Realizing cool and warm white-LEDs based on color controllable (Sr,Ba)2Al3O6F:Eu2+ phosphors obtained via a microwave-assisted diffusion method

Abstract

Globally, phosphor converted white-LEDs (W-LEDs) are among the most suitable sources to reduce energy consumption. Nevertheless, modernization of efficient broadband emitting phosphors is most crucial to improve the W-LED performance. Herein, we synthesized a series of novel broadband emitting Sr_2−xAl₃O₆F:xEu²⁺ phosphors via a new microwave-assisted diffusion method. Rietveld refinement of the obtained X-ray diffraction results was performed to recognize the exact crystal phase and the various cationic sites. Oxygen vacancies (V^O) formed under synthetic reducing conditions enabled Sr₂Al₃O₆F to demonstrate bright self-activated bluish emission. Doping of Eu²⁺ ions unlocked the energy transfer process from the host to the activator ions, owing to which, the self-activated emission diminished and the Eu²⁺-doped sample showed amplified bluish-green emission. The gradual increase in Eu²⁺ concentrations regulated the controllable emissions from the bluish (0.34, 0.42) to the greenish (0.38, 0.43) zone under UV excitation. Because of the different absorption preferences of Eu²⁺ ions located at the different Sr²⁺ sites, Sr_2−xAl₃O₆F:xEu²⁺ exhibited bluish-white emission under blue irradiation. A further enhancement in PL intensity had been observed by the cation substitution of Ba²⁺ for Sr²⁺ sites in the optimum Sr_1.95Al₃O₆F:0.05Eu²⁺ phosphor. The as-fabricated W-LEDs utilizing the optimized Sr_1.75Ba_0.2Al₃O₆F:0.05Eu²⁺ phosphor exhibited a cool-white light emission along with a 372 nm NUV-LED and a 420 nm blue-LED with a moderate CRI of 70 and a CCT above 6000 K. Such cool white emission was controlled to natural white with the CCT close to 5000 K, and the CRI above 80 via utilizing a suitable red emitting phosphor. The W-LED performances of the optimized phosphor justified its applicability to produce white light for lighting applications.