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

Abstract

Highly efficient blue-emitting NaBa₄(AlB₄O₉)₂X₃ (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:xEu²⁺ and NBAB:xEu²⁺ was determined to be the same (10 mol%). The concentration quenching mechanism turned out to be electric dipole–dipole interactions. The NBAB:0.1Eu²⁺ and NBAC:0.1Eu²⁺ phosphors presented superior blue-emitting properties to the commercially available BAM:Eu²⁺ blue phosphor. The optimized NBAB:0.1Eu²⁺ and NBAC:0.1Eu²⁺ exhibited high external quantum efficiencies of 98.7% and 74.7% of the commercially available compound BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺), respectively, while the NBAB:0.1Eu²⁺ 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.