Recombination mechanism of luminescence excitation of self-trapped excitons in BeO

Time-resolved spectra, polarization of the luminescence and transient optical absorption (TOA) induced by irradiation of beryllium oxide crystals with electron pulses have been studied. Exponential stages with decay time τ = 6.5 ms in luminescence bands at 4.0, 5.0 and 6.7 eV coinciding in spectral and polarized properties with the luminescence of two different types of self-trapped excitons (STE) have been found. Efficiency of formation of centers with decay time 6.5 ms appeared to be comparable with that of formation of triplet STE. The electron fluence increase does not change the exponential character and relaxation of TOA decaying with time 6.5 ms and results in a linear growth of optical density. These data are typical of monomolecular recombination processes. Similarity of TOA spectra of centers with decay time 6.5 ms with those of V-type hole centers and hole component of STE shows that the stage 6.5 ms is due to the recombination of cation Frenkel defects. The recombination of close spatially correlated Frenkel pairs Be ⁺ V ^- manifests itself in a form of exponential components with decay time 6.5 ms in the luminescence of two types of STE in BeO.