The nature of the X-ray-induced luminescence and the hole centres in CsI:Tl studied by optically detected electron paramagnetic resonance

Abstract

In the X-ray-induced luminescence band peaking at 560 nm we have detected the electron paramagnetic resonance (EPR) spectrum using optical detection (ODEPR) Of VK centres, which have their molecular axes perpendicular to the magnetic field, an EPR was only detected as a microwave-induced change in the magnetic circular polarization of the emission, and not as an emission intensity change. No parallel centres were seen, nor any trapped electron centre. The observations are explained as a recombination luminescence of a kind of Tl-bound exciton. Furthermore, the ODEPR via the magnetic circular dichroism of the absorption of VKA centres generated by X-irradiation at 4.2 K and trapped near Tl+ and near Na+ were measured. These centres are room-temperature stable for a few minutes and responsible for afterglow effects when using CsI:Tl, Na as X-ray-scintillator crystals.