fig2

Figure 2. (A) Room-temperature UCL spectra of Cs₂ZrF₆:Yb/Er NCs doped with different Li⁺ content under 980 nm excitation; (B) Integrated green and red emission intensity of Cs₂ZrF₆:Yb/Er NCs doped with different Li⁺ content; (C) Evolution of the UCL enhancement factor for the CZF-Li-X NCs and their corresponding nanocrystal sizes as a function of Li⁺ doping content; (D) CIE (x,y) chromaticity diagram showing the color change with increasing Li⁺ content from 0 to 38 mol%. The inset shows their corresponding photographs obtained by a Canon digital camera; (E) Lifetimes of Er³⁺ monitored at 656 nm for the CZF-Li-X NCs under 980 nm excitation; (F) Comparison of SAED patterns for the CZF-Li-0, CZF-Li-35, and CZF-Li-38 NCs, illustrating different degrees of crystallinity improvement with increasing Li⁺ doping; (G) Power-dependent UCL spectra of the CZF-Li-38 NCs and (H) corresponding pump power dependence of green and red emission intensities. UCL: Upconversion luminescence; NCs: nanocrystals; CZF-Li-X NCs: Cs₂ZrF₆:Yb/Er NCs with and without Li⁺-doping; CIE: Commission Internationale de l’Éclairage; SAED: selected area electron diffraction.