Preparation and properties of Eu2+/Eu3+ co-activated Ca9Lu(PO4)7 phosphors for multichannel photoluminescence

A series of single-phase white light-emitting phosphors Ca9Lu(PO4)(7):xEu(2+/3+) (x = 0.01-0.2) were successfully synthesized by a general high-temperature solid-state reaction in a CO atmosphere. Their crystallization and optical properties were investigated using powder X-ray diffraction (XRD), photoluminescence excitation (PLE), emission spectroscopy (PL) and fluorescence decay. The photoluminescence properties indicate that the excitation band of the obtained phosphors is located in the range of 240 to 460 nm, which matches well with that of the n-UV chip. For the emission spectra, a broad emission band around 484 nm and several sharp peaks due to the 4f-5d electronic dipole-allowed transitions of Eu2+ and the 4f-4f transition of Eu3+ ions can be observed. The emission colors turn from blue-green to white and eventually to red by simply adjusting the valence mixing of Eu2+/Eu3+ ions. The crystallographic sites of Eu2+ and Eu3+ ions in the Ca9Lu(PO4)(7) host were investigated by site-selective excitation and emission spectroscopy in the D-5(0) -> F-7(0) region and showed that europium shares positions M1, M2, M3 and M5 with calcium. It is suggested that Eu2+/Eu3+ ions have four different crystallographic sites in the doped Ca9Lu(PO4)(7) host, namely Ca(1), Ca(2), Ca(3) and Ca(5). Finally, the thermal quenching of Ca9Lu(PO4)(7):xEu(2+/3+) was investigated. As a result, the single-phase Ca9Lu(PO4)(7):xEu(2+/3+) phosphor may serve as a potential phosphor for application in white light-emitting diodes.