Читать книгу A Course in Luminescence Measurements and Analyses for Radiation Dosimetry - Stephen W. S. McKeever - Страница 31

In addition to point defects, one can also add even more complex defects consisting of line dislocations (boundaries between slipped and un-slipped lattice planes), grain boundaries, angular misfits between lattice planes, planar dislocations (internal surfaces), nanoparticle formations, inclusions, and precipitates. Another obvious cause of the breakdown in the periodicity of a lattice is the presence of a surface. Crystals are not infinitely large and at a surface the lattice periodicity ends abruptly giving rise to broken bonds and bonds passivated by the possible presence of foreign atoms, resulting in large concentrations of localized levels at the surface. Clearly, powdered materials with small grain sizes and large surface-to-volume ratios are more likely to exhibit effects due to surface states than larger, bulk materials.