Rare Earth fluorides are a class of materials with high potential in optical applications. On one hand, fluoride lattices allow high coordination numbers for the hosted Rare Earth ions, on the other hand, the high ionicity of the Rare Earth to fluorine bond leads to a wide band gap and very low vibrational energies. These two essential factors in particular contribute to their usability in optical applications based on vacuum ultraviolet (VUV) and near infrared (NIR) excitation. Keywords in this context are 'downconverters' (multiphotonemitters, e.g. YF3:Pr, LiGdF4:Eu ) and 'upconverters' (e.g. YF3:Yb,Er ) as well as NIR-emitters (e.g. LaF3:Nd ). Recent attempts to control the size of such particles down to the nano-scale, at the same time maintaining the performance of their macroscopic counterparts, indicate accessibility of hitherto unrealized optical properties and applications. The preparation and optical characteristics of such nanoparticles and their embedding in polymeric, glassy or porous matrices to enable the manufacture of transparent hybrid materials will be discussed.
 R.T. Wegh et al., J. Lum., 82, 93, 1999
 L.F. Johnson et al., Appl. Phys. Lett., 15, 48, 1969
 J.W. Stouwdam, et al., Nano Letters, 2, 733, 2002