Energy Barrier against Self-Trapping of the Hole in Silver Chloride

We report the first observation of an energy barrier in the transition of a metastable free hole to the self-trapped state. The lifetime of the free hole was monitored by using electron paramagnetic resonance to measure the competition between self-trapping and trapping at such substitutional ions as ${\mathrm{Cu}}^{+}$. Over the range 4.5 to 30 K, the lifetime against self-trapping decreases with increasing temperature, with an activation energy of 1.7 meV.