fig3

Figure 3. (A) UCL spectra of the CZF-Li-38 NCs as a function of temperature in the range of 303-483 K under 980 nm excitation and their corresponding (B) UCL R/G ratios; (C) CIE (x,y) and corresponding zoomed-in chromaticity diagrams of the emission colors from the CZF-Li-38 NCs with an increase in temperature; (D) Contour map of thermal evolution spectra and (E) temperature dependence of the luminescent enhancement factor for the CZF-Li-38 NCs; (F) Lifetimes of Er³⁺ emission monitored at 656 nm under 980 nm excitation; (G) In situ temperature-dependent XRD patterns of the CZF-Li-38 NCs from 303 to 483 K, and the right panel shows the evolution of (101) diffraction peak; (H) Energy level diagram revealing the proposed energy transfer processes for the CZF-Li-38 NCs under 980 nm excitation. UCL: Upconversion luminescence; CZF-Li-X NCs: Cs₂ZrF₆:Yb/Er NCs with and without Li⁺-doping; NCs: nanocrystals; XRD: X-ray diffraction; CE: captured electrons; RE: released electrons; CR: cross relaxation; CIE: Commission Internationale de l’Éclairage.