Photoluminescence properties and local electronic structures of rare earth-activated Sr₃AlO₄F

Photoluminescence properties and local electronic structures of rare earth (Eu³⁺ and Ce³⁺) activated Sr₃AlO₄F have been studied. X-ray powder diffraction data indicated that the activator ions of Eu³⁺ and Ce³⁺ can be incorporated into the Sr₃AlO₄F lattice and formed limited solid solutions of Sr_3-2xLn_xNa_xAlO₄F (Ln = Eu, Ce) with Na⁺ as a charge compensator ion. The local structure around Sr sites was initially explored using Eu-activated Sr₃AlO₄F as a structural probe. Sr₃AlO₄F:Eu³⁺ exhibits orange-red emission ranging from 520 to 740 nm with a maximum peak at about 619 nm mainly originating from the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions, indicating that Eu exists mainly in the trivalent state due to a strong oxidative lattice in Sr₃AlO₄F. Sr₃AlO₄F:Ce³⁺ shows an unusual long-wavelength 4f → 5d excitation band of Ce³⁺ at about 405 nm due to a large crystal field splitting of the 5d levels of Ce³⁺ in relation to its crystal structure. Under near-UV excitation in the range of 375-405 nm, Sr₃AlO₄F:Ce³⁺ exhibits efficient blue-green emission at about 506 nm. Given high absorption and efficient excitation in the near-UV region, Sr₃AlO₄F:Ce³⁺ demonstrates a potential blue-green emitting phosphor for applications in white LED lighting.