Impact of surface coating on physical properties of europium-doped gadolinium fluoride microspheres

Abstract

A facile polyol with co-precipitation method was utilized for preparation of GdF3:Eu microspheres (core-MSs) at low temperature. The as-prepared core-MSs were successfully coated with lanthanum fluoride and silica shells to enhance the luminescence and solubility characters of the nanomaterials. The as-prepared core and GdF3:Eu@LaF3 (core/shell) MSs possess pure orthorhombic structure, which was spherically shaped with the average crystalline size of about 400nm. Energy dispersive x-ray (EDX) analysis confirms the composition and doping of the europium ion into the nanomaterial lattice. On comparing the luminescence properties under same experimental conditions, the excitation and emission intensity of core/shell MSs was remarkably enhanced due to a reduction in nonradiative transition decay. However, the luminescence intensity in silica surface modified GdF3:Eu@LaF3@SiO2 (core/shell/SiO2) MSs was quenched in respect to core and core/shell MSs, causing the presence of abundant surface SiOH molecules, which are responsible for enhancing the multiphonon relaxation rate. However, these silanol groups greatly improve the solubility character in an aqueous and non-aqueous solvent. The observed results indicate that the significant improvement in solubility of as-prepared silica modified core/shell/SiO2 MSs can be used more desirable luminescent lanthanides nanocrystals for photonic based bio-applications.