Multiplication of electronic excitations in CaO and YAlO₃crystals with free and self-trapped excitons

Abstract

Using synchrotron radiation of 6-32 eV the reflection spectrum and excitation spectra for 5.7, 4.6 and 2.8 eV emissions have been measured for a freshly cleaved CaO crystal at LHeT. In CaO, indirect band-to-band transitions take place in the region of hv>or=6.4 eV. The excitation spectra for intrinsic emissions of 5.9 and 4.2 eV were measured in a YAlO3 crystal at LHeT as well. As in many other dielectrics the electron-hole mechanism of multiplication of electronic excitations connected with the creation of secondary electron-hole pairs by hot photoelectrons also occurs in CaO and YAlO3 crystals. The creation of secondary excitons by hot photoelectrons has been detected in YAlO3 for the first time. The excitonic mechanism of multiplication of electronic excitations has a high efficiency in crystals with self-trapping excitons of small radii.