Growth of Highly Crystalline CaMoO₄:Tb³⁺ Phosphor Layers on Spherical SiO₂ Particles via Sol−Gel Process:  Structural Characterization and Luminescent Properties

Highly crystalline CaMoO4:Tb3+ phosphor layers were grown on monodisperse SiO2 particles through a simple sol−gel method, resulting in formation of core−shell structured SiO2@CaMoO4:Tb3+ submicrospheres. The resulting SiO2@CaMoO4:Tb3+ core−shell particles were fully characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), and kinetic decays. The XRD results demonstrate that the CaMoO4:Tb3+ layers begin to crystallize on the SiO2 spheres after annealing at 400 °C and the crystallinity increases with raising the annealing temperature. SEM and TEM analysis indicates that the obtained submicrospheres have a uniform size distribution and obvious core−shell structure. SiO2@CaMoO4:Tb3+ submicrospheres show strong green emission under short ultraviolet (260 nm) and low-voltage electron beam (1−3 kV) excitation, and the emission spectra are dominated by a 5D4−7F5 transition of Tb3+ (544 nm, green) from the CaMoO4:Tb3+ shells. Moreover, the PL intensities of Tb3+ increase with increasing annealing temperature and number of coating cycles. The optimum concentration for Tb3+ was determined to be 5 mol % of Ca2+ in CaMoO4 host shells.