Highly-increased photoluminescence of Pr3+ due to the Eu2+→ Pr3+ energy transfer in Al2O3 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 H-3(4) into higher levels P-3(J) (J = 0, 1, 2), while PL emission spectra contain several bands attributed to transitions of Pr3+ from excited levels P-3(0) and P-3(1) to the lower multiplets( 3)H(J) (J = 4, 5, 6) and F-3(J) (J = 2, 3, 4). Among these transitions, P-3(0)-> F-3(2) transition in the red region (644 nm) is the most intense. PL emission intensity of Pr3+ increases by co-doping Eu2+ into Al2O3:Pr(3+ )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, P-3(0)-> F-3(2) 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 Al(2)O(3 )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.