Large-Scale Nanofiber Manufacturing| A facile neoteric technique to achieve[SrF,:Eu3+@Si0,1//[SrF,:Tb3+@sio,] Janus yolk-shell nanofibers with ideal white-light emission viatriple-inhibiting energy transfer between Tb3+ andEu3+ ionst

 Prof. Dong Xiangting at CUST JMCC: Achieving Ideal White-Light Emission Through Triple-Inhibiting Energy Transfer Approach

With the rapid development of white-light emitting diodes (LEDs), white-light LED materials play important roles in lighting, displays, and optoelectronic devices. However, strong luminescent materials co-doped with Eu³⁺ and Tb³⁺ hardly achieve white-light emission due to energy transfer (ET) between them. By inhibiting ET from Tb³⁺ to Eu³⁺ while enhancing Tb³⁺'s green emission, white light can be easily obtained.

Recently, Prof. Dong Xiangting's team at Changchun University of Science and Technology published their findings in Journal of Materials Chemistry C titled "A facile neoteric technique to achieve [SrF₂:Eu³⁺@SiO₂]//[SrF₂:Tb³⁺@SiO₂] Janus yolk-shell nanofibers with ideal white-light emission via triple-inhibiting energy transfer between Tb³⁺ and Eu³⁺ ions". The researchers proposed an innovative triple-inhibiting ET method to completely suppress ET between Tb³⁺ and Eu³⁺ in Janus yolk-shell nanofibers (JYSNFs), achieving ideal white-light emission.Figure 1 illustrates the preparation process and formation mechanism of [SrF₂:Eu³⁺@SiO₂]//[SrF₂:Tb³⁺@SiO₂] JYSNFs. This design concept provides theoretical and technical support for developing novel rare-earth luminescent materials. Ph.D. candidate Li Ning is the first author, with Prof. Dong as corresponding author.

As shown in Figure 2, all samples exhibit excellent fiber morphology. Two nanofibers combine side-by-side forming smooth Janus composite nanofibers (Fig. 2a). After calcination, clear yolk-shell structures appear on both sides, forming well-dispersed JYSNFs (Fig. 2b). TEM images (Fig. 2c) reveal obvious gaps between inner/outer layers, confirming the unique Janus yolk-shell structure. In contrast, blended composite fibers show smooth surfaces (Fig. 2d), while yolk-shell nanofibers (YSNFs) also demonstrate clear structures (Figs. 2e-f).

To verify JYSNFs' superiority, Eu³⁺ concentration was fixed at 9%. Figure 3a shows Tb³⁺'s 545 nm emission increases with doping concentration while Eu³⁺'s 592 nm emission remains unchanged, confirming suppressed ET. Under 393 nm excitation (Fig. 3b), only Eu³⁺ emission appears without intensity variation. These results prove spatial separation effectively inhibits ET, enabling white-light emission (Fig. 4a).

Comparative YSNFs with 9% Eu³⁺ show enhanced emissions for both ions under 252 nm excitation (Fig. 3c), with maximum Eu³⁺ emission at 7% Tb³⁺ under 393 nm (Fig. 3d), confirming ET occurrence and yellow emission (Fig. 4b), highlighting JYSNFs' advantages.

To further study the luminescent color of the samples, under 252 nm ultraviolet light excitation, the luminescent color of JYSNFs shifted from the green light region to the white light region by adjusting the content of Tb³⁺ ions (Fig. 4a), especially achieving ideal white light emission (0.3301, 0.3285). In contrast, the contrast sample YSNFs exhibited yellow fluorescence (Fig. 4b). This is because in the presence of ET between Tb³⁺ and Eu³⁺, Tb³⁺ ions emit weak blue-green light, while Eu³⁺ ions emit strong red light, resulting in the final sample exhibiting yellow luminescence. Additionally, under 393 nm light excitation, the luminescent colors of JYSNFs all fell within the yellow light region (Fig. 4c). In contrast, the fluorescence color of the contrast sample YSNFs shifted from dark yellow to light yellow due to the ET from Tb³⁺ to Eu³⁺ (Fig. 4d). These results further demonstrate the superiority of the Janus yolk-shell structure.