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The present work shows a detailed study of the effects of preheating in ESR signals of four alkaline feldspar samples. ESR results showed Fe3+, Al-O−Al, Ti3+ and [Pb-Pb]3+ centers, When the samples were gamma-irradiated, the concentration of the Fe3+ centers deceased in all the samples, but the Al-O -Al center concentration increased after about 50 Gy while that of the Ti3+ 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 oC, respectively for 10 minutes. In the orthoclase sample FELW, the Fe3+ signal remained almost constant up to 300 oC and increased at 400 oC, while that of the Al center decreased slowly between 100 and 300 oC, but increased at 400 oC. In the microcline sample FELG an increase of the Al coupled with [TiO4] centres was observed up to 300 oC, while a decrease occurred for higher temperatures. Fe3+ center concentration increased up to 200 oC and became nearly constant for higher temperatures. According to our results, even preheating at temperatures as low as 200 oC 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.

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