Upconversion pumping has been demonstrated both experimentally and theoretically to be important in the 2.8‐&mgr;m4I11/2–4I13/2lasing transition in a CaF2(Er3+) system. A minimum pump threshold of only 2.8 J with a 1‐ms Xe lamp pulse has been achieved in CaF2rods containing 5 mol % of Er3+ions. A simple theory has been developed to show that upconversion pumping makes possible cw lasing between the4I11/2and4I13/2states even when the lifetime of the terminal4I13/2state is much longer than that of the upper4I11/2state. Semi‐cw lasing has been experimentally demonstrated by pumping with six ganged photographic flash bulbs fired in sequence, with each bulb having a duration of 15–20 ms. Lasing at 2.8 &mgr;m lasted for 80 ms, well beyond 10 and 20 ms lifetimes of the4I11/2and4I13/2states. The 2.8‐&mgr;m CaF2(Er3+) laser has also beenQswitched, using a 100‐nm thin graphite foil as a shutter.