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The main aim of the present project is the comparative investigation of peculiarities in the relaxation of electronic excitations in wide-gap fluorides and oxides under one- and multiphoton excitation using VUV-XUV radiation generated by conventional lasers and a free electron laser as well as by synchrotrons. Multiphoton spectroscopy in VUV (8-12 eV) is a novel research method of wide-gap insulators. Due to the different selection rules the non-linear spectroscopy provide acess to the excited states not reachable by one-photon method. Application of both excitation regimes allows to clarify the role of excitations of different parity in relaxation, migration, energy transfer, self-trapping as well as radiative and non-radiative decay with defect formation in fluorides and oxides. Practical importance of the project is related to the separation bulk and surface degradation effects of optical materials (CaF2, LiCaAlF6, etc.) used in VUV by enhanced bulk sensitivity of multiphoton techniques.The VUV free electron laser is a unique light source providing extreme intensities applicable in studies of excitation density effects on various processes occurring in insulators. So far luminescense studies in VUV have been mostly performed in a linear regime under weak or moderate excitation densities. The main goal is to investigate interaction of intense FEL radiation with various wide-gap insulators using time and energy resolved luminescence spectroscopy. The project will focus on the radiative and non-radiative decay of electronic excitations under high density excitation, mutual interaction of spatially close excitatitions and its influence on luminescence (their luminescence yield and kinetic properties), and possible non-linear effects (e.g. multiphoton excitation of cross-luminescence). Also the influence of excitation density and radiation damage on the performance of scintillators based on intrinsic (PbWO4) and activator emissions (various Ce doped materials) will be studied. |