Argon, krypton, and xenon excimer luminescence: From the dilute gas to the condensed phase

Abstract

For the first time, the evolution ofluminescence from rare gases was studied as a function of number density. Synchrotron radiation served as a light source for selective and pulsed excitation of the samples. The excitation spectra confirm previous results on perturbed Rydberg states and exciton appearance in dense media. In time-resolved emission spectra the peak energies and widths of the luminescence bands were followed. The energy separation between the fast and slow components is found to be density independent. A model proposed by Cheshnovsky et al. [Chern. Phys. Lett. 15, 475 (1972)] accounts for the change in peak width with temperature. Both lifetimes decrease with increasing density. The data extrapolate to 3.3 ± 0.1 ns (Ar); 3.4 ± 0.1 ns, 270 ± 5 ns (Kr); 4.5 ± 0.1 ns, 100 ± 5 ns (Xe) for the low density limit. For the solid at the triple point, we obtain 1.3 ± 0.1 ns, 82 ± 5 ns (Kr) and1.1 ± 0.1 ns, 18.5 ± 0.5 ns (Xe). Theories on density dependence oflifetimes give only a qualitative description of the experimental results.

Ion-beam excitation of liquid argon

“…For similar time scales the two effects could not be resolved. In excitation of LAr with synchrotron radiation which had just enough energy to populate only the progenitor state of the excimer singlet indeed a singlet life time of (1.65 ± 0.1) ns was found [46]. This could be the undisturbed life time of the singlet state, as in the experiments with synchrotron radiation the energy was too low to ionize argon atoms and produce free electrons.…”

“…In the gas phase this width is found to decrease with decreasing temperature [7,[45][46][47][48]. The energy level of the singlet lies thereby slightly higher by ∼75 meV [46] than the energy level of the triplet state, however, due to the width of the second excimer continuum the two transitions cannot be resolved spectroscopically.…”

“…This is supposed to be due to the spectral splitting of the emission spectrum of singlet and triplet decays. The former peak at 126.6 nm, the latter at 127.6 nm (calculated from the data shown in [46]). Therefore, the singlet component is more dominant at shorter wavelengths.…”

“…The direct transition from triplet states into the ground state is forbidden, and only mixing between 3 Σ + u and 1 Π u states through spin-orbit coupling [53] renders the decay possible. The intensity ratio of singlet and triplet light is found to be dependent on the type and energy of the incident particle [7,8,23,24,46,52,54]. The time constants for the singlet and triplet light are, however, very similar for different incident particles [23,24,52,54], indicating that the same species are emitting the scintillation light and demonstrate the absence of substantial nonradiative quenching [10].…”

“…4), which could be related to a different local heating. In the gas phase the width is known to be influenced by temperature [7,[45][46][47][48].…”