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.