Electron Spin Resonance and Optical Absorption of Electron Excess Centers in KCl

The effect of various conditions of optical bleaching and thermal annealing on the electron spin resonance and optical absorption of additively colored KCl has been studied. With extended optical bleaching the resonance linewidth narrows and the resonance saturates less readily. The presence of $R$, $M$, $N$, or $R^{\prime }$ centers is unrelated to the dominant features of the changes in resonance behavior; the optical absorption associated with the magnetic centers appears to remain in the region of the $F$ band.