Optical properties of off-centred Cu+ ions in KMgF3 crystals

Optical absorption and magnetic circular dichroism (MCD) spectra of KMgF3 crystals with different concentrations of Cu+ ions have been studied in the temperature range 15-296 K. Absorption bands due to isolated Cu+ are observed at 27 000, 28 593, 31 250, 32 010 and 47 600 cm(-1), and their intensities are almost constant for variation of temperature. A vibronic fine structure is observed with a sharp line at 27 460 cm(-1) on the low energy tail of the 28 593 cm(-1) band. From the temperature behaviour of the absorptions and MCD spectra of the intense 28 593 and 32 010 cm(-1) bands, it is concluded that the first four bands arise from the (3d)(10) --> (3d)(9)(4s) transition of Cu+ occupying an off-centred position at the K+ site. By comparison with the d(10) --> d(9)s Cu+ absorption bands in CaF2 and NaF, it is suggested that the 28 593 and 32 010 cm(-1) bands are caused by the (1)A(1g) --> T-1(2g) and (1)A(1g) --> E-1(g) transitions, respectively. while the weak 27 000 and 31 250 cm(-1) bands are related to the triplet states T-3(2g) and E-3(g). The high-energy 47 600 cm(-1) band is proposed to be attributable to the (3d)(10) --> (3d)(9)(4p) transition.