Defects in sodalite-group minerals determined from X-ray-induced luminescence

Abstract

of sodalite group can be understood in terms of competition between these centre types. Keywords X-ray excited optical luminescence (XEOL) • Thermoluminescence • Sodalite • Framework silicates • Luminescence 6 (O,S) 24 (SO 4 ,Cl) 1-2 ], lazurite [(Na,Ca) 8 Al 6 Si 6 O 24 (S,SO 4 , Cl) 1-2 ] and tugtupite [Na 8 Be 2 Al 2 Si 2 Si 6 O 24 Cl 2 ]. Some are prized as semi-precious stones (e.g. ultramarine and lapis lazuli) because the sodalite minerals show a range of colours including blue, pink, green, yellow, red and colourless. Synthetic analogues are finding applications as pigments (Schlaich et al. 2000) and efficient visible and infrared phosphors (Schipper et al. 1972; Lezhina et al. 2006). Some natural sodalites are tenebrescent, i.e. they change colour reversibly on exposure to daylight, a property which has inspired potential applications in, for example, security papers and smart coatings for blinds (Armstrong and Weller 2006). Despite being of such importance, there are relatively few published data relating to the luminescence of natural sodalites (e.g.

Luminescence and tenebrescence of natural sodalites: a chemical and structural study

“…The PL responses varied between yellow to purple and typically the colour was independent of the excitation wavelength although Table 2. Samples AF/9/E, AF/88/IL6 and HF_B are also presented in Finch et al (2016), where HF_B is labelled as AF/07/35 the intensity under LW was generally stronger than under SW excitation. The luminescence spectroscopy of AF/9/E, AF/88/IL6 and HF_B are presented in Finch et al (2016); the latter sample is labelled AF/07/35 in Finch et al (2016).…”

“…Samples AF/9/E, AF/88/IL6 and HF_B are also presented in Finch et al (2016), where HF_B is labelled as AF/07/35 the intensity under LW was generally stronger than under SW excitation. The luminescence spectroscopy of AF/9/E, AF/88/IL6 and HF_B are presented in Finch et al (2016); the latter sample is labelled AF/07/35 in Finch et al (2016). All tenebrescent samples showed the same induced purple colour, but with varying intensity and were grouped into strongly tenebrescent ("Strong"), tenebrescent ("Yes") and not tenebrescent ("No") in some of the figures below.…”

“…Thus, the observed decrease in the Fe concentration cannot be the promoter of tenebrescence which must be the result of other so far unknown mechanisms. We have not performed Mössbauer spectroscopy on our samples, and therefore, we solely base our assumption that Fe is trivalent on the fact that the luminescence of HF_B has a typical Fe 3+ emission (Finch et al 2016). Ballentyne and Bye (1970) showed that Se and Te can cause tenebrescence.…”

A high sensitivity system for luminescence measurement of materials

“…Wang et al). We readily observe TL in less sensitive dosimeter materials, including alumina, quartz, feldspar and sodalite . We improve signal‐to‐noise in the least sensitive materials by increasing the initial dose (longer X‐irradiation times) and/or the temperature ramp rate.…”

“…The system is normally operated with 500 μm slits but these can be opened to 1000 μm, broadly increasing the signal four‐times. Dimmer materials such as poorly responsive diamond, quartz and feldspar have been successfully measured on the system, but here we present novel data for the framework silicate sodalite . XEOL data can be obtained as a function of temperature and incident power (e.g.Wang et al).…”