Optically probing the crystalline phases of MnF2 and ZnF2 utilizing Sm3+ defect ions

We describe recent studies of epitaxially grown fluoride thin films aimed at isolating distinct crystalline phases present in the films. The MnF2 and ZnF2 films were grown on silicon wafers with a CaF2 buffer layer. Using excitation photoluminescence measurements, we observed one magnon absorption line of antiferromagnetic MnF2 microcrystals in the films. By doping these fluoride materials with samarium ions during the growth process, an effective optical probe of the different crystal phases was realized. We present emission and excitation spectra of Sm3+ centers in the fluoride films which can be associated with the rutile or α-PbO2 crystal structures stabilized in these films. In the case of MnF2 films, the excitation measurements demonstrate effective energy transfer to the defect Sm3+ ions in both crystal phases. These results suggest the presence of excitonic states within the α-PbO2 structure of MnF2; a structure not observed in bulk crystals grown under standard conditions. Our results demonstrate the effective use of an impurity ion to probe the structural and dynamical properties of thin films.