Defects in sodalite-group minerals determined from X-ray-induced luminescence |
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| Authors: | Adrian A Finch Henrik Friis Mufeed Maghrabi |
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| Institution: | 1.Department of Earth and Environmental Sciences,University of St Andrews,St Andrews,UK;2.Natural History Museum,University of Oslo,Oslo,Norway;3.Department of Physics,Hashemite University,Zarqa,Jordan |
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| Abstract: | The luminescence spectra of a suite of natural sodium framework silicates including four different sodalite variants and tugtupite have been collected during X-ray irradiation as a function of temperature between 20 and 673 K. The origin of the emission bands observed in these samples is attributed to F-centres (360 nm), paramagnetic oxygen defects (400 and 450 nm), S2 ? ions (620 nm) and tetrahedral Fe3+ (730 nm). Luminescence in the yellow (550 nm) is tentatively attributed to Mn2+, and red luminescence in Cr-rich pink sodalite is possibly from Cr3+ activation. Sudden reduction in luminescence intensities of emission centres was observed for all minerals in the 60–120 K range. Since it is common to all the sodalite-group minerals, we infer it is a feature of the aluminosilicate framework. Sodalite luminescence has responses from substitutions on the framework (e.g. paramagnetic oxygen defects, Fe3+) which give sodalite properties akin to other framework silicates such as feldspar and quartz. However, the presence of the sodalite cage containing anions (such as F-centres, S2 ? ions) imparts additional properties akin to alkali halides. The possibility of coupling between Fe3+ and S2 ? is discussed. The overall luminescence behaviour of sodalite group can be understood in terms of competition between these centre types. |
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