| Popis: |
Oxysulfide powders of yttrium, gadolinium, terbium and lanthanum display distinctive colors when they are either heavily ball-milled or pressed in a steel die. These colors are due to optical absorption bands in the visible region, peak positions of which obey an empirical rule like the Mollowo-Ivey relation of color centers in alkali halides. The c-axis shrinks in the colored samples. The colors are bleached and the cell constants are restored to the original values by heat treatment up to 450°C. Some distortions, however, still remain in the annealed samples. |
