1 research outputs found
Luminescence and Luminescence Quenching of K<sub>2</sub>Bi(PO<sub>4</sub>)(MoO<sub>4</sub>):Eu<sup>3+</sup> 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 K<sub>2</sub>BiÂ(PO<sub>4</sub>)Â(MoO<sub>4</sub>):Eu<sup>3+</sup> 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 <sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>2</sub> transition at ∼615 nm.
Color coordinates are very stable when changing Eu<sup>3+</sup> concentration
or temperature in the range of 77–500 K. Furthermore, samples
doped with 50% and 75% Eu<sup>3+</sup> 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 Eu<sup>3+</sup> concentration. K<sub>2</sub>EuÂ(PO<sub>4</sub>)Â(MoO<sub>4</sub>) 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 K<sub>2</sub>EuÂ(PO<sub>4</sub>)Â(MoO<sub>4</sub>) 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