Thin films of silica particles covered with lanthanide substituted Keggin polyoxometalates and their optical properties

In this paper, the chemical grafting method has been adopted to prepare hybrid core–shell particles by covering the surfaces of monodisperse uniform silica with lanthanides–polyoxometalates Ka (EuXWO39)2 (X = Si, B, a = 13 or 15) shells, respectively. The thin films of core/shell polyoxometalates/silica particles were successfully fabricated by standard spin-coating method. The hybrid core–shell particles and thin films were characterized by IR, UV–vis spectra, scanning electron microscopy and luminescent spectra, respectively. The hybrid core–shell particles show the strong luminescence which could be seen by naked eyes. The excitation spectrum of thin film of polyoxometalate/silica particles show the ligand to metal charge transfer band, which could be not seen in the excitation spectrum of lanthanides–polyoxometalate. The ratios of the electronic dipole 5D0 → 7F2 transitions to the magnetic dipole 5D0 → 7F1 ones in the emission spectra of thin films have changed, which indicated the various symmetry of sites occupied by Eu3+ ions in thin films.