Optical transitions associated with γ -radiation-induced defects in crystalline α-quartz were investigated by photoluminescence excited by both pulsed synchrotron radiation and steady-state light. After a 10 MGy γ -dose we observed two emissions at 4.9 eV (ultraviolet band) and 2.7 eV (blue band) excitable in the range of the induced absorption band at 7.6 eV. These two luminescence bands show a different temperature dependence: the ultraviolet band becomes bright below 80 K; the blue band increases below 180 K, but drops down below 80 K. Both emissions decay in a timescale of a few ns under pulsed excitation, however the blue band could also be observed in slow recombination processes and it afterglows in about 100 s at the end of steady-state excitation. The origin of the observed luminescence bands and the comparison with optical features of oxygen-deficient centres in silica glass are discussed in the framework of different models proposed in the literature.
Host luminescence excitation spectra and reflection spectra of and crystals at low temperatures have been measured in the energy region of 4-30 eV using synchrotron radiation. High-efficiency host luminescence is connected to radiative decay of self-trapped cation excitons. It is shown that also in the region of excitation multiplication, e.g. if the excitation energy is larger than twice the band gap energy , and in the relaxation process of core excitons the radiative self-trapped cation excitons are formed. However, the recombination of hole and self-trapped electrons (band-band excitation) does not give rise to host luminescence.
The absorption, reflection and luminescence excitation spectra, as well as the X-ray excited stationary and thermostimulated luminescence spectra of BBO crystals have been measured over a wide spectral (4-30eV) and temperature (8-300K) range. The experimental data show that the formation of the absorption edge of the crystal is strongly affected by excitonic-type excitations.
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