Optical studies of self-trapped holes and excitons in beryllium oxide

Time-resolved spectra, decay kinetics, degree of polarization of the luminescence and transient optical absorption induced by irradiation of BeO with an electron, synchrotron and subsequent laser pulses have been studied. It is found that the two pairs of slowly and fastly decaying intrinsic luminescence bands at 6.7, 4.9 and 4.4 eV are associated with the two different types of the self-trapped excitons. The 1.7 eV transient optical absorption band and the ultra-violet absorption band at 3.6 eV are attributed to the electron and hole components of the self-trapped excitons, respectively. The transient optical absorption band with decay time of 6.5 ms is found to be due to the self-trapped holes. The models of self-trapped excitons and holes are discussed on the basis of the present experimental results.