Editors: | F. Kongoli, F. Marquis, S. Kalogirou, B. Raveau, A. Tressaud, H. Kageyama, A. Varez, R. Martins. |
Publisher: | Flogen Star OUTREACH |
Publication Year: | 2022 |
Pages: | 154 pages |
ISBN: | 978-1-989820-34-6 (CD) |
ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
Summary γ-Al-2O3:Sm2+ coatings were synthesized by the plasma electrolytic oxidation (PEO). The emissions originate from 4f55d1→4f6 and 4f6→4f6 transitions of Sm2+. The emission spectra, recorded from 300 K to 673 K, reveled the rapid diminution of the 5D0→7FJ transitions with increasing temperature. The 5d→4f broad-band emission increases in intensity up to 225 °C. The high-luminescence intensities and opposite intensity vs temperature trends of these emissions are an indication of the high sensitivities and low temperature resolution. The luminescence intensity ratio (LIR) are well-fitted to the Boltzmann distribution and the energy-crossover model with relative sensitivities: 3.5 %K-1 @ 300 K and 1.5 %K-1 @ 540 K. Introduction Sm2+ has a wide excitation band [1]. The emission spectrum of Sm2+ features a broad-band due to 5d-4f transition and a series of sharp peaks due to 4f-4f transitions. The discovery of Al2O3:Sm2+ [1] provided an opportunity for the investigation of this material as temperature sensor. The indications of its high potential for the phosphor thermometry were the existence of both the 5d-4f and 4f-4f emissions, high emission intensities, wide choice of excitation wavelengths, and the sole importance of the substrate material itself. The significant overlap of 5d with 5D0 level is an indication of the highly efficient f-f transitions [2]. The complete thermometric analysis was carried out. Methods 99.9% pure aluminium, 6061 and 7075 aluminium alloys were used as anode during the PEO. XRD was used for investigation of the coating crystallinity. High-stability 473 nm laser was used as an excitation source. The beams were transferred via a fiber-optic bundle. Emission spectra were recorded by the high-resolution spectrograph. The samples were placed on the liquid nitrogen cooled hot/cold stage. Results Emission spectra for LIR and LT were recorded from 100 K to 673 K. The 5D0→7FJ emissions rapidly drop with increasing temperature, while the 4f-5d increases up to 225 °C. LIR is estimated from the ratio of 5d-4f and 4f-4f transitions, giving the excellent relative sensitivity values. Luminescence lifetime of 5D0→7F0 is fitted to the energy crossover model [3], with maximum relative sensitivity 1.5 %K-1 @ 540 K. Conclusions A steady-state and time-resolved thermometry on a wide temperature range was carried out on the highly luminescent phosphor incorporated in the coatings of possibly the most important industrial material. LIR following Boltzmann distribution showed sensitivity among the highest ever recorded. The lifetime rapidly drops with increasing temperature.
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