Study of the effects of heat treatments in the paramagnetic centers of alkaline feldspars and their implications in the luminescence properties

The present work shows a detailed study of the effects of preheating in ESR signals of four alkaline feldspar samples. ESR results showed Fe 3+ , Al-O — Al, Ti 3+ and [Pb-Pb] 3+ centers, When the samples were gamma-irradiated, the concentration of the Fe centers deceased in all the samples, but the Al-O –Al center concentration increased after about 50 Gy while that of the Ti 3+ and [Pb-Pb] 3+ centres became almost constant. The effects of preheating were observed in samples previously irradiated with doses of 0.2 and 3 kGy after heating at 100, 200, 300 and 400 o C, respectively for 10 minutes. In the orthoclase sample FELW, the Fe signal remained almost constant up to 300 C and increased at 400 C, while that of the Al center decreased slowly between 100 and 300 o C, but increased at 400 o C. In the microcline sample FELG an increase of the Al coupled with [TiO4] centres was observed up to 300 o C, while a decrease occurred for higher temperatures. Fe 3+ center concentration increased up to 200 C and became nearly constant for higher temperatures. According to our results, even preheating at temperatures as low as 200 o C can change the concentration of Fe, Al and Ti centers in the sample; this fact can modify the luminescence response of the samples with the dose, because all these centers are associated with one or more emission spectra bands.