Paramagnetic studies at 9375 Mc have been made on 32 inorganic phosphors containing paramagnetic activators. The sample is contained in a transmission cavity and the spectrum is obtained by a sweeping technique that yields the derivative of the absorption curve. Less than ${10}^{-11\mathrm{}}$ mole of ${\mathrm{Mn}}^{++}$ may be detected in cubic host crystals. The specimen in the cavity may be illuminated by ultraviolet light for observations on changes in its spectrum under these conditions, but, when illuminated, the changes observed may be attributed largely to photoconduction. The phosphors containing ${\mathrm{Mn}}^{++}$ as an activator under no illumination yield a variety of spectra. Seven of these phosphors display a single absorption line 750 to 1000 gauss wide, while four phosphors with different host crystals but all having cubic symmetry display line spectra consisting of six lines seven gauss wide but with spacings between members of from 68 to 88 gauss depending on the host crystal. Finally, two phosphors display 30-line spectra which arise because the crystal field and the applied field together serve to remove both the $I$ and $S$ degeneracy, whereas for cubic crystals only the $I$ degeneracy is removed.

• Received 7 July 1952

DOI:https://doi.org/10.1103/PhysRev.88.714