Effects of host composition, Al~(3+) as a sensitizer and SiO_2 surface coating on luminescence intensity, color purity of MVO_4: Al~(3+), Eu~(3+) @ SiO_2 (M = Gd, Y and Gd/Y) red phosphors

摘要

MVO_4: Al~(3+), Eu~(3+)@ SiO_2 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 Al~(3+) as a sensitizer and finally (ⅲ) with SiO_2 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 urn 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 VO_4~(3-) has dominated the f-f transitions of Eu~(3+) ions. The emission intensities of the hypersensitive ~5D_0→7F_2 transitions are stronger than the magnetic dipole ~5D_0→7F_1, indicates lowering of inversion symmetry in the vicinity of Eu~(3+), ions. Red color richness owing to the efficient energy transfer from Al~(3+) to Eu~(3+) with Y_(0.94)VO_4: Al_(0.01)~(3+). Eu~(3+)o.o5 phosphor were enhanced significantly by 3 times stronger than the phosphor Y_(0.95)VO_4: Eu_(0.05)~(3+), which was further increased 1.2 times with SiO_2 protecting layer.