abstract
Photoluminescent lanthanopolyoxotungstate core/shell nanoparticles are prepared by the encapsulation of lanthanide-containing polyoxometalates (POMs) with amorphous silica shells. The preparation of morphological well-defined core/shell nanoparticles is achieved by the hydrolysis of tetraethoxysilane in the presence of POMs using a reverse microemulsion method. The POMs used are decatungstolanthanoates of [Ln(W(5)O(18))(2)](9-) type (Ln(III) = Eu, Gd and Tb). Photoluminescence studies show that there is efficient emission from the POM located inside the SiO(2) shells, through excitation paths that involve O --> Eu/Tb and O --> W ligand-to-metal charge transfer. It is also shown that the excitation of the POM containing europium(III) may be tuned towards longer wavelengths via an antenna effect, by coordination of an organic ligand such as 3-hydroxypicolinate. The POM/SiO(2) nanoparticles form stable suspensions in aqueous solution having the advantage of POM stabilization inside the core and the possibility of further surface grafting of chemical moieties via well known derivatization procedures for silica surfaces. These features together with the possibility of tuning the excitation wavelength by modifying the coordination sphere in the lanthanopolyoxometalate, make this strategy promising to develop a new class of optical bio-tags composed of silica nanobeads with multi-wavelength photoluminescent lanthanopolyoxometalate cores.
keywords
3-HYDROXYPICOLINIC ACID; FLUORESCENT NANOPARTICLES; LANTHANIDE COMPOUNDS; SHELL NANOSPHERES; ENERGY-TRANSFER; QUANTUM DOTS; COMPLEXES; LUMINESCENT; POLYOXOMETALATE; ANION
subject category
Chemistry; Materials Science
authors
Granadeiro, CM; Ferreira, RAS; Soares-Santos, PCR; Carlos, LD; Trindade, T; Nogueira, HIS
our authors
Carlos Miguel Cardeal Enes Granadeiro
Post-Doc Fellowship
Helena Isabel Seguro Nogueira
Assistant Professor with Aggregation
Luís Carlos
Full professor
Maria Rute de Amorim e Sá Ferreira André
Full professor
Paula Cristina Ramos Soares e Santos
Laboratory Officer
Tito Trindade
Full professoracknowledgements
The authors thank Fundacao para a Ciencia e a Tecnologia (Portugal) for funding under the POCI 2010 and PTDC programs and FEDER (POCI/QUI/58887/2004 and PTDC/QUI/67712/2006), and for post graduation grants to CMG (SFRH/BD/30137/2006) and PCRSS (SFRH/BPD/14954/2004). We thank Dr Marc Willinger and the RNME (National Electronic Microscopy Network, Portugal) for HRTEM images.