RECONSTRUCTED ADIABATIC POTENTIAL-ENERGY SURFACES FOR SELF-TRAPPED EXCITONS IN BINARY OXIDES

Adiabatic potential energy surfaces (APESs) for self-trapped excitons (STEs) (incipient Frenkel pairs) in alpha-quartz and alpha-alumina are deduced from experimental temperature dependences of the decay constants for transient volume change, optical absorption and luminescence, associated with the lowest STE state, as induced by a electron pulse irradiation. APES profiles along some effective 'reactive coordinate' are obtained by processing the temperature data by means of the reaction rate method. The resulting profiles suggest that STEs and defect pairs (DPs) in alpha-quartz, each incorporating an interstitial oxygen (O(i-)) and a singly charged oxygen vacancy (E'1 centre), are likely to form as two energetically non-equivalent pseudo-Jahn-Teller distortions of the quasi-symmetry of the saddle-point configuration between STEs and DPs. The APES for alpha-alumina appears to be inherently different from that for alpha-quartz. Now the pseudo-Jahn-Teller conjecture is likely not to apply immediately, owing to a very small crossover splitting. Implications for the defect formation process in quartz will be discussed.