The paper is a survey of experimental and theoretical results on exciton states in crystals of xenon, krypton, argon and neon. The absorption and luminescence spectra of the crystals and the band structure of electron and exciton states are analysed. Some features of the exciton-phonon interaction in pure and doped crystals are discussed. In contrast with other types of molecular crystal, those of rare gases can simultaneously support free and localized excitons. All features of the exciton spectra, in particular the hydrogen-like series of light absorption, the rich pattern of luminescence and the absorption and emission bands due to impurity centres, have been given a natural explanation in terms of the intermediate-radius exciton strongly bonded to the crystal lattice. These investigations of excitons in atomic cryocrystals have revealed a number of new effects and extended our knowledge of the cooperative excitation states of dielectrics.

Excitons in rare-gas crystals

An 800 l liquid xenon scintillation γ -ray detector is being developed for the MEG experiment which will search for μ + → e + γ  decay at the Paul Scherrer Institut Absorption of scintillation light of xenon by impurities might possibly limit the performance of such a detector We used a 100 l prototype with an active volume of 372 × 372 × 496 mm 3 to study the scintillation light absorption We have developed a method to evaluate the light absorption, separately from elastic scattering of light, by measuring cosmic rays and α sources By using a suitable purification technique, an absorption length longer than 100 cm has been achieved The effects of the light absorption on the energy resolution are estimated by Monte Carlo simulation

Absorption of scintillation light in a 100 l liquid xenon γ-ray detector and expected detector performance

A review of the status of research towards achieving lasing action in the vacuum ultraviolet and soft X-ray spectral regions is presented. An analysis of the general problems likely to be encountered is accompanied by numerical results for those approaches currently considered promising. Progress on each approach is detailed and various possible methods of verifying the presence of gain with their relative merits are discussed. Research areas requiring Application of short-wavelength lasers also are given.

Review of short wavelength laser research

Vacuum ultraviolet absorption spectra of binary rare gas mixtures Xe/X (X=He, Ne, Ar, or Kr) and Kr/Y (Y=He, Ne, Ar, or Xe) near each of the first two resonance lines of Xe i and Kr i, respectively, have been photographed at high resolution by a 6.65 m spectrograph with a rare gas continuum as background source. The overall formation of spectral features near a resonance line is predominantly towards short wavelengths, and the degree to which discrete bands form near a resonance line generally increases with increasing atomic weight of X or Y. Partial interpretations of the absorption spectra are given in terms of transitions within the heteronuclear rare gas van der Waals molecule XeX or KrY, from the bound ground electronic state (Ω=0) to bound or free excited electronic states (Ω=0,1). Bound excited electronic states are found for KrXe near the first resonance levels of Xe i and Kr i, and for KrXe and ArXe near the second resonance level of Xe i.

Vacuum ultraviolet absorption spectra of binary rare gas mixtures and the properties of heteronuclear rare gas van der Waals molecules

A review of the status and properties of coherent sources of ultraviolet radiation is presented. This includes a wide range of developments concerning atomic and molecular systems useful for generating wavelengths below 4000 A, as well as progress in alternative methods of ultraviolet production. Particular emphasis is placed on recent advances in molecular bound-free systems whose operation is enhanced at high densities. It is believed that some of these systems may be scalable to sufficiently high-energy outputs to be useful in controlled fusion applications. A brief prognosis and discussion of future developments tending to the X-ray region are given.

O.V. Bogdankevitch

Papers

Luminescence of condensed Xe, Kr, Ar and their mixtures in vacuum region of spectrum under excitation by fast electrons