Effect of Ce3+ dopant ions on the shape and luminescence of YPO4:Eu3+ and YPO4:Tb3+ nanocrystals

Nanoparticles of YPO4:Eu3+, YPO4:Eu3+:Ce3+, YPO4:Tb3+, and YPO4:Ce3+:Tb3+ with different amount of Eu3+ or Tb3+ dopant ions were synthesized by a hydrothermal route. Particle structures and morphologies were investigated and it was found that the increase of Eu3+ or Tb3+ ions, and co-doping with Ce3+ ions resulted in a transition of the crystal structure from tetragonal to hexagonal phase. The phase transition and the morphology transformation should be ascribed to the change of the average radius of cation by doping Ce3+, or to the changing the amount of Eu3+ or Tb3+. The energy transfer from Ce3+ ions to Eu3+ and Tb3+ ions was tested by studying the photoluminescence lifetime of YPO4:Eu3+, YPO4:Eu3+:Ce3+, YPO4:Tb3+, and YPO4:Ce3+:Tb3+ nanoparticles, and their energy transfer results in the improvement of the luminescence intensity. A schematic diagram for the electronic transitions of the studied systems is presented.