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 alpha- and beta-(Sr0.97Eu0.03)(2)SiO4 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 beta phase increases and the photoluminescence emission intensity and quantum efficiency of the mixed phase powders is greater than those of predominant alpha-phase powders when excited between 370 and 410 nm. Thus, (Sr0.97Eu0.03)(2)SiO4 with larger proportion of the beta phase are more promising candidates than single alpha-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 beta phase, have a higher emission intensity and quantum efficiency than those prepared by co-precipitation or combustion synthesis. (C) 2011 Elsevier B.V. All rights reserved.