Field emission theory of dislocation-sensitized photo-stimulated exo-electron emission from coloured alkali halide crystals

Abstract

A new field emission theory of dislocation-sensitized photo-stimulated exo-electron emission (DSPEE) is proposed, which shows that the increase in the intensity of photo emission fromF-centres during plastic deformation is caused by the appearance of an electric field which draws excited electrons out of the deeper layer and, therefore, increases the number of electrons which reach the surface. The theory of DSPEE shows that the variation of DSPEE flux intensity should obey the following relation

$$\frac{{\Delta J_e \left( \varepsilon \right)}}{{J_e \left( o \right)}} = \left[ {\frac{{Y_s }}{{d_F }}\exp \left( {\frac{\chi }{{kT}}} \right) - 1} \right]$$

. The theory of DSPEE is able to explain several experimental observations like linear increase of DSPEE intensityJ _e with the strain at low deformation, occurrence of the saturation inJ _e at higher deformation, temperature dependence ofJ _e, linear dependence ofJ _e on the electric field strength, the order of the critical strain at which saturation occurs inJ _e, and the ratio of the PEE intensity of deformed and undeformed crystals. At lower values of the strain, some of the excited electrons are captured by surface traps, where the deformation generated electric field is not able to cause the exo-emission. At larger deformation (in between 2% and 3%) of the crystal, the deformation-generated electric field becomes sufficient to cause an additional exo-electron emission of the electrons trapped in surface traps, and therefore,t here appears a hump in theJ _e versusε curves of the crystals.