Bandshift Luminescence Thermometry Using Mn4+:Na4Mg(WO4)3 Phosphors

The feasibility of employing Mn4+-activated phosphors for bandshift ltiminesence thermometry is demonstrated for the first time using Mn4+:Na4Mg(WO4)(3). Substitution of Mn4+ for Mg2+ in Na4Mg(WO4)(3) yields phosphors in which Mn4+ activators are distributed over (Na/Mg)(2)O-10 dimers. Neutron powder diffraction reveals that metal-oxygen bond distances in these dimers are significantly longer than those typically observed in Mn4+-activated phosphors. Multisite distribution of Mn4+ activators coupled to long metal-oxygen distances impart thermometric functionality to Mn4+:Na4Mg(WO4)(3). Red emission from two distinct Mn4+ emitters leads to a broad band extending from 560 to 850 nm. Differential thermal quenching of these emitters drives a sigmoidal blueshift of the emission maximum upon increasing temperature from 100 to 400 K (ca. 30 nm); bandshift luminescence thermometry is thus realized. Quantitative assessment of the thermometric performance of Na4Mg0.940Mn0.030(WO4)(3) yields a sensitivity of 0.127 nm K-1, a repeatability greater than 99%, and a temperature resolution, of 2.5 K at 300 K. Findings presented in this article expand the scope of applicability of Mn4+-activated thermosensitive phosphors beyond ratiometric bandshape and lifetime thermometry. More importantly from the perspective of developing new phosphors, our results provide structural guidelines for discovering and screening novel oxide hosts for Mn4+ activators.