title: Anomalous Orange Light-Emitting (Sr,Ba)2SiO4:Eu(2+) Phosphors for Warm White LEDs.
abstract: Phosphors with sufficient red emission component are necessary for warm white light-emitting diodes. In this work on (Sr,Ba)2(1-x)Eu2xSiO4 phosphors, (Sr,Ba)1.5Eu0.5SiO4 achieved 75% of an internal quantum efficiency under excitation by blue light. Surprisingly, the (Sr,Ba)1.5Eu0.5SiO4 exhibited orange emission, against the well-known traditional green-yellow emission of (Sr,Ba)2SiO4:Eu(2+). Moreover, the concentration quenching of Eu(2+) in (Sr,Ba)2SiO4 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(2+) to two crystallographic sites caused low concentration of Eu(2+) at the 9-coordination site, inhibiting the concentration quenching. The (Sr,Ba)1.5Eu0.5SiO4 phosphor has warmer emission than the commercial Y3Al5O12:Ce(3+). This study also promotes research on the effect of site occupancy and the local environment of luminescence centers.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Sendai 980-8577, Japan.
authors.forename: Dawei
authors.initials: D
authors.lastname: Wen
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Sendai 980-8577, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kuwahara
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Sendai 980-8577, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kato
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Sendai 980-8577, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Kobayashi
authors.affiliation: Faculty of Science, Okayama University of Science , Okayama 700-0005, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Sato
authors.affiliation: School of Advanced Material Science and Engineering, Sungkyunkwan University , Suwon 440-746, Republic of Korea.
authors.forename: Takaki
authors.initials: T
authors.lastname: Masaki
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Sendai 980-8577, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Kakihana
keywords: color tuning; orange emission; phosphor; site occupancy; white LED