Fig. 1. Preparation flow chart of BEDF. (a) Preparation process of BEDF; (b) reaction of ALD deposition

Fig. 2. Cross-section and refractive index distribution of BEDF

Fig. 3. Spectrum testing systems. (a) Transmission spectra measurement; (b) luminescence spectra measurement

Fig. 4. Transmission spectra of BEDF at different stretching lengths (diameters)

Fig. 5. Luminescence spectra of BEDF under different pumping powers

Fig. 6. Luminescence spectra of BEDF at different stretching lengths (diameters)