Synthesis and optical characterization of Gd2O3:Eu nanocrystals: surface states and VUV excitation

This paper reports on the synthesis and characterization of Gd₂O₃:Eu³⁺ nanocrystals of different sizes. The particles have been synthesized by a sol-lyophilization process. This methods allows the synthesis of 7–100 nm diameter cubic-phase particles. The photoluminescence properties have been studied with different excitation from X-ray to VUV and visible wavelengths. Compared to the properties of the bulk materials, some important changes on the luminescence are observed. In particular some bands are strengthened when the size of the particles is diminished. We could therefore ascribe this bands to doping ions on a site close to the surface. Also a very low efficiency of excitation for small particles is observed when exciting with X-ray or high-energy VUV photons (i.e. when exciting the host matrix) compared to the efficiency obtained when exciting in the charge transfer band or in the doping ions related states.