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Dual-emitting and thermochromic manganese ion single doped ZnGa 2−y Al y O 4 phosphors were prepared by solid-state reaction. The regulation of the valence state and the luminescent properties, especially the luminescent thermal stability of manganese ions in ZnGa 2−y Al y O 4 , are discussed in detail. When excited by ultraviolet (UV) light, the emission spectra of ZnGa 2 O 4 :Mn 2+ ,Mn 4+ present an ultranarrow green emission band at 503 nm with a fwhm of 22 nm, which derives from the Mn 2+ ions formed by the self-reduction of doped Mn 4+ , and a red emission band of the Mn 4+ ions at 669 nm. In addition, a ZnGa 2−y Al y O 4 :Mn 2+ ,Mn 4+ solid solution was designed and synthesized by Al 3+ replacing Ga 3+ . The doping of Al 3+ effectively inhibited the degree of Mn 4+ self-reduction to Mn 2+ , thus realizing the regulation of valence state of manganese ions. Interestingly, the thermal stability of luminescence shows that the response of Mn 2+ and Mn 4+ to temperature is obviously different in ZnGa 2−y Al y O 4 , implying the potential of the prepared phosphors as optical thermometers. Subsequently, three kinds of optical thermometers with superior color discrimination and high relative sensitivity (S r ) based on the fluorescence intensity ratio (FIR) technique were realized in 100−475 K. The S r value of ZGO:0.005Mn/ZGA 0.5 O:0.005Mn/ZGAO:0.005Mn phosphors can be as high as 4.345%/4.001%/3.488% K −1 (at 350/325/400 K), reflecting the great potential of ZnGa 2 O 4 :Mn 2+ ,Mn 4+ for optical thermometry applications.

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