Intensity of d–s symmetry-forbidden electronic transition for Cu+ impurity in sodium chloride

Embedded cluster model is used to describe electronic structure of Cu+ ion in NaCl host. Transition energies and oscillator strengths are calculated for the 3d10 → 3d94s1 Cu+ ligand field transitions. These transitions are not allowed by dipole selection rules, which can, however, be broken through by vibronic coupling mechanism. A method is proposed to take into account the effect of vibronic coupling in the value of the oscillator strengths. Results for vertical transition energy are in much better agreement with experiments than previous calculations and optical oscillator strengths are reported for the first time.