EXPERIMENTAL-STUDY OF THE EXCITATION THRESHOLD OF FAST INTRINSIC LUMINESCENCE OF CSI

A type of intrinsic luminescence in crystals has been revealed. The ex citation threshold of well-known fast intrinsic luminescence of CsI (3 00 nm band) has been obtained from the excitation spectrum measured in the photon-energy range 5-125 eV at 300 K using synchrotron radiation . The excitation starts from an energy of about 20 eV and exponentiall y increases up to the 4d I-ionization energy (approximately 50 eV). Su ch high-energy broad threshold is not typical for any conventional mec hanisms of luminescence excitation. We attribute this type of luminesc ence to the emission center, which is created by the interaction of se veral elementary excitations produced in the process of relaxation of a primary excitation. The possible role of 4d I- core levels is discus sed. The nanosecond decay kinetics of this luminescence is nonexponent ial for all energies of excitation.