Ultraviolet luminescence of CsI and CsCl excited by soft x-ray laser

We present the observation of solid material luminescence excited by soft x-ray laser. The 21.2 nm photons of the soft x-ray laser of the Laboratoire d'Utilisation des Lasers Intenses (Palaiseau, France) have been used to induce ultraviolet luminescence in CsCl and CsI. The laser supplied up to 6×10¹² photons in 80 ps. A single laser shot was sufficient to obtain luminescence spectra with very good resolution. In the case of CsI, the use of two illumination conditions, differing by a factor 150 in intensity, showed the collapse of luminescence efficiency for very strong illumination. The quenching effect is discussed in terms of the large increase of crystal excitation mean density, altering the usual process of luminescence centers production.