Rare‐earth fluorides are a class of materials with considerable potential in optical applications. Fluoride lattices typically permit high coordination numbers for the hosted rare‐earth ions, and the high ionicity of the rare‐earth‐to‐fluorine bond leads to a wide bandgap and very low vibrational energies. These factors make rare‐earth fluorides very useful in optical applications employing vacuum ultraviolet and near‐infrared excitation. The preparation of nanometer‐sized particles has opened the door for new properties and devices if the performance of their macroscopic counterparts can be conserved in the nanometer regime. However, at small particle sizes, defect surface states and adhering water reduce the optical efficiency. These shortcomings can be reduced by applying protective shells around the luminescent cores, which can also be involved in the luminescent process.

Transparent luminescent nanocomposites were obtained using the bulk polymerization of transparent dispersions containing manganese-doped ZnS nanoparticles with a crystallite size of 2 nm in a mixture of methyl methacrylate and acrylic acid. The effective diameter in the monomer dispersions is 22 nm as determined using dynamic light scattering and depends on the composition of the continuous phase but is significantly higher than the primary crystallite size of the ZnS:Mn nanoparticles initially obtained from the precipitation reaction. The dispersions are stable up to 8 months. Deprotonated carboxylate groups are detected in IR spectra (1547, 1437 cm-1) of particles isolated from a stable dispersion indicating the presence of surface-bound acrylate molecules. Thermal bulk polymerization of the entire dispersions is suitable for production of luminescent acrylic glasses with an emission maximum at 590 nm (330 nm excitation) and a quantum yield of 29.8%. Ultramicrotome cuts of the nanocomposites with a thickness of 50−100 nm were prepared for transmission electron microscopic investigations. In the micrographs, a low degree of agglomeration is observed and the agglomerate diameter is below 20 nm. In the nanocomposites, light scattering and turbidity is minimized due to the small particle size and high degree of dispersion, resulting in highly transparent acrylic glasses with a transmittance as high as 87% (600 nm).

Review: Non‐conventional phosphor host materials such as cryptands (see Figure) or zeolites now offer potential alternatives to the traditional inorganic solid‐state materials which find applications in e.g. fluorescent lamps, T.V. sets, or X‐ray detectors. Recent efforts to further optimize conventional materials are reviewed and a forward look is taken at the new‐generation materials which could further extend the physical limits of luminescence.