Upconversion nanoparticles can absorb two or more photons and emit light with a higher energy than that of the exciting light. These nanoparticles have many potential applications, including imaging, however upconversion systems mostly involve lanthanide-doped nanoparticles.
Hongjie Zhang, Changchun Institute of Applied Chemistry, China, Peng Zhang, Dalhousie University, Halifax, Nova Scotia, Canada, and Xiaogang Liu, National University of Singapore, and their teams developed upconversion systems that utilize the emission of transition metals. They developed core–shell nanoparticles with Yb3+, Tm3+, and Gd3+ ions in the core, and Gd3+ and Mn2+ ions in the shell. A five-photon upconversion process results in population of the 1I6 state of Tm3+, and energy transfer proceeds via the 6P7/2 state of Gd3+ to the Mn2+ ions.
The researchers found that the color of the nanoparticle emission could be tuned by changing the power of the laser excitation. They confirmed that the emission occurred from the Mn2+ ions by measuring the emission with various core and shell compositions, as well as with an inert shell over the nanoparticles. The luminescence was quenched by hydrogen peroxide and thus the system can be used as a sensing platform.
The work shows that upconversion can take place at room temperature in transition-metal-doped host lattices comprising lanthanide tetrafluorides.
- Energy Migration Upconversion in Manganese(II)-Doped Nanoparticles,
Xiyan Li, Xiaowang Liu, Daniel M. Chevrier, Xian Qin, Xiaoji Xie, Shuyan Song, Hongjie Zhang, Peng Zhang, Xiaogang Liu,
Angew. Chem. Int. Ed. 2015.