Luminescence of the FAcentre in CaO:Mg

Abstract
The polarisation dependence of the emission intensity of the FA 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 FA(Mg) centre. The intensities and excited-state lifetimes of the fluorescent components of the F and FA 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 3T1u level of the F centre into higher excited states and are then transferred to FA+ centres thus giving FA+ to FA conversion. FA emission proceeds via the 3A1 to 1Aa radiative transition. Several features of this behaviour suggest that the defects are not distributed randomly in these crystals.

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