Ionic liquids (ILs) in recent years have attracted considerable interest due to their exceptional features such as wide liquid range, excellent thermal stability, wide electrochemical window, and low vapor pressure. In between, ILs have gained significant impact on organic synthesis [1]. Aiming at nanoscale materials and advanced nanostructures, exploration towards a beneficial use of ILs has just begun [2].

Here, a microwave-assisted synthesis in ionic liquids is presented as a novel approach to functional nanomaterials. LaPO₄:RE (Ce, Tb, Eu) and In₂O₃:Sn (ITO) have been selected as examples to prove the effectiveness of the synthesis. As a result, non-agglomerated and redispersible particles, 10-15 nm (LaPO₄:RE) and 25-30 nm (In₂O₃:Sn) in diameter were realized. Since heating is performed via microwave irradiation, synthesis is very fast (10 s at 300 °C) and leading to highly crystalline and anhydrous oxide particles. While exploring the material properties, in case of LaPO₄:Ce,Tb (45 mol-%, 15 mol-%) quantum yields of 70 % (Tb-emission) and 90 % (Ce plus Tb emission) were determined [3,4]. With concern to In₂O₃:Sn (7 mol-%) subsequent to ink-jet printing and densification, transparent ITO layers, 500 nm in thickness were formed exhibiting a specific resistance of 6.8 x 10^-2 Ωcm. Neither a thermal nor a chemical post-treatment is required to realize these values. With the properties gained the nanocrystals exceed comparable materials realized by other liquid-based methods [5,6].

References

[1] P. Wasserscheid, T. Welton (Eds.), Ionic Liquids in Synthesis, Wiley-VCH, Weinheim 2002.

[2] M. Antonietti, D. Kuang, B. Smarsly, Y. Zhou, Angew. Chem. Int. Ed. 2004, 43, 4989.

[3] G. Bühler, C. Feldmann, Angew. Chem. Int. Ed. 2006, 45, 4864.

[4] G. Bühler, C. Feldmann, Patent Application, DE 10 2006 001 414.6.

[5] G. Bühler, C. Feldmann, D. Thölmann, Patent Application, DE 10 2006 011 754.9.

[6] G. Bühler, D. Thölmann, C. Feldmann, Adv. Mater. 2007, in press.

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1. Synthesis of luminescent YVO₄:Eu nanocrystals in ionic liquids.
2. Microwave-assisted Synthesis of CaWO₄ Nanocrystals in Ionic Liquids