Site occupation engineering of activator in a green phosphor Sr8CaLu(PO4)7: Eu2+ with high quantum yield for solid state lighting

Abstract

The site occupation engineering of activators in the phosphor directly affects its luminescence properties; thus, revealing the relationship between the site occupation and the activator luminescence is of great significance. In this work, a high efficiency green phosphor Sr8CaLu(PO4)7: Eu2+ (SCLP: Eu2+) was successfully constructed based on the model of whitlockite β-Ca3(PO4)2 host, and its phase structure, morphology features and optical properties were systemically investigated. The as-prepared SCLP: Eu2+ phosphor had a monoclinic symmetry and a broad green emission from 420 to 730 nm with a quantum yield as high as 77%. The SCLP host offered five types of Sr2+ ions sites for Eu2+ ions occupation; and the PL spectra were divided into three sub-peaks locating at 501 (19960.08 cm−1), 527 (18975.33 cm−1) and 566 nm (17667.84 cm−1), which were proved to the emission of Eu2+ ions at the nine-coordinated Sr(1, 3, 5)O9, eight-coordinated Sr(2)O8 and special vacant Sr(4)O6 sites, respectively. The thermal stability was improved through the package of SiO2, and the activation energy was enhanced from 0.1098 to 0.1457 eV. Eventually, the SCLP: xEu2+ phosphors were applied in white light-emitting diode, showing high color rendering index (Ra = 94.4 and R9 = 81.7) and moderate correlated color temperature (CCT = 4902 K). This work could help to understand the mechanism behind the site-controlled activator emission and offer some meaningful ideas to design a new whitlockite phosphor with desirable spectral emission for application in high quality lighting source.