The results of coordinated spectroscopic studies of the nature and properties of electronic excitations localized at regular and defect sites of the Be2SiO4 lattice are presented. The methods employed are electron-beam-excited pulsed absorption spectroscopy, pulsed cathodoluminescence, and low-temperature VUV spectroscopy with selective excitation by synchrotron radiation. The bands in luminescence spectra of Be2SiO4 at 2.70 and 3.15 eV are assigned to [AlO 4]5- and [SiO4]4- centers formed both in direct relaxation of electronic excitations at defect levels and through the formation of exciton-defect complexes. Disruptions of beryllium-oxygen bonds (short-lived defects in the form of beryllium vacancies V Be - ) are considered as initiating the formation of optically active centers with characteristic absorption bands in the range 1.5-4.0 eV. The intrinsic luminescence of the Be2SiO4 crystal at 3.6 and 4.1 eV is attributed to radiative decay of self-trapped excitons of two types. A mechanism of exciton self-trapping at the [SiO4] and [BeO 4] tetrahedral groups is proposed, which involves excitation transfer from a threefold-coordinated oxygen atom to neighboring silicon or beryllium atoms.
ASJC Scopus subject areas
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials