Fig. 1. Experimental results. (a) X-ray diffraction spectra of precursor glass PG and glass ceramics GC660 samples and NaYb₂F₇ standard card (PDF No.: 43-1126); (b) transmittance spectra of precursor glass and glass ceramics GC660 samples

Fig. 2. Electron microscopy. (a) Transmission electron microscopy of GC660 sample; (b) high resolution transmittance electron microscopy of GC660 sample; (c) high angle annular dark field-scanning transmission electron microscopy and (d) F, (e) Na, (f) Y, and (g) Eu elements distribution of GC660 samples

Fig. 3. Spectra. (a) Excitation and emission spectra of Eu²⁺ in PG and GC660 samples (λ_em=425 nm, λ_ex=340 nm); (b) excitation and emission spectra of Eu³⁺ in PG and GC660 samples (λ_em=613 nm, λ_ex=393 nm)

Fig. 4. Decay curves of Eu²⁺ and Eu³⁺ in PG and GC660 sample. (a) 5d→4f transition of Eu²⁺; (b) ⁵D₀→⁷F₂ transition of Eu³⁺

Fig. 5. Spactra. (a) Excitation spectra of Eu³⁺ (λ_em=613 nm) and emission spectra of Eu²⁺(λ_ex=350 nm); (b) excitation spectra of Eu³⁺ (λ_em=613 nm) and Eu²⁺ (λ_em=425 nm)

Fig. 6. Emission spectra of PG and GC660 under excitation of 344 nm

Fig. 7. Results of GC660 samples excited by different excitation wavelengths (340‒400 nm). (a) Emission spectra; (b) CIE coordinate plots

Fig. 8. Experimental results. (a) Temperature-dependent spectra of GC660 samples (λ_ex=380 nm); (b) relationship between relative integrated emission intensities of Eu²⁺ and Eu³⁺ and temperature