EPR study of Fe3+ and Mn2+ doped amorphous and crystalline aluminum borates

Amorphous and crystalline aluminum berates prepared by sol-gel method doped with iron and manganese were studied by electron paramagnetic resonance in order to determine the matrix effects on Fe3+ and Mn2+ environments during their consolidation by heat treatment up to 860 degrees C. In amorphous ma trices, after heat treatments up to 600 degrees C, the Fe3+ environment is almost unaffected but the vicinity of Mn2+ ions is relatively strongly diso rdered. In partial crystalline alumina and aluminum berate samples, obtaine d after heat treatments applied at 860 degrees C, the Fe3+ sites are subjec ted to completely different crystalline fields, as regards intensity and sy mmetry. If in crystalline alumina we have both sites typical for alpha and gamma phases in crystalline aluminum berate, the well-known spectrum of Fe3 + in disordered systems seems to be solved, suggesting more than one well-d efined site. In the case of manganese-doped samples, only a diminishing of hyperfine resolution with increasing heat treatment temperature is observed as a result of environment distortion by improvement of alumina berate sam ple crystallinity.