Electron Capture byαandFCenters in KBr

Abstract

Photoconductivity measurements were made on KBr containing $\ensuremath{\alpha}$, $F$, and ${F}^{\ensuremath{'}}$ centers to determine the electron-trapping probability (probability per unit time that one defect per ${\mathrm{cm}}^{3}$ traps an electron) of the $F$ center and the $\ensuremath{\alpha}$ center or negative-ion vacancy. The electron-trapping probability of the $\ensuremath{\alpha}$ center increased from 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$ per sec at 118\ifmmode^\circ\else\textdegree\fi{}K to 6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{3}$ per sec at 24\ifmmode^\circ\else\textdegree\fi{}K. The electron-trapping probability of the $F$ center increased from 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$ per sec at 118\ifmmode^\circ\else\textdegree\fi{}K to 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{3}$ per sec at 24\ifmmode^\circ\else\textdegree\fi{}K. The initial capture of an electron by an $\ensuremath{\alpha}$ center results in the formation of an excited $F$ center. The binding energy of this excited state was found to be 0.130 eV, corresponding to the first excited state of the $F$ center. Electron capture by an $F$ center was interpreted as occurring through the formation of an excited ${F}^{\ensuremath{'}}$ center. The binding energy of this state was found to be between 0.04 and 0.08 eV.