Stress absorption spectra of V 3+ in α‐Al 2 O 3 : Jahn‐Teller effect in the 3 T 2 state

Study under stress of 3 T 2 state of the V 3+ ion in corundum (α‐Al 2 O 3 ) was performed at 77 K. Absorption spectra are made on 3 A 2 ( 3 T 1 )→ 3 T 2 zero‐phonon lines and on the 3 A 2 ( 3 T 1 ) → → 1 A 1 sharp line. Under uniaxial stress, the degeneracy of vibronic levels is removed: curves show the shifts and splittings of 3 A 2 → 3 T 1 and 3 A 2 → 1 A 1 transitions as a function of the applied pressure. The strain interaction with 3 T 2 state only is deduced. The stress spectra cannot be quantitatively explained without taking into account a large S 15 * local elastic compliance. The local deformation around the V 3+ ion is similar to this one around the Cr 3+ or Co 3+ ion. Studying the 3 A 2 → 3 T 2 band by the method of moments a coupling between the V 3+ ion and a breathing mode A 1 is found. Results of measurements cannot be interpreted by a Jahn‐Teller effect with only the pure tetragonal modes.