The goal of this work has been to investigate the down converting properties of thin film lanthanide fluorides. Down conversion is the process of splitting one high energy photon into two or more photons of lower energies, and has a great potential in drastically increasing solar cell efficiency. This can be achieved through interaction between pairs of different lanthanide ions, which is the core topic of this thesis. Thin films of LnF3 (Ln= Y, Ce, Tb, Yb) have been deposited with the atomic layer deposition (ALD) technique, including nanostructuring of films for efficient energy transfer between ions. Three different types of cerium precursors for synthesis of trivalent cerium films using ALD have been investigated. Ce(FOD)3 (FOD = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) has successfully been used together with TiF4 to produce thin films of CeF3. This process exhibits a relatively slow growth rate of ca. 0.1-0.2 Å/cycle and in part CVD-characteristics. Cerium cyclopentadienyl, Ce(Cp)3, and cerium hexamethyldisilazide, Ce(HMDS)3, proved less suitable for formation of Ce3+ containing compounds. The binary and multicomponent nanostructured LnF3 films have been characterised using high quality photoluminescence and time-resolved photoluminescence measurements at the University of Utrecht, Netherlands. The films proved to be poorly to non-existing luminescent due to titanium impurities from the TiF4 precursor, causing an emission quenching charge transfer between Ti4+ and Ln3+ (Ln = Ce and Tb). Highly luminescent Tb-hybrid films were fully quenched when introducing Ti4+ impurities and the possibility of inter-terbium energy migration by adding thin TbF3 layers at the same time, while the films were still luminescent when only introducing energy migration. This has previously been shown for terbium in titanates, but not in a matrix where titanium constitutes only minor impurities. One series of nanostructures show Yb3+ emission upon UV-excitation indicating efficient energy transfer in the material. The emission is activated by annealing and there are indications that the emission intensity can be tuned by nanostructuring.