Knowledge Bank

The low lying electronic levels of rare earth ions, produced by crystal field splitting of the degenerate groundstate, have been observed in the absorption spectra of some rare earth double nitrates, ethyl sulphates and oxides. In the spectral range $10-50cm-1$ at least one absorption occurs clear of obscuring lattice absorption bands. Use of coolded InSb phtoconductive detectors, together with a simple grating monochromator, allows a resolution of $0.1cm-1$ to be obtained. The spectra give accurate values for line positions, widths and strengths. Line positions agree with values obtained by optical, ESR, specific heat and susceptibility measurements. Theoretical estimates of absorption strengths for magnetic dipole transitions are in reasonable accord with the experimental values. The linewidths in concentrated compounds are somewhat greater than values predicted from previous spin lattice relaxation measurements. Samples made by diluting the paramagnetic ions in the lanthanum compounds show a concentration dependent linewidth indicating that ion-ion- interactions are important. Theoretical estimates indicate that the two most important factors determining linewidth are the direct spin-lattice relaxation and a non dipoler ion-ion interaction (either electric quadrupolar or virtual phonon). Present address of E. Ellis: University of York.