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.
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