Single-component materials with white-light emission are ideal for lighting applications. However, it is very challenging to achieve white luminescence in single-dopant activated solid phosphors. Herein, white NaLi 3 Si 1− x O 4 :Eu 2+ materials are designed via defect engineering and synthesized by reducing the Si content (0.15 ≤ x ≤ 0.25). Stochiometric NaLi 3 SiO 4 :Eu 2+ exhibits a narrow-band blue emission at 469 nm, ascribed to the 5d → 4f transition of Eu 2+ at highly symmetric cuboid Na sites, while samples with Si content reduced by 15–25% display white emission with two peaks at 472 nm and 585 nm. The newly appeared broadband yellow peak arises from charge-transfer transitions involving Eu 2+ and nearby defects, as verified by an unusual bandwidth, a large Stokes shift, and a long decay time. A single-component white light-emitting diode device is fabricated by employing a white phosphor to demonstrate a color-rendering index of 82.9. This result provides a new design strategy for single-component white-light materials with broad-band defect-induced charge-transfer emission.
Jun Sun,Bei Zhang,Wei Zhu,Feifei Huang,Ruoshan Lei,Hongping Ma,Renguang Ye,Youjie Hua,Shiqing Xu
High-efficiency phosphor with excellent luminescence properties and thermal stabilities is essential for phosphor-converted white light-emitting diodes (w-LEDs). Compared with red and green phosphors, near-ultraviolet excited blue phosphors with high efficiency and excellent thermal stability are still scarce, and the development of efficient blue phosphors remains challenging. NaLi 3 SiO 4 : Eu 2+ (NLSO: Eu 2+ ) is a promising narrow-band blue phosphor. In this paper, a series of Na 1-y K y Li 3 SiO 4 : 5%Eu 2+ (0.05 ≤ y ≤ 0.2) phosphors were successfully synthesized by high-temperature solid-state reaction through co-doping a small amount of K + ions in the matrix, significantly improving their luminescence property and thermal stability. Because of the weaker electronegativity of K + ions, the emission peaks of Na 1-y K y Li 3 SiO 4 : 5%Eu 2+ were slightly blue-shifted from 467 to 463 nm compared with those of NLSO: Eu 2+ . With an increase in the number of K + ions, the luminescence intensity of the phosphors increased. When the content of the K + ion reached 0.2, the luminescence intensity of the Na 0.8 K 0.2 Li 3 SiO 4 : 5%Eu 2+ (NKLSO: 5%Eu 2+ ) phosphor reached its maximum. Compared to the NLSO: 5%Eu 2+ phosphor, the luminescence intensity increased by approximately 300 %. At 150 °C, the luminescence intensity of NLSO: 5%Eu 2+ phosphor was retained at 75.98 % compared with room temperature , while the NKLSO: 5%Eu 2+ phosphor maintained a luminescence intensity of 84.36 % relative to room temperature, demonstrating excellent thermal stability. The enhanced luminescence performance of the NKLSO: Eu 2+ phosphor makes it a promising high-efficiency blue phosphor for phosphor-converted w-LEDs.
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