Luminescence of the FAcentre in CaO:Mg

Abstract

The polarisation dependence of the emission intensity of the F_A Centre in CaO:Mg has been investigated at 4K. This provides evidence that the long-wavelength side of the 460 nm absorption band found in CaO:Mg is the ¹A₁ to ¹E transition of the F_A(Mg) centre. The intensities and excited-state lifetimes of the fluorescent components of the F and F_A centres have been measured in the temperature range 4-250K. An interpretation of the results is given which suggests that electrons are thermally excited from the ³T_1u level of the F centre into higher excited states and are then transferred to F_A⁺ centres thus giving F_A⁺ to F_A conversion. F_A emission proceeds via the ³A₁ to ¹A_a radiative transition. Several features of this behaviour suggest that the defects are not distributed randomly in these crystals.