Effect of ionization density on the time dependence of luminescence from liquid argon and xenon

The time dependence of luminescence in liquid argon and xenon has been studied for electron, α-particle, and fission-fragment excitation. The lifetimes of low excited molecular states (¹Σᵤ⁺ and ³Σᵤ⁺) do not depend on the density of excited species while the intensity ratio of ¹Σᵤ⁺ to ³Σᵤ⁺ is found to be larger at higher deposited energy density. The lifetimes obtained for the ¹Σᵤ⁺ and ³Σᵤ⁺ states are 7.0 ±{} 1.0 nsec and 1.6 ±{} 0.1 {μ}sec, respectively, in liquid argon, and 4.3 ±{} 0.6 and 22.0 ±{} 2.0 nsec, respectively, in liquid xenon. The mechanism of quenching of luminescence at a high density of excited species in liquid argon and xenon is discussed.