Luminescence and Luminescence Quenching of K2Bi(PO4)(MoO4):Eu3+ Phosphors with Efficiencies Close to Unity.

A very good light emitting diode (LED) phosphor must have strong absorption, high quantum efficiency, high color purity, and high quenching temperature. Our synthesized K2Bi(PO4)(MoO4):Eu3+ phosphors possess all of the mentioned properties. The excitation of these phosphors with the near-UV or blue radiation results in a bright red luminescence dominated by the 5D0 → 7F2 transition at ∼615 nm. Color coordinates are very stable when changing Eu3+ concentration or temperature in the range of 77-500 K. Furthermore, samples doped with 50% and 75% Eu3+ showed quantum efficiencies close to 100% which is a huge benefit for practical application. Temperature dependent luminescence measurements showed that phosphor performance increases with increasing Eu3+ concentration. K2Eu(PO4)(MoO4) sample at 400 K lost only 20% of the initial intensity at 77 K and would lose half of the intensity only at 578 K. Besides, the ceramic disks with thicknesses of 0.33 and 0.89 mm were prepared from K2Eu(PO4)(MoO4) powder, and it turned out that they efficiently converted the radiation of 375 nm LED to the red light. The conversion of 400 nm LED radiation to the red light was not complete; thus, the light sources with various tints of purple color were obtained. The combination of ceramic disks with 455 nm LED yielded the light sources with tints of blue color due to the low absorption of ceramic disk in this spectral range. In addition, these phosphors possess a very unique emission spectra; thus, they could also be applied in luminescent security pigments.