Highly-increased photoluminescence of Pr³⁺ due to the Eu²⁺→ Pr³⁺ energy transfer in Al<inf>2</inf>O<inf>3</inf> coatings formed by plasma electrolytic oxidation

Abstract

In this paper, photoluminescence (PL) properties of Pr3+ single doped and Pr3+/Eu2+ co-doped Al2O3 coatings formed by plasma electrolytic oxidation of aluminum were investigated. The PL spectra of Al2O3:Pr3+ coatings feature bands ascribed to 4f-4f transitions of Pr3+. PL excitation spectra contain three broad bands in the violet and blue regions which correspond to the direct excitation of the Pr3+ ground state 3H4 into higher levels 3PJ (J = 0, 1, 2), while PL emission spectra contain several bands attributed to transitions of Pr3+ from excited levels 3P0 and 3P1 to the lower multiplets 3HJ (J = 4, 5, 6) and 3FJ (J = 2, 3, 4). Among these transitions, 3P0→3F2 transition in the red region (644 nm) is the most intense. PL emission intensity of Pr3+ increases by co-doping Eu2+ into Al2O3:Pr3+ coatings due to the energy transfer from Eu2+ to Pr3+, occurring due to the overlap between PL emission spectra of Eu2+, excited by middle ultraviolet radiation, and PL excitation spectra of Pr3+ in Al2O3 host. Under middle ultraviolet excitation, 3P0→3F2 transition of Pr3+ in Al2O3:Pr3+/Eu2+ coatings is 62 times more intense than without co-doping and 16 times if comparison is made with Al2O3:Pr3+ excited by 446 nm. The total luminescence intensity of Al2O3 co-doped with Pr3+/Eu2+ and doped with Pr3+ is 3.6 times more intense of the former if both samples are excited by 446 nm. The gains are linearly increasing with Eu2+ doping concentration. Al2O3:Pr3+/Eu2+ poses as an alternative phosphor to YAG:Ce3+ for the creation of neutral white LEDs by excitation with InGaN semiconductors.