Effects of host composition, Al3+ as a sensitizer and SiO2 surface coating on luminescence intensity, color purity of MVO4: Al3+, Eu3+ @ SiO2 (M = Gd, Y and Gd/Y) red phosphors

MVO4: Al3+, Eu3+@ SiO2 powder phosphors have been synthesized by a modified colloidal precipitation technique followed by calcination. Luminescence optimization was fine tuned mainly in three stages, by investigating the effects of: (i) host composition (Gd, Y and Gd/Y), (ii) co-dopant Al3+ as a sensitizer and finally (iii) with SiO2 coating as a surface protecting layer. XRD data revealed that the produced phosphors were well crystalline and possess body centered tetragonal phase. SEM micrographs illustrate that the synthesized phosphor particles are loosely bound with tetragonal like morphology and consists 1–5 μm dia grain size. Silica coating on phosphor particles were characterized by SEM/EDAX, TEM, FT-IR and PL measurements. An intense charge transfer excitation band owing to VO43− has dominated the f–f transitions of Eu3+ ions. The emission intensities of the hypersensitive 5D0 → 7F2 transitions are stronger than the magnetic dipole 5D0 → 7F1, indicates lowering of inversion symmetry in the vicinity of Eu3+, ions. Red color richness owing to the efficient energy transfer from Al3+ to Eu3+ with Y0.94VO4: Al3+0.01, Eu3+0.05 phosphor were enhanced significantly by 3 times stronger than the phosphor Y0.95VO4: Eu3+0.05, which was further increased 1.2 times with SiO2 protecting layer.