ZnGaAlO:Mn,Mn Thermochromic Phosphors: Valence State Control and Optical Temperature Sensing.

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