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Metastable states created by electron or hole capture in crystal defects arewidely used in dosimetry and photonic applications. Feldspar, the most abundantmineral in the Earth crust (>50%), generates metastable states with lifetimesof millions of years upon exposure to ionizing radiation. Although feldspar iswidely used in dosimetry and geochronometry, the creation of metastable statesand charge transfer across them is poorly understood. Understanding suchphenomena requires next-generation methods based on high-resolution,site-selective probing of the metastable states. Recent studies usingsite-selective techniques such as photoluminescence (PL), and radioluminescence(RL) at 7 K have revealed that feldspar exhibits two near-infrared (NIR)emission bands peaking at 880 nm and 955 nm, which are believed to arise fromthe principal electron-trapping states.  Here, we map for the first time the electron-trapping states inpotassium-rich feldspar using spectrally-resolved cathodoluminescencemicroscopy at a spatial resolution of around 6 to 22 micrometer. Each pixelprobed by a scanning electron microscope provides us a cathodoluminescencespectrum (SEM-CL) in the range 600-1000 nm, and elemental data fromenergy-dispersive x-ray (EDX) spectroscopy. We conclude that the two NIRemissions are spatially variable and, therefore, originate from differentsites. This conclusion contradicts the existing model that the two emissionsarise from two different excited states of a principal trap. Moreover, we areable to link the individual NIR emission peaks with the geochemical variations(K, Na and Fe concentration), and propose a cluster model that explains thequenching of the NIR emission by Fe4+.

Site-selective mapping of metastable states using electron-beam induced luminescence microscopy