X-Ray induced luminescence as a tool for material characterisation in art and archaeology

Analytical techniques based on luminescence properties of materials have already revealed to be interesting for different purposes in art and archaeology. For example, cathodoluminescence (CL) coupled with optical microscopes or scanning electron microscopes and iono-luminescence (IL) installed on proton probe beamlines proved to be very useful for identification of mineralogical phases and for provenance studies. Although the above-mentioned approaches actually give valuable information, the potentiality of luminescence-based techniques has not yet been fully exploited, due to the lack of portability, a great limitation in the field of Cultural Heritage. To overcome these limitations and to investigate the potential of a scarcely used technique in this field, a test apparatus for X-Ray induced Luminescence (XRL) was developed in the framework of the INFN-CHNet collaboration. X-rays as excitation source were chosen because they are non-invasive and potentially integrable in a portable XRF/XRD apparatus. The prototype is based on a X-ray tube and a cooled-spectrometer collecting the induced light through an optical fibre. The first results are encouraging. In fact, the XRL was applied to the characterisation of lapis lazuli stones and it allowed us to discriminate among some different provenances in a similar way to what obtained i.e. with CL and IL [2,4]. For example in Fig. 1 the double broad band typical of wollastonite, a mineral widely spread only in the Chilean rocks, allows discriminating the stones of this origin from those of Afghan provenance that, as other Asian lapis lazuli, are rich in diopside, a mineral showing its peculiar band centred at 585 nm.