Luminescence in nano-size Y2O3:Ce

Nano-size cerium-doped yttrium oxide was investigated with the aim of influencing host and activator-related electronic transitions by size reduction. Complete quenching of Ce3+ luminescence in micro- and single-crystalline forms of this system has been attributed earlier to ionization of the cerium 5d electron to the conduction band of yttrium oxide upon excitation of a single f-electron to 5d state of Ce3+. We have tested the hypothesis of removing this activator-host excited state resonance via changes in electronic structure of the system that are expected with reduced crystallite size. In addition to usually observed Y2O3 emission peaking around 330 nm for short-wavelength excitation, broad luminescence bands were detected for excitations in 350–550 nm range. This luminescence appears white to naked eye and displays properties commonly characteristic of trivalent cerium ions located at more than one crystallographic site: multiple broad emission and excitation bands with fast decay times. The presence of similar emissions in undoped nano-Y2O3 indicates their origin to be associated with lattice defects. The potential changes in the lattice and electronic structures upon size reduction are discussed.