ESR Studies of Covalency Effects between Cu 2+ and Chalcogen Ions in AgCl Crystals

After irradiation in AgCl crystals doped with Cu and Se or S, respectively, an ESR spectrum of a Cu 2+ ion is observed the octahedral chlorine environment of which is distorted by a Se 2− or S 2− ion. The centre has [100] tetragonal symmetry and a essentially |3 z 2 ‐ r 2 > ground state. The superhyperfine structure in AgCl: 77 Se, Cu indicates a strong interaction with one selenium nucleus. If σ‐bonding is assumed the magnitude of the covalency between the Cu 2+ and the Se 2− ion can be estimated: the hole spends about 20% of its time in a p z state of the Se 2− . From the existence of this covalent bonding in the paramagnetic complex follows that the spin‐orbit coupling is more reduced in [Cu 2+ Se 2− ] than in [Cu 2+ S 2− ].