Sensitizing effect of Ce³⁺ on Tm³⁺ blue emission in Al<inf>2</inf>O<inf>3</inf>:Tm³⁺/Ce³⁺ coatings formed by plasma electrolytic oxidation

Abstract

This paper is devoted to the study of the photoluminescent (PL) characteristics of blue-emitting Al2O3:Tm3+ and Al2O3:Tm3+/Ce3+ coatings. The presented coatings were synthesized by plasma electrolytic oxidation process of aluminum in electrolyte containing Tm2O3 and Tm2O3/CeO2 particles, and characterized by SEM/EDS, XRD, and PL emission and excitation spectra. Al2O3:Tm3+ coatings show a blue emission with maximum at 455 nm, originated from the 1D2→3F4 transition of Tm3+, under 361 nm excitation (3H6→1D2 transition of Tm3+). Intensity of 1D2→3F4 transition boosts by co-doping Ce3+ into Al2O3:Tm3+ coatings due to energy transfer from Ce3+ to Tm3+, occurring because of the overlap between PL emission spectrum of Ce3+ excited by middle ultraviolet radiation and PL excitation spectrum of Tm3+ in Al2O3 host. Under middle ultraviolet excitation, Al2O3:Tm3+/Ce3+ coatings display two intense PL emission bands attributed to the characteristic electric dipole 4f–5d transition of Ce3+ (at 330 nm) and 1D2→3F4 transition of Tm3+ (at 455 nm). Blue PL emission of Tm3+ in Al2O3:Tm3+/Ce3+ coatings is one to two order of magnitude larger than in Al2O3:Tm3+ coatings.