Abstract
Luminescence from binuclear complex salts of Cr3+ ion is investigated at low temperatures for the first time as to rhodo-chloride, rhodo-chloride-perchlorate, rhodo-perchlorate and basic rhodo-chloride. The spectral features are dependent on the nature of the bridging groups. In the emission spectra of hydroxo-bridging compounds several sharp lines are observed at around 6800Å within an energy range of about 120 cm−1, and these lines are followed by vibrational structure extending to 7200Å. In the oxo-bridging complex, the spectrum involves two broad bands besides the sharp lines. The sharp lines are interpreted as orginating from Cr3+ ion pair due to the transition corresponding to the R lines in ruby, while the broad band observed in the oxo-bridging compound as being due to the reverse transition of the U absorption band. A superexchange interaction of the Heisenberg type is shown to be responsible for the features of the pair spectra. The theoretical analysis is transferred to Part II. The superexchange interaction is also considered to play an important role for the formation of unusual plateaus observed in the temperature dependence curves of emission intensities.
