UV cathodoluminescence of crystalline α-quartz at low temperatures

Two luminescence bands in the UV range were detected in crystalline α-quartz under electron beam excitation (6kV, 3-5 μA). One band is situated at 5eV and could be observed in pure samples. Its intensity increases with cooling below 100K and undergoes saturation below 40K alongside a slow growth with the time of irradiation at 9K. The decay curve of the band at 5eV contains two components, a fast ( < 10ns) and a slow one in the range of 200 μs. The photoluminescence band at 5eV with a similar temperature dependence was found in previously neutron-irradiated crystalline α-quartz. Therefore, the band at 5eV was attributed to host material defects in both irradiation cases. The creation mechanism of such defects by electrons, the energy of which is lower than the threshold for a knock-out mechanism of defect creation, is discussed. Another band at 6eV, containing subbands in different samples, appears in the samples containing aluminum, lithium and sodium ions. This luminescence is ascribed to a tunnel radiative transition in an association of (alkali atom)⁰-[AlO₄]⁺ that is formed after the trapping of an electron and a hole by Li⁺ (or Na⁺) and AlO₄.