  Metastable states created by electron or hole capture in crystal defects are
widely used in dosimetry and photonic applications. Feldspar, the most abundant
mineral in the Earth crust (>50%), generates metastable states with lifetimes
of millions of years upon exposure to ionizing radiation. Although feldspar is
widely used in dosimetry and geochronometry, the creation of metastable states
and charge transfer across them is poorly understood. Understanding such
phenomena requires next-generation methods based on high-resolution,
site-selective probing of the metastable states. Recent studies using
site-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 from
the principal electron-trapping states.
  Here, we map for the first time the electron-trapping states in
potassium-rich feldspar using spectrally-resolved cathodoluminescence
microscopy at a spatial resolution of around 6 to 22 micrometer. Each pixel
probed by a scanning electron microscope provides us a cathodoluminescence
spectrum (SEM-CL) in the range 600-1000 nm, and elemental data from
energy-dispersive x-ray (EDX) spectroscopy. We conclude that the two NIR
emissions are spatially variable and, therefore, originate from different
sites. This conclusion contradicts the existing model that the two emissions
arise from two different excited states of a principal trap. Moreover, we are
able to link the individual NIR emission peaks with the geochemical variations
(K, Na and Fe concentration), and propose a cluster model that explains the
quenching of the NIR emission by Fe4+.
