Photoconductivity and charge trapping inα−Al2O3

Abstract

An electron trap which strongly affects the photoconductivity of colored $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3$ has been investigated from 10 to 300 K. The trap, which also causes the 260-K thermoluminescence peak and makes possible the interconversion of $F$ and $F^{+}$ centers by optical means, was studied in thermochemically-reduced samples as well as in samples which had been irradiated with high-energy electrons, reactor neutrons, or $\gamma$ rays. The activation energy for thermal release of the electron from the trap has been measured as 0.73±0.03 eV from the photoconductivity, thermoluminescence, and phosphorescence. The absorption band for optical release of the electron has been observed in the excitation spectrum of the photoconductivity near 5 eV, with a half-width of ∼0.6 eV. The possible identity of this and other traps is discussed.