Luminescence at 400 and 440 nm in sanidine feldspar from original and X-ray-induced defects

The blue luminescence of feldspar crystals with molecular composition Ab38Or60An2 and high-sanidine X-ray diffraction pattern from Miocene rhyolite ash tuffs of the Twin Falls Volcanic Field (Idaho, USA) has been studied by high sensitivity thermoluminescence (TL) up to 400 °C at 2.5 °C/s and radioluminescence (RL) at room temperature. The natural thermally stimulated blue luminescence is composed by a single emission at 400 nm at T>200 °C probably linked to defect centres at original chemical impurities. The 50 Gy X-ray-induced TL emission exhibits a very symmetric broad band centred at 440 nm and 200 °C, attributed to unstable radiation-induced defects. The RL spectrum displays these two signals which can be explained since irradiation induces charge carriers, and subsequent electron–hole recombinations, in addition to optically active defect centres. The 400 nm band seems to be useful for dose reconstruction purposes.