Temperature-Dependent Phase Changes in Multicolored Er_<i>x</i>Yb_<i>y</i>Zr_{1–<i>x</i>–<i>y</i>}O₂/Eu_0.02Y_1.98O₃ Core/Shell Nanoparticles

Abstract

We combine forced hydrolysis and homogeneous precipitation to synthesize metal-oxide precursors with spherical core/shell morphology. The core consists of an amorphous ErxYbyZr1–x–yO2 precursor, and the shell consists of an amorphous Eu0.02Y1.98O3 precursor. Upon heating, the doped metal-oxide precursors undergo gradual irreversible phase changes toward their crystalline oxide phases. The crystalline ZrO2 phase of the core forms at a lower temperature than the crystalline Y2O3 phase of the shell. The Er3+, Yb3+, and Eu3+ dopants can be photoexcited at specific wavelengths to emit their characteristic visible emissions. Depending on the Er3+/Yb3+ dopant ratio, the Er3+ dopant emission appears green, red, or yellow-brown, whereas the Eu3+ dopant emission appears orange-red. The irreversible temperature-induced phase changes are correlated with changes in the optical spectra of these materials. These temperature-induced phase changes and the respective changes in the optical spectra are detectable even when the nanoparticles are heated for only 10 s.