Luminescence of alpha-Al2O3 and alpha-AlOOH natural mixtures

Natural mixtures of sapphire (alpha -Al2O3) and diaspore (alpha -AlOOH) sam ples from Goian (NW Spain) have been analysed by scanning electron microsco py, electron microprobe, spectral luminescent techniques (thermoluminescenc e, radioluminescence, cathodoluminescence) and inductively coupled atomic p lasma bulk analyses. Blue coloured areas could be attributed to chromophore elements (FeO = 0.278%, TiO2 = 0.023%) and the large photon emission peak observed at 700 ran with 80 ppm of Cr2O3. Additional smaller bands at 670 a nd 720 nm can be assigned to Ti4+ and FeO in the lattice. The coexistence o f two different types of luminescent behaviour in the lattice of this mater ial, such as a discrete electron trap distribution at lower temperature (ci rca 190 degreesC) and a continuous trap structure at higher temperature (ov er 250 degreesC) and their relationship with dehydroxylation and chromophor e oxidation are explored. (C) 2001 Elsevier Science Ltd. All rights reserve d.