Intrinsic and impurity luminescence of rare earth ions doped KYF4 nanophosphors

The KYF4 nanopowders, non-doped and doped with Ce3+ or Tb3+, having well-crystallized, unaggregated, monodisperse (±15%) nanoparticles with the cubic (the size in the range from ∼15 to ∼30 nm) or hexagonal (from ∼30 to ∼50 nm) crystal structure have been successfully synthesized by microwave-hydrothermal treatment of as-precipitated gels. In KYF4 hexagonal nanopowders an intense STE-type luminescence at ∼4.4 eV was observed which is not quenched at room temperature. In contrast to single crystals or cubic nanopowders, in KYF4 hexagonal nanopowders doped with Ce3+ or Tb3+, a rather efficient energy transfer is observed from the host to Ce3+ or Tb3+ ions, respectively, because of overlapping the emission spectrum of STE-type luminescence and the spectrum of efficient absorption on 4f-5d transitions in Ce3+ or Tb3+. ► In KYF4 hexagonal nanopowder an intense self-trapped exciton luminescence is detected. ► This excitonic luminescence in KYF4 hexagonal nanopowders is not quenched at 300 K. ► Emission band of excitonic luminescence overlaps with Ce3+ and Tb3+ 4f-5d absorption. ► In hexagonal KYF4 nanopowders an efficient energy transfer to Ce3+ and Tb3+ was found.