Magnetic field effect on the photoluminescence of an Eu impurity during its aggregation in NaCl crystals

It is found that a magnetic field up to 20 T affects photoluminescence absorption spectra in NaCl:Eu crystals in the process of impurity aggregation into complexes. The spectral changes are irreversible and are observed after quenching the crystals at the early stages of the formation of small metastable complexes containing impurity-vacancy Eu$^{2+}$-V dipoles. Emporal correlations revealed between the occurrence of the magnetoplastic effect and a change in the optical properties of the crystals in a magnetic field.