Novel Ba3Lu4O9:Bi3+,Eu3+ phosphors for white LEDs: Efficient energy transfer, broad near-UV excitation band and green-yellow-orange-red color tunable emissions

Abstract

In this work, we reported novel single-component color-tunable Ba3Lu4O9:Bi3+,Eu3+ phosphors for near-ultraviolet (near-UV) pumped white light-emitting diodes. A series of Ba3Lu4O9:1%Bi3+,xEu3+ (x = 0, 2%, 4%, 6%, 8%, 10%, 15% and 25%) have been successfully synthesized via a conventional high-temperature solid-state reaction method. Rietveld refinement method revealed that the as-prepared Ba3Lu4O9:Bi3+,Eu3+ samples had the trigonal structure with the space group R3. The Ba3Lu4O9:1%Bi3+,xEu3+ phosphors possessed a broad excitation band in the near-UV range of 240–400 nm with a maximum at 356 nm. Upon excitation at 356 nm, the emission spectra of the Ba3Lu4O9:1%Bi3+,xEu3+ phosphors included a broad emission band in the 400–750 nm peaking at 551 nm and many sharp characteristic emission lines centered at 539, 582, 595, 614, 656, 705 nm, which were originated from the allowed 3P1→1S0 transition of the Bi3+ ion, the 5D1→7F1 and the 5D0→7FJ (J = 0, 1, 2, 3, 4) transitions of the Eu3+ ion, respectively. The energy transfer phenomenon from Bi3+ to Eu3+ ions was observed from Ba3Lu4O9:1%Bi3+,xEu3+ phosphors under the excitation of 356 nm, and the Bi3+→Eu3+ energy transfer mechanism was determined to be a resonant type via quadrupole-quadrupole interaction. Due to the efficient Bi3+→Eu3+ energy transfer, the green-yellow-orange-red color tunable emissions were realized in Ba3Lu4O9:1%Bi3+,xEu3+ phosphors by increasing the Eu3+ doping concentration.