Recombination luminescence in liquid argon and in liquid xenon

An electric-field effect on the luminescence of liquid argon and xenon excited by ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ internal-conversion electrons has been studied. A decrease in the luminescence was observed (67% at 10 kV/cm for liquid argon and 74% at 12.7 kV/cm for liquid xenon relative to the intensity without an applied field), and is explained by the escape of electrons and holes before recombination. This provides strong evidence for the existence of the recombination luminescence. Quantum efficiencies of recombination and self-trapped exciton luminescence are briefly considered.