Supersensitive Sm²⁺-Activated Al<inf>2</inf>O<inf>3</inf> Thermometric Coatings for High-Resolution Multiple Temperature Read-Outs from Luminescence

Abstract

The introduction of additional functionalities to materials is exceptionally important as it opens new applications for them. Aluminum, one of the most abundant and important materials, is coated with luminescent Sm2+-doped γ-aluminium oxide to impart thermometric functionality. Considering the potential industrial applications, two of the most widely used aluminum alloys, 6061 and 7075, are also coated. For this purpose, plasma electrolytic oxidation (PEO), an effective technique for producing hard ceramic coatings on various metal surfaces, is used. It is shown that thermometric coatings can be produced on aluminum in one-step process by adding the raw precursor to the electrolyte. The valence reduction of Ln3+ to Ln2+ is achieved during the PEO process. The intense and broad (orange to deep red) emission from the coating shows supersensitivity to temperature changes over the 100–648 K range. The temperature is obtained from the coating emission using i) the emission intensity ratio method, ii) emission lifetime, and iii) emission band position with sensitivities of 4.8% K−1, 1.2% K−1, and 8 cm−1 K−1, respectively. Several applications would benefit from the thermometric coating's excellent temperature resolution of 0.04 K and the choice of three temperature read-outs that facilitate the coating's use in different luminescence thermometry setups.