KEu(PO): hydrothermal synthesis, crystal structure and photoluminescence properties.

An anhydrous orthophosphate, KEu(PO) (tripotassium pentaeuropium hexaphosphate), has been prepared by a high-temperature solid-state reaction combined with hydrothermal synthesis, and its crystal structure was determined by single-crystal X-ray diffraction analysis (SC-XRD). The results show that the compound crystallizes in the monoclinic space group C2/c and the structure features a three-dimensional framework of [Eu(PO)], with the tunnel filled by K ions. The IR spectrum, UV-Vis spectrum and luminescence properties of polycrystalline samples of KEu(PO), annealed at temperatures of 650, 700, 750, 800 and 850 °C, were investigated. Although with a full Eu concentration (9.96 × 10 ions cm), the self-activated phosphor KEu(PO) shows s strong luminescence emission intensity with a quantum yield of 37%. Under near-UV light excitation (393 nm), the series of samples shows the characteristic emissions of Eu ions in the visible region from 575 to 715 nm. The sample sintered at 800 °C gives the strongest emission and its lifetime sintered at 800 °C (1.88 ms) is also the longest of all.