Extended Data Fig. 2: Optimize the doping concentration of Yb³⁺, Nd³⁺, Er³⁺, and Tm³⁺ in Na₃CrF₆:X nanoparticles.

a, Schematic for the synthesis of Na₃CrF₆:X (X = Yb³⁺, Nd³⁺, Er³⁺, and Tm³⁺) nanoparticles. Insets: The optical photograph of Na₃CrF₆:Er nanoparticles. b-e, TEM images for Na₃CrF₆:Yb (3.5 mol%) (b), Na₃CrF₆:Nd (5.6 mol%) (c), Na₃CrF₆:Er (4.2 mol%) (d), and Na₃CrF₆:Tm (4.1 mol%) (e) nanoparticles, respectively. f-i, Typical emission and excitation spectra of Na₃CrF₆:Yb (3.5 mol%) (f), Na₃CrF₆:Nd (5.6 mol%) (g), Na₃CrF₆:Er (4.2 mol%) (h), and Na₃CrF₆:Tm (4.1 mol%) (i) nanoparticles, respectively. j-m, Influence of activator concentration on the luminescence intensity of Yb³⁺ (j), Nd³⁺ (k), Er³⁺ (l), and Tm³⁺ (m) in Na₃CrF₆:X nanoparticles, respectively. All measurements were performed three times. The data are shown as the mean ± s.d. n-q, The relationship of Yb³⁺ (n), Nd³⁺ (o), Er³⁺ (p), and Tm³⁺ (q) concentration for ICP-OES tested and fed in the synthesis of Na₃CrF₆:X (X = Yb³⁺, Nd³⁺, Er³⁺, and Tm³⁺) nanoparticles, respectively. Scale bar: 100 nm. All measurements were performed three times. The data are shown as the mean ± s.d.

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