermal quenching phenomenon, making them highly promising for applications in fluorescence thermometry. However, the luminescence intensity of Sc₂Mo₃O₁₂ phosphor is relatively low at room temperature, so it is urgently necessary to enhance the intensity of the phosphor at room temperature. In this study, Sc₂Mo₃O₁₂:Yb/Er/Al phosphors were synthesized via the solid-state reaction method, and the effects of Al³⁺ ion doping on their phase composition and upconversion fluorescence properties were investigated by X-ray diffraction (XRD) analysis and upconversion fluorescence spectra evaluation. The results show that the incorporation of Al³⁺ ions enhanced the UC intensity at room temperature and improved the fluorescence thermometry performance. The doping of Al³⁺ ions disrupts the lattice symmetry and reduces the distance between sensitizer ions (Yb³⁺) and activator ions (Er³⁺), increasing the UC intensity by approximately 4.2 times. In addition, the dependence of fluorescence properties of ScAl_0.6Mo₃O₁₂:18%Yb³⁺/2%Er³⁺ samples on temperature were tested, the negative thermal quenching effect was verified, and the thermal enhancement mechanism was explored. The maximum absolute and relative sensitivities of the ScAl_0.6Mo₃O₁₂:18%Yb³⁺/2%Er³⁺ reached 0.00635&#xa0;K⁻¹ at 372&#xa0;K and 0.00829%K⁻¹ at 300&#xa0;K, respectively, indicating the potential of the phosphor for applications in optical thermometry.</p>