Luminescence andF′Formation Involving Spin-PolarizedFCenters in KCl

Abstract

The electronic processes following optical excitation of $F$ centers in KCl are drastically changed if the $F$ electrons are spin polarized by magnetic fields at low temperatures (1.7°K). As the spin-aligned configuration of the $F^{\prime }$ center is forbidden, two effects appear: (1) The $F\to F^{\prime }$ conversion by conduction electrons becomes suppressed, and (2) the radiationless de-excitation of excited $F$ centers (caused by electron tunneling into neighboring $F^{\prime }$ center states) becomes suppressed, producing increases of the $F$ luminescence up to a factor 4.