文摘
Phosphors with sufficient red emission component are necessary for warm white light-emitting diodes. In this work on (Sr,Ba)<sub>2(1–x)sub>Eu<sub>2xsub>SiO<sub>4sub> phosphors, (Sr,Ba)<sub>1.5sub>Eu<sub>0.5sub>SiO<sub>4sub> achieved 75% of an internal quantum efficiency under excitation by blue light. Surprisingly, the (Sr,Ba)<sub>1.5sub>Eu<sub>0.5sub>SiO<sub>4sub> exhibited orange emission, against the well-known traditional green-yellow emission of (Sr,Ba)<sub>2sub>SiO<sub>4sub>:Eu<sup>2+sup>. Moreover, the concentration quenching of Eu<sup>2+sup> in (Sr,Ba)<sub>2sub>SiO<sub>4sub> was abnormally unobvious. With the help of calculations based on the density functional theory, it was discovered that the distinct local environment of luminescence centers rather than usual explanation such as self-absorption or intensified crystal field splitting, is responsible to the interesting red shifts in excitation and emission spectra. The refinement analysis based on X-ray diffraction revealed that the unequal distribution of Eu<sup>2+sup> to two crystallographic sites caused low concentration of Eu<sup>2+sup> at the 9-coordination site, inhibiting the concentration quenching. The (Sr,Ba)<sub>1.5sub>Eu<sub>0.5sub>SiO<sub>4sub> phosphor has warmer emission than the commercial Y<sub>3sub>Al<sub>5sub>O<sub>12sub>:Ce<sup>3+sup>. This study also promotes research on the effect of site occupancy and the local environment of luminescence centers.