Facile preparation of quantum cutting hexagonal NaGdF4:Eu3+ nanoparticles from ionic liquids

Inorganic fluorides doped with lanthanide ions provide as photonic materials some distinct advantages compared to other materials because of their outstanding properties such as very low phonon frequencies, high refractive index, high thermal stability and sometimes tunable crystal phases and related photophysical properties such as long lifetimes of their excited states and high luminescence quantum efficiencies. Such properties are needed for example as photon-down conversion or quantum-cutting phosphors for improved compact fluorescent lamps or solar cells. In our present study, we have prepared Eu3+ doped and coated sodium gadolinium fluoride nanocrystals using ionic liquids (ILs) which have been recognised as 'green' solvents or 'designer solvents'. IL assisted solution based methods as well as hydrothermal methods are used to prepare crystal phase controlled Eu3+ doped sodium gadolinium fluoride nanocrystals. A high quantum efficiency (187%) close to the maximum theoretical limit of 200% is measured for the doped hexagonal sodium gadolinium fluoride nanocrystals at the German synchrotron facility (DESY, Hamburg) which promises its future uses as an efficient quantum cutting phosphor in lighting industry. Further research is going on. (author)