Tunable white-light emission and energy transfer in single-phase Bi3+, Eu3+ co-doped Ba9Y2Si6O24 phosphors for UV w-LEDs

In this paper, a series of Bi3+ and Eu3+ single-doped as well as Be3+, Eu3+ co-doped Ba9Y2Si6O24 samples were synthesized through a simple high-temperature solid- state reaction method. Their crystal structures, morphologies, luminescent properties, temperature-dependent emission spectra, decay curves and quantum efficiencies were investigated in detail. Upon ultraviolet light excitation, Bi3+ single-doped samples exhibited blue and green emissions peaking at 408 and 501 nm, corresponding to the P-3(1)-S-1(0), transition of Be3+ ions. The spectral analysis indicated that there were two different luminescent centers of Bi3+ ions due to different occupancies in Ba9Y2Si6O24 host lattice. And the highest quantum efficiency can reach 64.5% in Ba9Y2Si6O24:0.024Bi(3+) phosphor. The remarkable spectral overlap between the emission spectra of Bi3+ ions and the excitation spectra of Eu3+ ions indicated the exist of energy transfer from Bi3+ to Eu3+. The efficient energy transfer from Bi3+ to Eu3+ has been investigated in detail and resulted in that tunable and white-light emission can be obtained by modulating Eu3+ doping concentration. White emission can be realized with the CIE coordinates of (0.357, 0.345) and quantum efficiency of 57.6% for Ba9Y2Si6O24:0.024Bi(3+),0.02Eu(3+). The above results demonstrate that Ba9Y2Si6O24:Bi3+, Eu3+ may be a potential candidate for ultraviolet (UV) driven white light-emitting diodes (w-LEDs).