Realizing cool and warm white-LEDs based on color controllable (Sr,Ba)AlOF:Eu phosphors obtained a microwave-assisted diffusion method

• Published in: Physical chemistry chemical physics : PCCP Vol. 23; no. 28; pp. 15245 - 15256
• Main Authors: Ranjith, P, Sreevalsa, S, Patra, Pritha, Som, Sudipta, Menon, Ammu, Jayanthi, K, Annapurna, K, Krishnan, N. M. Anoop, Allu, Amarnath R, Das, Subrata
• Format: Journal Article
• Published: 21.07.2021
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp01593a

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− x Al 3 O 6 F: x Eu 2+ 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 Sr 2 Al 3 O 6 F to demonstrate bright self-activated bluish emission. Doping of Eu 2+ ions unlocked the energy transfer process from the host to the activator ions, owing to which, the self-activated emission diminished and the Eu 2+ -doped sample showed amplified bluish-green emission. The gradual increase in Eu 2+ 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 Eu 2+ ions located at the different Sr 2+ sites, Sr 2− x Al 3 O 6 F: x Eu 2+ exhibited bluish-white emission under blue irradiation. A further enhancement in PL intensity had been observed by the cation substitution of Ba 2+ for Sr 2+ sites in the optimum Sr 1.95 Al 3 O 6 F:0.05Eu 2+ phosphor. The as-fabricated W-LEDs utilizing the optimized Sr 1.75 Ba 0.2 Al 3 O 6 F:0.05Eu 2+ 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. A broadband emitting Sr 1.75 Ba 0.2 Al 3 O 6 F: 0.05Eu 2+ phosphor emitting cool white light under NUV (Fig. a(i)) and blue LEDs (Fig. b(i)). With a preferred red phosphor, this system produced natural white light with a higher CRI (Fig. a(ii) & b(ii).