Excitation of Pulsed Cathodoluminescence by Picosecond Beams of Runaway Electrons

When excited by beams of runaway electrons with a duration of 100 ps, the pulsed cathodoluminescence of alkali halide crystals, cerium-doped yttrium-aluminum garnet ceramics, and synthetic gems (ruby, sapphire and diamond) was studied. The runaway electron beams were generated in the cathode-anode gap filled with atmospheric pressure air and focused by a non-uniform magnetic field with an amplitude of B ≈ 0.6 T into an area with a diameter of 15 mm. A comparative analysis was carried out between the findings and pulsed cathodoluminescence parameters of the same samples excited by an electron beam with a duration of 2 ns and a current density of 130 A/cm2 generated in a vacuum diode. In the case of irradiation with the runaway electron beams, the formation of F-centers has not been observed in alkali halide crystals, that arises out of a reduced radiation impact on samples. Thus, the spectral information is not distorted. When excited by a picosecond runaway electron beam, the decay kinetics of the Ce3+ luminescence band in yttrium-aluminum garnet ceramics is described by an exponential function with a characteristic time of 100 ns. When the ceramics are irradiated with a nanosecond electron beam with a higher fluence, the kinetic curve has a more complex shape with an additional maximum in the microsecond range due to the appearance of an extra pumping mechanism for the cerium emissive level. The luminescence spectra and kinetic parameters of the synthetic gems are identical in both cases. The difference is manifested only in the emission intensity, which is much weaker when samples are exposed to irradiation with picosecond runaway electron beams.