Experimental evidence for spatial correlation between F and H centres formed by exciton decay at low temperatures in KBr

Optical detection of electron paramagnetic resonance of F-H-centre pairs created by low-temperature X-ray irradiation of KBr was performed via the magnetic circular dichroism of the optical absorption (MCDA) whereby cross-relaxation (CR) effects between the H and F centres were detected in the MCDA of the F centres. A quantitative analysis of the CR effects yielded direct experimental evidence that all F and H centres are spatially correlated after their low-temperature formation with a separation of four lattice sites along the (110) directions. A theoretical analysis of the CR result yields an estimate of the F-centre formation time of 2ps, in agreement with other experimental evidence, and also shows that the F-H separation obtained is the first stable F-H-centre pair configuration.