Highly bright multicolour emission through energy migration in core/shell nanotubes.

This paper describes a simple and environmentally-friendly approach that allowed for the facile synthesis of a gadolinium-based core/shell/shell nanotube structure with a set of lanthanide ions incorporated into separated layers. In addition, by the rational design of a core/shell structure we systematically investigated the luminescence properties of different lanthanide ions in NaGdF4 host, and efficient down-conversion emission can be realized through gadolinium sublattice-mediated energy migration. The Gd(3+) ions play an intermediate role in this process. By changing the doped lanthanide ions, we generated multicolour emissions from the luminescent Ln(3+) centers via energy transfer of Ce(3+)→Gd(3+)→Ln(3+) and Ce(3+)→Ln(3+) (Ln = Eu, Tb, Dy and Sm) in separated layers. Due to the strong absorption of ultraviolet (UV) irradiation by Ce(3+) ions, the luminescence efficiency could be enhanced after doping Ce(3+) ions in the shell. In NaGdF4:5% Eu(3+)@NaGdF4@NaGdF4:5% Ce(3+) core/shell/shell nanotubes, with increasing the NaGdF4 interlayer thickness, a gradual decrease in emission intensity was observed for the Eu(3+) activator.