Morphology-controllable synthesis of LaOF:Ln(3+) (Ln=Eu, Tb) crystals with multicolor luminescence properties.

In this paper, well defined LaOF crystals with multiform morphologies were first prepared via the urea-based precipitation method followed by a heat treatment. The morphologies of the LaOF samples, including nanospheres and nanorods, can be easily modulated by changing the fluorine sources. XRD, FT-IR, SEM, TEM, and emission spectra were used to characterize the prepared samples. Under ultraviolet excitation, the LaOF:Ln(3+) nanospheres display the characteristic f-f transitions of Ln(3+) (Ln=Eu, Tb) ions and give bright red, and green emissions, respectively. Furthermore, by codoping the Tb(3+) and Eu(3+) ions into LaOF host and varying the doping concentration of the Eu(3+) ions, multicolor tunable emissions have been obtained under the irradiation of 379nm. These results show this material may have potential applications in field-emission displays.

A novel synthetic route towards monodisperse LaOF:Ln³âº (Ln = Eu, Tb) hollow spheres with multicolor luminescence properties.

In this study, monodisperse and uniform LaOF hollow spheres were successfully synthesized through a novel facile synthetic route employing a La(OH)CO3 sphere as a sacrificial template followed by a subsequent calcination process. The structure, morphology, formation process, and luminescence properties were well investigated using various techniques. The possible formation mechanism of evolution from the La(OH)CO3 spheres to the LaCO3F precursor, and to the final LaOF hollow spheres can be attributed to the Kirkendall effect and the decomposition of the LaCO3F precursor. Under ultraviolet excitation, the LaOF:Ln(3+) (Ln = Eu,Tb) hollow spheres show their characteristic f-f emissions and exhibit red, green emissions, respectively. Moreover, by codoping the Tb(3+) and Eu(3+) ions into the LaOF host and tuning their relative concentration ratio, multicolor tunable emissions are obtained due to the efficient energy transfer from Tb(3+) to Eu(3+) at 378 nm excitation. This material may find potential application in color display fields.

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.