Microwave reaction of Ln(OAc)(3).xH(2)O, Ln = Gd, Eu; OAc = acetate) with and in the ionic liquid [C(4)mim][BF(4)] (C(4)mim = 1-butyl-3-methylimidazolium) allows the fast and efficient synthesis of small, uniform, oxygen-free lanthanide nanofluorides with excellent photophysical behaviour. For GdF(3) : Eu(3+) nanoparticles a quantum efficiency of up to 145% was determined.