Electronic structure and photoluminescence properties of Eu-activated Ca4Si2O7F2

The blue-emitting phosphors Ca_(4−x)Eu_xSi₂O₇F₂ (0 < x ? 0.05) have been prepared by solid-state reaction and the photoluminescence properties have been studied systematically. The electronic structure of calcium fluoride silicate Ca₄Si₂O₇F₂ was calculated using the CASTEP code. The calculation results of electronic structure show that Ca₄Si₂O₇F₂ has an indirect band gap with 5 eV. The top of the valence band is dominated by O 2p and Si 3p states, while the bottom of the conduction band is mainly composed of Ca 3d states. Under the 350 nm excitation, the obtained sample shows a broad emission band in the wavelength range of 400-500 nm with peaks of 413 nm and 460 nm from two different luminescence centers, respectively. The relative intensity of the two peaks changes with the alteration of the Eu²⁺ concentration. The strong excitation bands of the powder in the wavelength range of 200-420 nm are favorable properties for the application as lighting-emitting-diode conversion phosphor.