Tuning the emission color and temperature range of dual-mode luminescent thermometer by dopant valence states control

Abstract

Dual emitting materials are of great interest for luminescence thermometry. The operating temperature range, the thermal sensitivity as well as the emission color are crucial parameters, which define the competitiveness of the thermal sensor. In this work, we propose a new and convenient method for the modulation of emission color range and sensitivity through the control of the dopant oxidation states and crystal field variations. To this end, we investigated inorganic phosphors in which two valence states of Mn luminescent centers can be stabilized. When inserted in octahedral environment, Mn4+ ions present a red luminescence (2E → 4A2 transition), whereas Mn2+ ions exhibit a green luminescence in tetrahedral environment (4T1 → 6A1 transition). Due to the different behavior of Mn4+ and Mn2+ luminescence properties according to the temperature, the resulting emission color varies from red to green and can be exploited for visual temperature detection. We demonstrate the proportion of Mn4+ and Mn2+ ions can be finely tuned, owing to a thermally driven Mn4+ to Mn2+ reduction, which allows to modulate color change at a specific temperature. Two isostructural materials were investigated, SrMgAl10O17:Mn4+,Mn2+ and BaMgAl10O17:Mn4+,Mn2+, and can be envisioned as competitive ratiometric and colorimetric luminescent thermometer, with tunable properties.