Enhanced phase stability and photoluminescence of Eu3+ modified t-ZrO2 nanoparticles

Tetragonal (t) ZrO2 nanoparticles have been obtained by a partial Eu3+-> Zr4+ substitution, synthesized using a simple oxalate method at a moderate temperature of 650 degrees C in air. The Eu3+ additive, 2 mol% used according to the optimal photoluminescence (PL), gives small crystallites of the sample. On raising the temperature further, the average crystallite size D grows slowly from 16 nm to a value as big as 49 nm at 1200 degrees C. The Eu3+:t-ZrO2 nanoparticles have a wide PL spectrum at room temperature in the visible to near-IR regions (550-730 nm) in the D-5(0)-> F-7(J) (Eu3+), J=1-4, electronic transitions. The intensity of the D-5(0)-> F-7(4) group is as large as that of the characteristic D-5(0)-> F-7(2) group of the spectrum in the forced electric-dipole allowed transitions. The enhanced t-ZrO2 phase stability and wide PL can be attributed to the combined effects of an amorphous Eu3+-rich surface and part of the Eu3+ doping of ZrO2 of small crystallites.