Cathodoluminescence of nanostructured ceria in a high-voltage electron microscope

The cathodoluminescence (CL) of nanostructured CeO2 samples is studied under high-energy electron irradiation at room temperature and 106 K in a high-voltage electron microscope. The CL spectra of nanoparticles (32 nm in size) of CeO2 and a mesoporous CeO2 layer (9.4 nm in grain size) with a thickness of 1 μm on a silicon substrate were measured for 600 and 800 keV electrons. Very low light emission intensities were recorded for both samples. However, these noisy spectra reveal several CL bands after proper statistical smoothing by pixel binning and fitting with Gaussian profiles. A band centered at about 4.1 eV found for both samples is assigned to oxygen vacancies (F+ centers) like for the bulk coarse-grained CeO2 sintered samples and single crystal. Three additional bands between approximately 2 and 3 eV with similar intensities are assigned to Ce3+ ions as already found in bulk samples. For the mesoporous sample at 106 K, the F+-center band intensity increases with the electron energy in relation to the increase in the oxygen displacement cross section. The band intensities increase almost linearly with the beam current. However, narrower CL bandwidths are recorded for 800 keV electrons at 300 K with respect to bulk samples. A kinetic model is proposed to account for the decrease of the CL signal of nanocrystalline CeO2 with respect to bulk samples. These first results highlight the open possibilities of CL measurements on nanostructured samples for luminescence applications.