Diode-pumped cw lasers operating between 2 and 3 µm in the heavy rare-earth activator ions are reviewed. In Ho,Tm:YAG we demonstrated high efficiency using Tm as the sensitizer ion, which absorbed the pump radiation. This is followed by a cross-relaxation process, which allows two excited Tm ions to be produced from one absorbed photon. There is rapid energy migration among the Tm ions, followed by energy transfer to the Ho ion. The 2 pm laser action is to a level 460 cm-1 above the ground state. In Tm,Ho:YLF we demonstrated cw cascade laser emission at 2.31 and 2.08 µm. Above threshold for both transitions, two infrared photons are produced for each absorbed pump photon. The theoretical slope efficiency of this system is 72.3% for pumping at 0.791 µm. In Er:YLF, cw laser emission at 2.8 pm with a 10% slope efficiency was demonstrated. The laser transition is normally self-terminating, but an upconversion process, which depopulates the lower laser level and populates the upper laser level, allows this transition to operate in a cw mode.