Spectral Probing of Surface Luminescence of Cubic Lu2O3:Eu3+ Nanocrystals Synthesized by Hydrothermal Approach

Cubic Lu 2 O 3:Eu 3+ nanorods, nanosheets, and nanoparticles are synthesized by a hydrothermal approach by adjusting the pH values of the precursor solutions. The unique luminescence properties of the nanocrystals are presented by the appearances of a long tail at the long-wavelength side of the charge transfer band (CTB), a novel 7 F 0 − 5 D 0 broad line, and the enhanced 624 nm emission line. The observed phenomena are more obvious with decreasing sample size in the order of nanorods > nanosheets > nanoparticles. Based on the experimental results of the thermal diffusion processes of Eu 3+ from the surface to the inside of Lu 2 O 3 particles, we conclude that the unique luminescence properties of the nanocrystals originate from the surface Eu 3+ . By the spectral decomposition, we obtain the excitation spectra of the interior Eu 3+ and the surface Eu 3+ of nanocrystals. In comparison with the bulk sample, the CTB of the interior Eu 3+ presents an obvious blue shift due to the size confinement effects, while that of the surface Eu 3+ shows a prominent red shift due to the distorted surface environments. The shorter lifetimes of the surface Eu 3+ compared to that of the interior Eu 3+ further indicate the distorted local environments on the surface of the nanocrystals. The shifts and the broadening of the CTB in Eu 3+ -doped nanocrystals can be well understood by the interior Eu 3+ and the surface Eu 3+ .