Highly Efficient Multicolour Upconversion Emission in Transparent Colloids of Lanthanide‐Doped NaYF 4 Nanocrystals

Highly efficient photon upconversion in solution is demonstrated for the first time. Transparent colloidal solutions of Yb/Er and Yb/Tm doped NaYF4 nanocrystals show bright upconversion emission in the red, green, and blue spectral region by excitation around 1 μm with a laser of moderate power (see Figure). These new systems show a substantial improvement on the order of 108 compared to previously reported systems. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2004/c0772_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries…