Recombination luminescence and energy transfer in ionic crystals at XUV excitation by synchrotron radiation

The relative quantum yield spectra of recombination luminescence for MgO, α‐Al 2 O 3 , SiO 3 , and several alkali halide crystals are measured by synchrotron radiation in the photon energy interval 50 to 250 eV. The main feature of the spectra of oxides is a suppression of the volume luminescence due to surface losses of electrons and holes. For alkali halides surface as well as volume recombination luminescence take place. The more intensive the surface luminescence is the larger the absorption coefficient for exciting photons. The quantum yield spectra may be interpreted quantitatively on the basis of the hot carrier diffusion theory, the diffusion lengths being 2200 Å for MgO, 1500 Å for α‐Al 2 O 3 , and 300 Å for SiO 2 .