Defect luminescence in Li₂O crystal under γ-ray irradiation

Abstract

Luminescence emitted under γ-ray irradiation in Li₂O single crystal has been measured at 77—298 K using a ⁶⁰Co source for the first time. Effects of annealing temperature (773 or 1073 K) and cooling rate (about 50 or 400 K/h) were studied.

The luminescence emission was observed at 5.5—2.5 eV. The luminescence spectrum at 298 K was found to consist of five emission bands. The peak energies, in eV, of the luminescent bands in Li₂O annealed at 773 K and cooled with a quenching rate of 50 K/h are: 4.70, 4.13, 3.72, 3.30 and 2.87. It is suggested that the 4.70 eV emission band corresponds to the luminescence of a self-trapped exciton. The luminescence emissions at 3.72, 3.30 and 2.87 eV were assigned to the F⁰, F⁺ and F₂ centers, respectively. The origin of the luminescence band at 4.13 eV could be related to intrinsic defect or impurity luminescence. The activation energy for the thermal excitation into a non-radiative decay channel was elucidated to be 380, 140 and 115 meV for the 4.70, 4.13 and 3.72 eV bands, respectively.

The emission yield of F⁺ centers was strongly affected by the condition of heat treatment before irradiation.

Key Words:

• Lithium oxide
• Defects
• Luminescence
• γ-rays