Broad‐band vacuum ultraviolet (VUV) fluorescence has been observed in Nd3+‐, Er3+‐, and Tm3+‐doped LaF3, YF3, LiYF4, and LuF3by electron‐beam and VUV excitation. The VUV excitation spectra indicate a large Stokes shift (≳5000 cm−1) and a high fluorescence quantum yield of 0.8. The threshold power for laser action in these crystals by optical pumping has been estimated. Using a molecular H2laser as a pumping source, a laser system which is tunable from 1650 to 2600 A˚ could be constructed.