Acceptor Bound Exciton States in High‐Purity CuCl

The magneto‐optical properties of high‐purity CuCl at 4.2 K show that the two lines ν½ (25665.2 cm −1 ) and ν   2 ′(25697.6 cm −1 ) are due to transitions to (or from) excitons bound to the same neutral acceptor, the two holes arising from the lowest Γ 8 valence band. They are attributed, respectively, to the J = 5/5 and J = 1/2 states of the (A 0 , X) complex. These results are explained by the importance of the electron—hole exchange interaction and by a dominant occurrence of the Γ 8 rather than the Γ 7 neutral acceptors. As a consequence, free holes should chiefly arise from the Γ 7 valence band. This is due to the particularly low value of the valence band spin—orbit splitting (Δ SO ≈ 600 cm −1 ), compared to the free‐exciton binding energy ( E X ≈ 1523 cm −1 ) or to the estimated Γ 7 acceptor ionization energy ( E X ≈ 17000 cm −1 ). These conclusions support the previous assignment of line ν 2 (25654 cm −1 ) to a transition between a free Γ 7 hole and a Γ 6 charged exciton X   2 + .