Ne/Xe/NF3 mixtures were irradiated by a cold‐cathode e‐beam, and the fluorescence yields of the B and C states of XeF were measured as a function of neon pressure from 200 to 5300 Torr. At low neon pressures, the fluorescence yield of the B state corresponds to one photon emitted for each neon ion formed. As the neon pressure is increased the fluorescence yield of the B state decreases, but the ratio of the C emission to B emission approaches unity. If the C is formed through a channel which is independent of the B state, then the ultimate efficiency of the XeF laser is severely limited. However, analysis of the data with a XeF kinetics model indicates that the enhanced C emission results from two‐body quenching of the B state by neon. We conclude that the XeF laser performance has been limited by other processes, namely, incomplete vibrational relaxation and ground‐state bottlenecking.