Extended Data Fig. 1: Synthesis and characterization of Tb³⁺-doped nanocrystals.

a, Schematic for the synthesis of NaLuF₄:Ln/Gd (Ln = Pr³⁺, Sm³⁺, Ho³⁺, Er³⁺, Tb³⁺, Dy³⁺, Tm³⁺ and Nd³⁺) nanocrystals. In a typical procedure, lanthanide acetate salts (Ln(Ac)₃•xH₂O) were added to a flask containing OA and ODE. The mixture was heated at 150 °C to form lanthanide–oleate coordination complexes. Nucleation of NaLuF₄:Ln/Gd nanocrystals was triggered by injecting a methanol solution of NaOH and NH₄F. Subsequently, the reaction solution was heated at 300 °C for 1 h. The final product was precipitated with ethanol. OA was used as a surface ligand to control the particle size and stabilize as-synthesized nanocrystals. b–f, Low-resolution TEM images of as-synthesized hexagonal-phase nanocrystals (top) and corresponding size distributions (bottom). These samples are NaLuF₄:Tb/Gd (15/35 mol%) (b), NaLuF₄:Tb/Gd (15/25 mol%) (c), NaLuF₄:Tb/Gd (15/15 mol%) (d), NaLuF₄:Tb/Gd (15/5 mol%) (e) and NaLuF₄:Tb (15 mol%) (f). Scale bars, 200 nm. g, Particle size as a function of the lutetium doping ratio. h, Powder X-ray diffraction patterns for NaLuF₄:Tb/Gd (15/x mol%; x = 0–35) nanocrystals. All peaks are consistent with the hexagonal-phase NaLuF₄ structure (Joint Committee on Powder Diffraction Standards (PDF) file number 27-0726). i, Corresponding persistent radioluminescence decay curves of NaLuF₄:Tb/Gd (15/x mol%; x = 0–35) nanocrystals monitored at 546 nm as a function of time. Spectra were obtained after X-ray excitation at a power density of 278 μGy s⁻¹ for 5 min at room temperature (298 K).