Spherical red-emitting X1-Y2SiO5:Eu and α-Y2Si2O7:Eu phosphors with high color purity: The evolution of morphology, phase and photoluminescence upon annealing

Spherical silicate phosphor has widespread application in display or lighting industry. By using spherical silica particles as the core, we successfully prepared shell-thickness-controllable core/shell spherical particles, which can then be controllably converted to spherical X-1-Y2SiO5:Eu (YSO:Eu) and alpha-Y2Si2O7:Eu (YPS:Eu) particles upon annealing. Even after 1000-1200 degrees C annealing, both X-1-YSO:Eu and alpha-YPS:Eu particles still had the spherical shape and narrow size distribution. The shell thickness and annealing temperature synergistically controlled the phase evolution upon annealing. Thinner shell of around 30 nm, having extremely high chemical reaction activity, promoted the formation of spherical X-1-YSO:Eu particles at 1000 degrees C and alpha-YPS:Eu particles at 1100 degrees C. Shell of around 85 nm produced spherical X-1-YSO:Eu particles at 1100 degrees C and alpha-YPS:Eu particles at 1200 degrees C. Thicker shell also promoted the formation of spherical particles, but these particles usually had the mixed silicate phases. The phase-dependent photoluminescence properties were investigated in detail. Both spherical X-1-YSO: Eu and alpha-YPS:Eu phosphors emitted reddish-orange color, with nearly 100% color purity and dominant wavelength of around 601 nm, which would absorb great attention for the application in display or lighting devices.