Rare interactions of neutrinos with matter offer the path to understanding their properties as well as important astrophysical phenomena. Neutrinos are also emitted in large quantities from the nuclear fuel cycle, which has led to the emergence of applied antineutrino physics as a sub-discipline that seeks to make the use of neutrino detection in nuclear energy and security. Directly detecting dark matter and detecting MeV-scale neutrinos share many technological challenges, which has led to synergistic research in the communities working in those two areas. This talk will first discuss an emerging approach to detecting neutrinos with opaque scintillators. By constraining scintillation photons to a small volume and extracting them using wavelength-shifting fibers, interaction topology can be reconstructed with excellent spatial resolution. Originally conceived for reactor neutrino detection, opaque scintillators can relax the material doping constraints and be functionalized for various rare event detection problems where backgrounds must be strongly suppressed. The talk will then discuss our work in detecting low-energy nuclear recoils in germanium and noble elements that have implications on the detection sensitivity of dark matter and nuclear fuel cycle neutrinos.