Synthesis and luminescent properties of CeO₂:Pr ⁴⁺,Eu³⁺ red pigments

Coloring and photoluminescent properties of Pr⁴⁺- and Eu ³⁺-codoped CeO₂ were investigated to produce red-colored and redluminescent phosphors. CeO₂:Pr⁴⁺,Eu³⁺ particles were attempted to be synthesized by employing two kinds of methods; a conventional solid-state reactionmethod and a newly developed precipitationmethod. In case of the solid-state reaction, it was found that red emissions from the Eu³⁺-doped CeO₂ sample were enhanced by codoping Pr⁴⁺ at a extremely low concentration. The codoped Pr ⁴⁺ ions also generated red coloring of the sample. However, the light absorption due to the Pr⁴⁺ ions became stronger at the higher doping level, thereby quenching the red emissions from the Eu³⁺ ions. In the precipitation method using aqueous Pr(CH₃COO)₃ · 2H₂O solutions containing urea, luminescence quenching of products could be suppressed even at the higher Pr⁴⁺-doping level, leading to the development of red-colored phosphor materials. This achievement was due to the inhomogeneous distribution of the coloring Pr⁴⁺ ions and the emitting Eu³⁺ ions in the CeO₂ particles.