Luminescence properties of a new greenish blue emitting phosphor Na5Ca4(PO4)4F:Eu2+

A novel greenish blue emitting phosphor, Na5Ca4(PO4)4F:Eu2+, was synthesized by a conventional solid-state reaction, and its phase formation was confirmed by using the X-ray powder diffraction (XRD) technique. The photoluminescence (PL) results showed that the phosphor could be efficiently excited by ultraviolet (UV) light at wavelength of 250–410 nm, and it exhibited bright greenish blue emission under 365 nm UV light. The emission spectrum showed a single broad band centered at 500 nm, corresponding to the 4f65d1 → 4f7 transition of Eu2+. Eu2+ concentration dependent PL properties in Na5Ca4(PO4)4F:xEu2+ indicated that there was a dipole–dipole interaction of Eu2+ ions. The critical energy-transfer distance was around 19.8 Å. Furthermore, this phosphor had good thermal stability and its thermal quenching activation energy was 0.45 eV. The measured quantum efficiency of Na5Ca4(PO4)4F:0.01Eu2+ phosphor under 365 nm excitation is 76%, which means that the present phosphor is promising in the white light emitting diodes (LEDs) phosphors.

► Na5Ca4(PO4)4F:Eu2+ phosphors have been studied.
► The emission spectrum showed a single broad band centered at 500 nm upon 365 nm UV light.
► Na5Ca4(PO4)4F:Eu2+ had a good thermal stability property and high quantum efficiency.