Luminescence of Ti-Sapphire coatings prepared by plasma electrolytic oxidation and their application in temperature sensing

15 mu m thick Ti-Sapphire coatings were synthesised at room temperature by the plasma electrolytic oxidation (PEO) method for 20 min from the pure aluminium substrate and with the addition of the TiO2 particles in various concentrations in the supporting electrolyte. The coatings are featured by microscopic pores typical for PEO surfaces. The dominant is the alpha phase of alumina with the small presence of the gamma phase. The estimated average crystalline size is 41 nm. Ti is uniformly distributed in these polycrystalline ceramic coatings and does not affect morphology or phase content. Photoluminescence of PEO-created coatings shows typical absorption, excitation, and emission features of Ti-Sapphire with two broad-overlapping excitation bands in the green and blue spectral region due to the Jahn-Teller splitting of the E-2(g) level and the Stokes shifted emission centred at 720 nm. E-2(g) energy state splitting is equal to 2195 cm(-1) and 10 Dq approximate to 19,300 cm(-1). The highest emission intensity was observed in the coating prepared with the 0.1 g/L TiO2 powder concentration, i.e. 0.32 at% of incorporated Ti3+. Emission spectra recorded at temperatures ranging from 100 K to 300 K revealed the Mott-Seitz temperature dependence of emission intensity with the 1180 cm(-1) activation energy. The fit to the McCumber-Sturge relation gave, for the first time, the value of Debye temperature of 594 K of Al2O3:Ti. Non-contact, luminescence temperature sensing from the temperature-induced changes in the emission bandwidth gave a high sensitivity of 3.2 cm(-1) K-1 and 0.19 K temperature resolution. The PEO created Ti-sapphire coatings are a promising multifunctional barrier level - optical temperature sensor material for applications in harsh environments or on large aluminium surfaces. It shows potential to be used as a planar waveguide Ti-Sapphire laser active medium. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

15 mu m thick Ti-Sapphire coatings were successfully synthesized using plasma electrolytic oxidation (PEO) method on pure aluminum substrates with the addition of TiO2 particles. The coatings exhibit typical Ti-Sapphire photoluminescence features and show potential as multifunctional barrier-level optical temperature sensor materials.