Structure dependent luminescence characterization of green–yellow emitting Sr2SiO4:Eu2+ phosphors for near UV LEDs

This paper reports on the luminescence properties of mixtures of α- and β-(Sr0.97Eu0.03)2SiO4 phosphors. These phosphors were prepared by 3 different synthesis techniques: a modified sol–gel/Pechini method, a co-precipitation method and a combustion method. The structural and optical properties of these phosphors were compared to those of solid state synthesized powders. The emission spectra consist of a weak broad blue band centered near 460 nm and a strong broad green–yellow band centered between 543 and 573 nm depending on the crystal structure. The green–yellow emission peak blue-shifts as the amount of β phase increases and the photoluminescence emission intensity and quantum efficiency of the mixed phase powders is greater than those of predominant α-phase powders when excited between 370 and 410 nm. Thus, (Sr1−xEux)2SiO4 with larger proportion of the β phase are more promising candidates than single α-phase powders for use as a green–yellow emitting phosphor for near UV LED applications. Finally the phosphors prepared by the sol–gel/Pechini method, which have larger amount of β phase, have a higher emission intensity and quantum efficiency than those prepared by co-precipitation or combustion synthesis.