Electron Capture byαandFCenters in KBr

Abstract

Photoconductivity measurements were made on KBr containing $\alpha$, $F$, and $F^{\prime }$ 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 $\alpha$ center or negative-ion vacancy. The electron-trapping probability of the $\alpha$ center increased from 3×${10}^{-7\mathrm{}}$ ${\mathrm{cm}}^3$ per sec at 118°K to 6×${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^3$ per sec at 24°K. The electron-trapping probability of the $F$ center increased from 3×${10}^{-7\mathrm{}}$ ${\mathrm{cm}}^3$ per sec at 118°K to 4×${10}^{-6\mathrm{}}$ ${\mathrm{cm}}^3$ per sec at 24°K. The initial capture of an electron by an $\alpha$ 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 $F^{\prime }$ center. The binding energy of this state was found to be between 0.04 and 0.08 eV.