From quencher to potent activator – Multimodal luminescence thermometry with Fe3+ in the oxides MAl4O7 (M = Ca, Sr, Ba)

Luminescence (nano)thermometry is an emerging and promising field for remote temperature sensingand thermal imaging of both the surface and interior of objects. While the field is dominated by trivalentlanthanide ions (Ln3+) the transition metal ions have a so far underestimated role in that regard, althoughtheir luminescence properties are far more sensitive to changes in the embedding host matrix than inthe case of the Ln3+ions. In this work, we demonstrate the potential of the abundant Fe3+ion as acandidate for sensitive luminescence thermometry in the aluminate hosts MAl4O7(M = Ca, Sr, Ba).Although this ion is usually considered an efficient luminescence quencher, it is shown that a targetedcontrol of its luminescence properties makes this activator an interesting and only scarcely investigatedalternative to the Ln3+ions. We investigated the possibility for different modes of luminescencethermometry with Fe3+(eventually co-doped with Tb3+as internal thermally insensitive intensityreference), which include absolute intensity, ratiometric or lifetime thermometry. By selective changes inthe Fe–O bond distances, it is possible to modulate the relative sensitivity towards values as high asaround 2% K1at room temperature in CaAl4O7:Fe3+,Tb3+and connected relative temperature uncer-tainties of around 0.3%.