Radiative Transitions New Results

The field of inorganic electronic spectroscopy has been extensively reviewed (see, for example, ref 18). In view of the amount of research already performed, one might wonder whether new transitions or known transitions located at deviating spectral positions can still be found. That this is indeed the case will be illustrated in this section. The selection of topics is not complete, but dictated by the author s interest and experience. 

Infrared Emission from Transition-Metal Ions 

Gtldel and coworkers have reported during recent years many cases of (near)infrared emission from several transition-metal ions. This was only possible by the use of suitable detectors of radiation (e.g., a cooled germanium photodetector) and careful crystal synthesis. Here we mention some examples. 

Compositions CsMgi.xNixCla show emission at about 5000 cm (19). The emission band shows vibrational structure yielding an S value of about 2.5. From this value AQ is found to be 0.7 A, which gives Ar = 0.24 A for the change in the Ni-Cl distance. This emission is due to a transition from one of the crystal-field components of the first excited state T2g to the A2g ground state (3d , Oh notation). The lifetime of the excited state is 5.2 ms. The luminescence is quenched above 200 K. 

In the analogous bromide system S, AQ, and Ar are larger than in the chloride system the Stokes shift is also larger, but the quenching temperature of the luminescence is lower, in agreement with the arguments given in Section II,A. 

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