Luminescence spectroscopy and microscopy
Luminescence is an important and insightful property that provides information about the electronic properties of a material. In Earth and Environmental sciences, luminescence is particularly used for radiation dosimetry and dating. At St Andrews , we have been particularly interested in luminescence to understand the structural states of rock-forming minerals to reconstruct past cooling and uplift rates.
EEA includes laboratories dedicated to both luminescence dating and luminescence spectroscopy. For spectroscopy, we excite the sample with UV-visible radiation (photoluminescence, PL), an electron beam (cathodoluminescence, CL) or by implantation with ion beams (ionoluminescence IL, developed with School of Engineering , University of Sussex). The development of IL was the subject of a standard NERC grant award in 2000.
Photoluminescence (PL)
The school has a SPEX industries Fluorolog 2 spectrometer with a Xe lamp primary source with a double spectrometer and cooled PMT to record the secondary luminescence. The system was comprehensively upgraded in 2004. The Xe excitation can be tuned by a single monochromator through the UV-visible range (typically 200-400 nm) and luminescence can be measured between 300 and 850 nm. The Xe lamp source can be replaced by lasers. Real time stimulation experiments (i.e. using low energy primary radiation) can also be performed with residence times as low as 10 us. Samples are usually crystal cleavage fragments, compressed polycrystalline discs or polished thin sections (without cover-slips). The PL manual can be found here.
Cathodoluminescence (CL)
FEEA houses a Technocyn Mark 4 CL (with a 15 kV flood-gun type electron source) attached to a Nikon Optiphot microscope and a DVC high-sensitivity colour digital camera .
Samples are usually polished thin sections without cover-slips. At 12 kV with a current of 600 uA, for example, exposure times for minerals are typically 4-8 s.
The CL microscope is used to example polyphase ceramics or rocks as an aid to mineral identification. It is also used to determine heterogeneity within individual minerals, prior to microanalysis by SIMS, LA-ICPMS or EPMA. Cathodoluminescence manual (PDF, 133 KB).
The EPMA facility also has a monochromatic CL system attached to the electron probe microanalysis instrument which records fast (us) decaying luminescence at micron scales. The detector is a JXA-733 photomultiplier tube with a response in the range 400-650 nm. Although this system is monochromatic, it has submicron image resolution and can be combined with backscattered electron imaging of the same areas. Such methods are particularly important precursors to e.g., SHRIMP dating of zircons.
Ionoluminescence (IL)
The School is involved in a collaborative work with the School of Engineering at the University of Sussex to develop IL in minerals. IL is carried out under vacuum using the 3 MeV van de Graaff particle accelerator facility at the University of Sussex. Samples are mineral cleavage fragments or polished thin sections. The ion beam can be focussed to a spot of ~0.25 cm2 and the responses examined as a function of temperature, implantation dose and the nature of the accelerated ion. Typical primary ions are H+ , H2+ , He+ and N+ . Data are collected between 40 K and room temperature using an 8 W He closed cycle cryogenic compressor. Light emissions are collected by a quartz fibre optic coupled to a f/4 SpectroPro 300i monochromator . The detector used was a Roper Scientific image intensified CCD camera operated using the WinSpec software package. The system normally operates in the range 200-1100 nm using a coarse grating to perform two separate spectral analyses between 200-600 and 500-1100 nm respectively and then matching the spectra in the 500-600 nm region.
Ionoluminescence manual (PDF, 328 KB)
