Neutron powder diffraction will be used to determine hydrogen positions in deuteride fluorides and mixed valent ytterbium deuterides. Mixed deuteride fluorides with distorted perovskite-type structure are interesting candidates as luminescent hosts for divalent europium. Because the local environment for the optical transitions of europium is of importance, the distribution of deuterium and fluorine have to be determined. The mixed valent ytterbium deuterides YbDx (2.3 < x < 2.67) are only stable under high deuterium gas pressure after applying specific temperature protocols. Therefore an Inconel gas pressure cell will be used and neutron diffraction data collected in situ under up to 500 bar gas pressure.