Crystal structure and optical properties of erbium- and neodymium-doped zirconia nanoparticles

We report the synthesis, characterization, and optical properties of high-temperature stable lanthanide-doped luminescent zirconia nanoparticles via a novel method using carbon black as template. Dopant concentrations were varied from 1 to 5% of Er³⁺or Nd³⁺and annealing temperatures were varied from 650 to 1100 °C. The effects of the dopant concentration on crystal structure and emission properties were evaluated using x-ray powder diffraction and fluorescence spectroscopy, respectively. The lanthanide cations were found to stabilize the tetragonal phase of zirconia over the monoclinic phase as dopant concentration was increased to 5%. Increasing the annealing temperature to 1100 °C had the opposite effect and was found to stabilize the monoclinic phase of zirconia. The luminescence intensity of the Nd-doped zirconia was enhanced by two orders of magnitude over the undoped or Er-doped zirconia. In all cases, the luminescence spectra revealed increasing intensity with increasing annealing temperature. Zirconia luminescence at near-infrared wavelengths is likely caused by oxygen vacancies. This work demonstrates that the spectral signatures of fluorescent zirconia nanoparticles can be modified with small lanthanide dopant concentration. These particles will have utility in fluorescent sensors and tags, as well as new in refractory materials.