Equilibrium configuration of the self-trapped exciton in CaF2and SrF2

Abstract
The equilibrium configuration of the self-trapped exciton (STE) in CaF2 and SrF2 is calculated by minimising the total energy of the crystal containing an excited electron and a self-trapped hole. The electron is treated by the ion-size method and the lattice by pair potentials. It shows very clearly that the STE in fluorites is not equivalent to a Vk centre plus an electron, but is closer to a F+H pair. It is also shown that only one of the four possible configurations is directly realised after the self-trapped hole captures an electron. The interconversion between the different configurations is briefly discussed.

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