Journal of Electron Spectroscopy and Related Phenomena 101–103 (1999) 623–627 Hot luminescence of self-trapped excitons in Xe crystal under X-ray and two-photon laser excitation a, b a a a c * R. Kink ,V. Hizhnyakov , M. Selg , M. Kink , J. Maksimov , I. Martinson a Institute of Physics of Tartu University, Riia 142, Tartu EE2400, Estonia b ¨ Institute of Theoretical Physics of Tartu University, Tahe 4, Tartu EE2400, Estonia c ¨ University of Lund, Solvegatan 14, Lund S22363, Sweden Received 3 August 1998 Abstract A nonperturbative theory of anharmonic multiphonon decay of strong local vibration in crystal is developed, which ˚ predicts sharp acceleration of the process caused by cubic anharmonicity near characteristic amplitudes (typically A | 0.3 A), ˚ and abrupt switching-off of the processes caused by higher order anharmonicities at larger amplitudes (typically A | 1 A). * The first experimental observation of such a process is reported: strong acceleration of two-phonon decay of Xe 2 quasi-molecules is found in solid xenon. The experiment is based on X-ray and two-photon laser excitation (using an * excimer laser emitting at 193 and 248 nm) of hot luminescence of Xe .  1999 Elsevier Science B.V. All rights reserved. 2 Keywords: Multiphonon decay; Anharmonicity; VUV spectroscopy; Hot luminescence; Xenon 1. Introduction Standard perturbation theory [5] predicts a linear increase in the rate of two-phonon anharmonic decay of a local mode with energy E . For usual strength of According to Hawking [1,2], quantum fluctuations l anharmonic interaction and E * 30"v it corre- of a vacuum near the event horizon of a black hole l l sponds to the vibrational quantum per period or lead to appearance of emission, which enhances in more, which violates the condition of applicability of time (particles are created by pairs on different sides the theory. Recently a nonperturbative theory of of the event horizon). As a result, black hole ends anharmonic relaxation of strongly excited classical with a sharp explosion. Several authors (see, e.g., local mode has been worked out [3,4], which pre- [3,4] and references therein) have pointed out that dicts the explosion-like decay of the mode energy. In some aspects of the physics of black holes, including this work, a consistently quantum-mechanical de- the explosion-like behaviour of two-particle emis- scription of decay of a local mode anharmonically sion, can be modelled in condensed matter physics. interacting with phonons is given. The theory has been verified computationally and experimentally by studying the hot luminescence (HL) of self-trapped *Corresponding author. Fax: 1372-7-383-033. E-mail address: kink@fi.tartu.ee (R. Kink) excitons (STE) in Xe crystal at low temperatures. 0368-2048 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0368-2048(98)00345-4