Phosphor-free silica-coating of monodisperse cores for dual functionalization with luminescent and mesoporous shell

Abstract

To dually functionalize monodisperse cores with luminescence and mesopores, hydrolysis and condensation of tetraethyl orthosilicate in the presence of a double chain cationic surfactant of didodecyldimethylammonium bromide (DDAB) were applied to monodisperse silica cores with an average size smaller than 100 nm. Highly monodisperse core-shell particles were obtained by uniform coating of the cores with silica shell. Calcination of the silica shell at 500 °C to remove the incorporated DDAB surfactant provided the shells with mesoporous and luminescent properties without using any phosphors. The size of mesopores could be expanded by using dihexadecyldimethylammonium bromide (DHAB) with alkyl chains longer than DDAB. The combination of silica shell formation and calcination was also applied to monodisperse polymer cores, which created monodisperse, luminescent, hollow mesoporous silica particles (HMSs) with a sub-100 nm cavity inside. The emission intensity of mesoporous shell measured with an excitation wavelength of 365 nm could be sharply increased by an increase in the volume of mesoporous shell formed on the silica cores, implying that the luminescent centers derived from organic residue homogeneously distributed in the mesoporous shell.