Excitation pathway and temperature dependent luminescence in color tunable Ba5Gd8Zn4O21:Eu3+ phosphors

A series of polycrystalline Ba5Gd8Zn4O21:Eu3+ phosphors were synthesized by a solid state reaction for the first time. The crystal structures were examined by means of X-ray diffraction. The luminescence spectra and decay curves were investigated as a function of Eu3+ concentration and temperature. It was found that the luminescent color of phosphor can be adjusted from white to red with the increase of Eu3+ concentration. Interestingly, emission spectra with different D-5(0)/D-5(1,2,3) ratios were observed when excited at 276 (corresponding to the O2- -> Eu3+ charge transfer band) and 395 nm (f-f transition F-7(0) -> L-5(6)). The energy transfers between Eu3+ ions in Ba5Gd8Zn4O21 have been confirmed to be resonant type via exchange interaction for the D-5(0) level and electric dipole-dipole interaction for D-5(J) (J = 1-3) levels. Temperature dependent measurements revealed that the crossover process is the main mechanism for quenching luminescence of the D-5(0) level of Eu3+ in the Ba5Gd8Zn4O21:Eu3+ phosphors. Finally, Judd-Ofelt parameters of Eu3+ in the Ba5Gd8Zn4O21 phosphors were calculated by a facile method in the framework of the J-O theory, in which the refractive index of Ba5Gd8Zn4O21 was deduced to be about 1.95.