Kumar R, Martin L I D J, Poelman D, Vandenberghe D, De Grave J, Kook M, Jain M
Department of Physics, Technical University of Denmark, DTU Risø Campus, 4000, Roskilde, Denmark.
Department of Solid-State Sciences, Ghent University, 9000, Ghent, Belgium.
Sci Rep. 2020 Sep 24;10(1):15650. doi: 10.1038/s41598-020-72334-7.
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's 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 ~ 6 to 22 µm. 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 model that explains the quenching of the NIR emission by Fe. Our study contributes to an improved understanding of charge storage in feldspathic minerals, with implications for developing sub-single grain (micrometer scale) measurement techniques in radiation dosimetry.
由晶体缺陷中的电子或空穴俘获所产生的亚稳态在剂量测定和光子学应用中被广泛使用。长石是地壳中最丰富的矿物（>50%），在受到电离辐射时会产生寿命达数百万年的亚稳态。尽管长石在剂量测定和地质年代学中被广泛应用，但对亚稳态的产生以及电荷在其中的转移了解甚少。理解此类现象需要基于对亚稳态进行高分辨率、位点选择性探测的新一代方法。最近利用诸如7K下的光致发光（PL）和辐射发光（RL）等位点选择性技术的研究表明，长石呈现出两个近红外（NIR）发射带，峰值分别在880nm和955nm，据信这两个发射带源于主要的电子俘获态。在此，我们首次使用光谱分辨阴极发光显微镜以约6至22μm的空间分辨率绘制了富钾长石中的电子俘获态。由扫描电子显微镜探测的每个像素为我们提供了600 - 1000nm范围内的阴极发光光谱（SEM - CL）以及能量色散X射线（EDX）光谱的元素数据。我们得出结论，这两个近红外发射在空间上是可变的，因此源自不同的位点。这一结论与现有的模型相矛盾，现有模型认为这两个发射源于一个主要陷阱的两个不同激发态。此外，我们能够将各个近红外发射峰与地球化学变化（钾、钠和铁浓度）联系起来，并提出一个解释铁对近红外发射猝灭的模型。我们的研究有助于增进对长石矿物中电荷存储的理解，对开发辐射剂量测定中的亚单颗粒（微米尺度）测量技术具有重要意义。
