Potassium chloride crystals have been doped with ${\mathrm{Sm}}^{2+}$ ions to concentrations of 5×${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$, resulting in identifiable ${\mathrm{Sm}}^{2+}$ absorption spectra. Heating of the doped crystals in K vapor produces no visible change in the samples. Exposure to gamma irradiation at room temperature leads to a decrease in the ${\mathrm{Sm}}^{2+}$ absorption bands accompanied by an equivalent growth in the near infrared of a characteristic spectrum which can be explained in terms of electric dipole transitions between the $4f^{6}6s^1$ and $4f^{5}6s^2$ configurations of the ${\mathrm{Sm}}^{1+}$ ion. The conclusion that ${\mathrm{Sm}}^{2+}$ ions are reduced to ${\mathrm{Sm}}^{1+}$ by the capture of an electron is supported by the observation that the growth rate of the ${\mathrm{Sm}}^{1+}$ bands is equal to the decay rate of the ${\mathrm{Sm}}^{2+}$ bands. Magnetic susceptibility and electron paramagnetic resonance (EPR) observations are shown to be consistent with the reduction hypothesis.

• Received 2 March 1966

DOI:https://doi.org/10.1103/PhysRev.151.299