Fig. 2: Characterization of core@shell@shell SiO₂ microparticles (MPs) doped with 4-PP, 1,8-NP, and 4,4’-BP in their core, first shell, and second shell layers, respectively.

a TEM image. The inset displays a typical HRTEM image of a selected core@shell@shell SiO₂ MP. Scale bar: 50 nm. b Size distributions of the core, core@shell, and core@shell@shell SiO₂ MPs. Note that 200 MPs were used in the average size examination. c Excitation-afterglow mapping of an ethanol dispersion of the as-prepared core@shell@shell SiO₂ MPs (10 mg/mL). d–f Photoluminescence (upper panel) and afterglow emission (lower panel) of the ethanol dispersion of core@shell@shell SiO₂ MPs under excitation at 250, 290, and 350 nm. Gated time: 2 ms. Insets show the dopants under the corresponding excitations. g–i Decay curves at 435 nm for 4,4’-BP under excitation at 250 nm, 472 nm for 4-PP under excitation at 290 nm, and 546 nm for 1,8-NP under excitation at 350 nm. j Photographs of ethanol dispersions under excitation at 254 nm, 310 nm, and 365 nm, and after the corresponding excitations.