Abstract
Plasma electrolytic oxidation (PEO) of aluminum in electrolytes containing CeO2 and Eu2O3 powders in various concentrations was used for creating Al2O3 coatings doped with Ce3+ and Eu2+ ions. Phase and chemical composition, surface morphology, photoluminescence (PL) properties and energy transfer from Ce3+ to Eu2+ were investigated. When excited by middle ultraviolet radiation, Al2O3:Ce3+/Eu2+ coatings exhibited intense and broad emission PL bands in the ultraviolet/visible spectral range, attributed to the characteristic electric dipole 4f05d1→4f1 transition of Ce3+ (centered at about 345 nm) and 4f65d1→4f7 transition of Eu2+ (centered at about 405 and 500 nm). Due to the overlap between the PL emission of Al2O3:Ce3+ and the PL excitation of Al2O3:Eu2+, energy transfer from Ce3+ sensitizer to the Eu2+ activator occurs. The energy transfer is identified as an electric dipole–dipole interaction. The critical distance between Eu2+ and Ce3+ ions in Al2O3 was estimated to be 8.6 Å by the spectral overlap method.
Highlights
Ce3+ and Eu2+ ions have found widespread use as activators in luminescent materials because their parity allows 4f1 →4f0 5d1 and 4f7 →4f6 5d1 electric dipole transitions, respectively
During the Plasma electrolytic oxidation (PEO) of aluminum, Al2 O3 layer grows at the oxide/electrolyte and aluminum/oxide interfaces as a consequence of a strong electric field (~107 V/cm) induced relocation of O2− /OH− and Al3+ ions across the oxide [15]
Local temperature at the micro-discharge sites is higher than the melting points of CeO2 and Eu2 O3 particles (~2400 ◦ C), enabling the molten particles to react with Al2 O3 and form Ce and Eu ions doped Al2 O3 coatings
Summary
Ce3+ and Eu2+ ions have found widespread use as activators in luminescent materials because their parity allows 4f1 →4f0 5d1 and 4f7 →4f6 5d1 electric dipole transitions, respectively. Outer orbitals at 5d states of Ce3+ and Eu2+ ions are sensitive to crystal-field splitting and nephelauxetic effects [1,2], energy positions of excitation and emission bands of these ions can be tuned by changing the host matrix. Ce3+ ion acts as an effective sensitizer due to its effective absorption [3]. Numerous studies demonstrated the importance and methods for enhancing the photoluminescence (PL) via an efficient energy transfer (e.g., [4,5]). The energy transfer from the Ce3+ sensitizer to the Eu2+ activator has been reported for some Ce3+ /Eu2+ doped host lattices because of the spectral overlap between Ce3+. The aim of this work is to investigate PL properties of
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