Quantum confinement effect on Gd2O3 clusters

The evolution of the gap of a nanoscaled insulator material, namely, Gd(2)O(3), has been observed by means of vacuum ultraviolet excitation spectra of a dopant (Eu(3+)). The nanoparticles have been synthesized by the low energy cluster beam deposition technique and grown afterward by different annealing steps. A gap shift towards the blue is observed, similar to what is observed in semiconductor nanoparticles. Despite the strong ionic character of the material, the evolution exhibits a behavior similar to covalent materials. The evolution of the gap for Gd(2)O(3) follows the same empiric rule that has been derived for semiconductors (ZnO, CuBr, Si, and CdS). It shows that, in spite of the strong ionic character of the material (0.9 on the scale of Phillips), the amount of covalency is important enough for creating a significant delocalization of the electron with regard to its hole.