Fig. 1: PersL enhancement by the surface-passivated core–shell structure

a Schematic illustration of the core–shell structure and proposed PersL enhancement mechanism. The description of particle components is given on the right side. b–c TEM images of NaYF₄:Tb³⁺ and NaYF₄:Tb³⁺@NaYF₄ nanoparticles. The insets show the particle size distributions of the nanoparticles. d–f RL spectra (d), TL glow curves (e) and PersL decay curves (f) of NaYF₄:Tb³⁺ and NaYF₄:Tb³⁺@NaYF₄ monitored in the range of 400–750 nm. The insert of (f) shows the PersL images of NaYF₄:Tb³⁺ and NaYF₄:Tb³⁺@NaYF₄ dispersed in cyclohexane. g–i RL spectra (g), TL glow curves (h) and PersL decay curves (i) of NaYF₄:Nd³⁺ and NaYF₄:Nd³⁺@NaYF₄ monitored in the range of 400–1000 nm. The RL spectra in (d) and (g) were measured under X-ray excitation. The TL glow curves in (e) and (h) as well as the PersL decay curves in (f) and (i) were recorded after X-ray irradiation for 5 min