Effects of phonon confinement on the luminescence dynamics of Eu3+ in Gd2O3 nanotubes

The effects of phonon confinement on the excited state dynamics of Eu3+ in Gd2O3 nanotubes are investigated. Anomalous thermalization appears due to elimination of low-energy phonon modes in this highly efficient nanophosphor of many potential applications. It is observed that in the low-temperature excitation spectrum hot bands with fine structures originate from the lowest sublevel of F-7(1) at 217 cm(-1) above the ground state. The intensity of the hot bands hardly changes below 50 K, but it increases and exhibits normal Boltzmann thermalization above 50 K. The fluorescence lifetime of D-5(0) (2.19 ms at 10 K) is found to be unusually longer than that of the bulk counterparts, indicating a small filling factor of 0.55 for the nanotubes. These luminescent properties are attributed to the morphology and to the lack of low-energy phonon modes in the nanotubes.