The Line Absorption Spectrum of Gadolinium Ion in Crystals

Abstract

With a view to determining the dependence upon crystal symmetry and chemical composition of the energy levels in a solid, the absorption spectrum of Gd⁺⁺⁺ in a number of different synthetic crystals has been photographed at temperatures between 300° and 20°K. Using the external crystallographic symmetry as an indication of the probable degree of symmetry about the gadolinium ion in the lattice, it is established that the important factor in determining the splitting of the multiplets or the excited levels is the lattice symmetry and not the negative ion except insofar as the negative ion influences the crystal structure, for the spectra of monoclinic gadolinium chloride, bromide, sulfate and selenate are almost identical, but are very different from the spectra of the hexagonal formate, bromate and ethylsulfate. Gadolinium propionate and butyrate evidently have somewhat different internal symmetry from that of the other monoclinic crystals since their spectra resemble much more the spectrum of triclinic gadolinium acetate. The group of compounds including gadolinium trichloracetate, propionate, butyrate, isobutyrate and trichlorbutyrate is similar in that the spectra of all are weak, diffuse, and little resolved even at the temperature of liquid hydrogen. The presence or absence of water of crystallization affects the spectra only slightly. The positions of the multiplets, and the positions of the lines within the multiplets of anhydrous gadolinium formate are much the same as in the ethylsulfate and bromate enneahydrates. The phenomenon of highly discrete selective reflection in the ultraviolet region by three compounds has been observed. A discussion of the nature of the excited states of the gadolinium ion in crystals is presented.