Identification of F+ centers in hafnia and zirconia nanopowders

• Undoped hafnia and zirconia nanopowders were prepared by solution combustion synthesis.
• Radiative decay of electronic excitations were investigated using luminescence methods.
• F+ centers emission bands were identified at 2.8 eV in hafnia and zirconia.
• Energy transfer to the defect centers occurs via electron–hole mechanism.
• Multiplication processes of electronic excitations were analyzed for zirconia.

Luminescence properties of undoped hafnia and zirconia nanopowders prepared by solution combustion synthesis were investigated under photo- and electron-beam excitation in 10–400 K temperature range. Along with the main luminescence band revealed in investigated materials at low temperatures at 4.2–4.3 eV and ascribed to the emission of self-trapped excitons, there are luminescence bands due to defects and impurities introduced during sample preparation. At room temperature the latter emissions dominate in the luminescence spectra as the intrinsic self-trapped exciton emission is quenched. Analysis of decay kinetics of defect centers allowed identification of F+ centers emission at 2.8 eV with lifetimes ∼3–6 ns in hafnia and zirconia under intra-center excitation.