Nanocrystalline lanthanide tetraphosphates: Energy transfer processes in samples co-doped with Pr3+/Yb3+ and Tm3+/Yb3+

Photoluminescent properties of nanocrystalline powders of the LiLa(PO3)4 system co-doped with Pr3+/Yb3+ or Tm3+/Yb3+ ions were reported. The powders were synthesized by precipitation method and annealed at 450 °C. Two series of the samples were prepared with 1 mol% of praseodymium or thulium ions and with various ytterbium content (from 2% up to 16%). Both the up- and downconversion energy transfers were studied, in particular, the spectra and kinetics of photoluminescence under blue (into Pr3+ or Tm3+ ions, respectively) and NIR (into Yb3+ ions) excitations. The possible mechanisms of energy migration were discussed. Higher ytterbium concentration resulted in higher energy transfer efficiencies for both tetraphosphate systems.