Optical and Photoelectrical Properties of β‐Rhombohedral Boron II. Photoeffects

Abstract β‐rhombohedral boron is characterized as infrared phosphor. Below 100 °C the optical absorption in the region between absorption edge and lattice vibrations as well as the electrical conductivity show a considerable rise during illumination with white light caused by two trapping levels of great density of states. At low temperatures both levels cannot be occupied simultaneously. Optical ionization spectra of charged traps (“photoabsorption”) give high activation energies confirmed by glow curves derived from the temperature dependence of photoabsorption. The recombination of trapped electrons and free holes does not take place directly but via the conduction band. Therefore it is considerably delayed especially at low temperatures because of the high ionization energies of the traps.