CHARGE-EXCHANGE PROCESSES BETWEEN IMPURITY IONS AND THE HOST CRYSTAL IN WIDE BAND-GAP CRYSTALS

The point of this article is to investigate under what conditions the sum of a donor transition of an impurity ion, M(n+) --> M((n+1)+) + e( CB), and an acceptor transition M((n+1)+) + e(VB) --> M(n+) is equal t o the band gap of the host. Our recent work on Ti3+, Ti4+ in aluminate host crystals provides the best of the few examples where both a dono r and an acceptor transition are known.