An embedded cluster model is used to describe electronic structure of Cu + ion in NaF host. Transition energies and oscillator strengths are calculated for the 3d 10 →3d 9 4s 1 Cu + ligand field transitions. These are forbidden by dipole selection rules, which can, though, be broken by vibronic coupling. The basic model consists of a [CuF 6 ] 5− cluster surrounded by total ion potentials representing second, third and fourth neighbors to the central Cu + . The resulting structure is placed inside a cube of point charges to take long distance Coulomb interactions into account. Variations of this basic model needed especially to the calculation of transition energy. The oscillator strengths are calculated by the direct vibronic coupling method we have previously proposed. The effect of temperature on the value of the oscillator strength is calculated for the first time as well as their absolute value. Results are in good agreement with available experiment.