Eu2+-Doped NaBa4(AlB4O9)2X3 (X = Cl, Br) phosphors with intense two-center blue emission and high color purity for n-UV pumped white light-emitting diodes

Highly efficient blue-emitting NaBa4(AlB4O9)(2)X-3 (X = Cl, Br): Eu2+ phosphors (NBAC: Eu2+ and NBAB: Eu2+) were prepared by solid-state reaction. Two different crystallographic cation sites of Eu2+ ion occupancy were confirmed by Rietveld structural refinement, photoluminescence spectroscopy and measurement of fluorescence decay lifetimes. The NBAC: Eu2+ and NBAB: Eu2+ phosphors exhibited broad excitation ranging from 250 to 420 nm, both of which overlapped well with the emission of n-UV LED chips. Under 365 nm excitation, intense asymmetric blue emission bands were obtained for NBAC: Eu2+ and NBAB: Eu2+, peaking around 429 and 437 nm, respectively. The optimal Eu2+ doping concentration in both NBAC: xEu(2+) and NBAB: xEu(2+) was determined to be the same (10 mol%). The concentration quenching mechanism turned out to be electric dipole-dipole interactions. The NBAB: 0.1Eu(2+) and NBAC: 0.1Eu(2+) phosphors presented superior blue-emitting properties to the commercially available BAM: Eu2+ blue phosphor. The optimized NBAB: 0.1Eu(2+) and NBAC: 0.1Eu(2+) exhibited high external quantum efficiencies of 98.7% and 74.7% of the commercially available compound BaMgAl10O17: Eu2+ (BAM: Eu2+), respectively, while the NBAB: 0.1Eu(2+) phosphor demonstrated a very narrow band (FWHM <= 33 nm) and an ultra-high color purity of 99.58%. These results suggest that NBAB: Eu2+ and NBAC: Eu2+ can serve as promising blue-emitting candidates for n-UV pumped white LEDs.