Light absorption in mono- And polycrystalline YAG:Nd samples under pulsed electron irradiation

We studied the onset of induced optical absorption in mono- and polycrystalline Y₃Al₅O₁₂:Nd³⁺ samples upon irradiation by a nanosecond electron beam with electron energy of 250 keV and current density of 25 A/cm². We show that in such crystalline samples, the fast electrons produce induced absorption between 1 and 4.2 eV expressed as a superposition of six adjacent elementary lines. We found that the induced absorption is due to electron transitions from the valence band to a local level around an O⁻-hole center, while the initial-phase (10⁻⁷−10⁻⁴ s) relaxation of the induced absorption is determined by quadratic recombination of conduction-band electrons with the O⁻-hole centers. The higher density of structural defects in the polycrystalline sample than the monocrystalline sample increases the band-electron lifetime against capture by O⁻ centers.