Superparamagnetic core-shell nanocomplexes doped with Yb3+: Er3+/Ho3+ rare-earths for upconversion fluorescence

Publication date: 15 September 2017
Source:Materials & Design, Volume 130
Author(s): Isabel Campos-Gonçalves, Benilde F.O. Costa, Rúben F. Santos, Luísa Durães
This work aims to obtain multifunctional nanocomplexes with a superparamagnetic core and an upconversion luminescent shell, by synthesizing superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with lanthanide ions. These materials may be used in numerous applications, e.g. in the biomedical and environmental fields. Three distinct nanocomplexes were synthesized: SPIONs@LaF3:Yb³⁺/Er³⁺, SPIONs@NaYF4:Yb³⁺/Er³⁺ and SPIONs@NaYF4:Yb³⁺/Ho³⁺. The first was obtained using the microemulsion and co-precipitation methods and the latter using the thermal decomposition method. A heat treatment was also applied to the SPIONs@LaF3:Yb³⁺/Er³⁺ nanocomplex. VSM revealed the superparamagnetic character of the nanocomplexes, and the saturation magnetization was 10.2emu·g⁻¹, 8.4emu·g⁻¹, 8.3emu·g⁻¹ and 14.0emu·g⁻¹ for SPIONs@LaF3:Yb³⁺/Er³⁺ without and with heat treatment, SPIONs@NaYF4:Yb³⁺/Er³⁺ and SPIONs@NaYF4:Yb³⁺/Ho³⁺ nanocomplexes, respectively. The upconversion process in these materials was confirmed by multiphoton microscopy. For SPIONs@NaYF4:Yb³⁺/Er³⁺, three peaks of emission were obtained, at 520nm, 540nm and 657nm, while for SPIONs@NaYF4:Yb³⁺/Ho³⁺ and SPIONs@LaF3:Yb³⁺/Er³⁺ samples only two peaks were observed, at 540nm and 647nm for the first, and at 540nm and 657nm for the latter. The results for the nanocomplex which uses Ho³⁺ ions as activators are very promising, since similar nanocomplexes are yet to be reported and good magnetic and luminescent properties were achieved.

Graphical abstract

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