Speaker
Description
Zirconia-based materials are widely used in optical, energy-related, and functional ceramic applications owing to their excellent mechanical, thermal, dielectric, and chemical stability. Their properties can be tailored through stabilization with aliovalent dopants, including luminescent rare-earth (Eu, Yb, Gd) and transition-metal (Mn, Cu) ions. Such modifications affect phase composition, defect concentration, and local crystal structure, which in turn determine the optical response of the material. Due to their sensitivity to the host lattice, luminescent centers can serve as probes of structural transformations, defect formation, and energy-transfer processes in zirconia-based systems.
In this work, synchrotron vacuum ultraviolet (VUV) spectroscopy combined with structural characterization was applied to investigate two groups of zirconia-based materials. The first group consisted of Y-stabilized and rare-earth-doped ZrO2 ceramics, where the yttrium content was varied to control phase composition, while rare-earth ions served as luminescent probes of the local crystal environment. The second group included cubic zirconia stabilized with approximately 10 mol.% rare-earth oxides, in which dopant ions simultaneously acted as structural stabilizers and emitting centers.
Undoped and doped zirconia nanopowders and ceramics containing Y, Eu, Yb, Gd, Mn and Cu were synthesized by coprecipitation and impregnation methods and calcined at 400 °C. The obtained powders were compacted and sintered in the temperature range 600-1600 °C. Structural and microstructural characterization was performed using Raman spectroscopy, Fourier-transform infrared spectroscopy, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy.
Luminescence excitation and emission spectra were measured at the P66 beamline of PETRA III (DESY, Hamburg) in the 120-330 nm and 290-1100 nm spectral ranges, respectively. The analysis of recorded emission-excitation maps allowed separating intrinsic host-related emission from dopant-related luminescence and provided insight into the excitation pathways in zirconia-based materials.
The optical response was found to depend strongly on both phase composition and dopant incorporation. In Y- and rare-earth-codoped zirconia ceramics, changes in the relative fractions of monoclinic, tetragonal, and cubic phases significantly modified the intrinsic and dopant-related luminescence. Excitation-dependent measurements revealed rare-earth excitation through both host band-to-band absorption and charge-transfer states and enabled separation of intrinsic defect emission from impurity-related luminescence. Similar competition between defect- and impurity-related recombination channels was observed in Mn- and Cu-doped materials. These findings indicate the coexistence of multiple luminescence pathways involving intrinsic defects, oxygen vacancies, and impurity centers, with their relative contributions governed by crystal structure and dopant type.
The results demonstrate the potential of synchrotron VUV spectroscopy as a powerful tool for elucidating the relationships between crystal structure, defects, excitation mechanisms, and luminescent properties in zirconia-based materials.
Acknowledgements. The authors are thankful to DESY User Office for financial support from the NEPHEWS project funded by the HORIZON-Europe program (project IC-20251517-EC).