Functionalization Aspects of Water Dispersible Upconversion Nanoparticles

Authored by: Markus Buchner , Verena Muhr , Sandy-Franziska Himmelstoß , Thomas Hirsch

Upconverting Nanomaterials

Print publication date:  October  2016
Online publication date:  October  2016

Print ISBN: 9781498707749
eBook ISBN: 9781315371535
Adobe ISBN:


 Download Chapter



Upconversion nanoparticles (UCNPs)/nanomaterials have the unique property to absorb near-infrared (NIR) light which leads to an anti-Stokes emission from the ultraviolet (UV) over the visible to the NIR range (Zhang 2014). The NIR light is absorbed by sensitizer ions (e.g., Yb3+ and Nd3+), and then transferred to so-called activator ions (e.g., Tm3+, Er3+, and Ho3+) via a nonradiative, resonant energy transfer process. The lanthanide ions are preferably embedded in host lattices with low phonon energy and similar ionic radii to reduce nonradiative deactivation processes (Haase and Schäfer 2011; Suyver et al. 2006; Wang and Liu 2009). Fluorides combine low phonon energies (~300–400 cm−1) with high chemical stability compared to other halide ions or oxide materials. The doping ratio of the sensitizer and activator ions is very critical, in order to generate highly fluorescent nanomaterials and to avoid self-quenching of the excited states. A NaYF4 hexagonal host lattice doped with Yb3+ and Er3+ ions and a simplified overview of the energy transfers inside the crystal is depicted in Figure 4.1. Figure 4.1 Hexagonal crystal lattice of NaYF<sub>4</sub> doped with 20% Yb ions and 2% Er ions. The Yb<sup>3+</sup> ions are excited at 980 nm (<sup>2</sup>F<sub>7/2</sub> → <sup>2</sup>F<sub>5/2</sub>) and transfer their energy to Er<sup>3+</sup>, which can then either emit from the <sup>2</sup>H<sub>11/2</sub> state (green emission) or the <sup>4</sup>F<sub>9/2</sub> state after internal relaxation (red emission).

Search for more...
Back to top

Use of cookies on this website

We are using cookies to provide statistics that help us give you the best experience of our site. You can find out more in our Privacy Policy. By continuing to use the site you are agreeing to our use of cookies.