Spectral variability of the uranyl silicates uranophane-α and uranophane-β: polymorphism and luminescence

IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY
Martin Stark, Markus Noller
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Abstract

The luminescence of the uranyl cation UO22+ depends on the local crystalline environment and is sensitive to structural influences. Steady-state photoluminescence emission spectra of the related uranyl silicates uranophane-α, uranophane-β, sklodowskite and haiweeite from various locations are presented and discussed in the light of structure–property relation. The four mineral species were chosen for their close relationships: uranophane-α and uranophane-β are polymorphs and share the underlaying topology with sklodowskite. Haiweeite, with different topology, shares the composing elements Ca, U, Si, O with uranophane, while in sklodowskite Mg replaces Ca. All species show some variability in their spectra, parameterized as a variation of the centroid wavelength. Those variations are linked to defects and structural disorder, relevant in studies of uranyl speciation and migration. We present empiric spectra of the four mineral species with the least influence of structural disorder. As an unexpected feature, a prominent—partly dominating—double peak structure occurs in the case of uranophane-α only, while it is absent in the spectra of the other species. Considering a model of luminescent transitions in the uranyl ion in more detail, this observation is discussed in the light of the polymorphism of uranophane. We show evidence that variable amounts of uranophane-β phase embedded in uranophane-α are possibly at the origin of this spectral signature. Growth of those uranophane-β clusters might be induced by defects in the uranophane-α lattice and further promoted by the polymorphism of uranophane.

Abstract Image

铀酰硅酸铀-α和铀-β的光谱变异性:多态性和发光
铀酰阳离子UO22+的发光取决于局部晶体环境,对结构的影响很敏感。本文给出了不同产地的相关铀酰硅酸盐(铀酰-α、铀酰-β、sklodowskite和haiweeite)的稳态光致发光光谱,并从构效关系的角度进行了讨论。选择这四种矿物是由于它们之间的密切关系:天王星-α和天王星-β是多晶型矿物,与sklodowski矿具有相同的下伏拓扑结构。不同拓扑结构的海威石与铀芬石共有Ca、U、Si、O组成元素,而sklodowskite中的Mg取代了Ca。所有物种的光谱都表现出一定的变异性,参数化为质心波长的变化。这些变异与缺陷和结构紊乱有关,与铀酰形成和迁移的研究有关。我们给出了结构紊乱影响最小的四种矿物的经验光谱。作为一个意想不到的特征,一个突出的-部分主导-双峰结构出现在天王星-α的情况下,而它在其他物种的光谱中不存在。考虑到铀酰离子中发光跃迁的一个更详细的模型,这一观察结果在铀酰的多态性的光进行了讨论。我们发现证据表明,在天王星-α中嵌入的不同数量的天王星-β相可能是这个光谱特征的起源。这些天王星-β簇的生长可能是由天王星-α晶格缺陷诱导的,并进一步受到天王星多态性的促进。
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来源期刊
Physics and Chemistry of Minerals
Physics and Chemistry of Minerals 地学-材料科学:综合
CiteScore
2.90
自引率
14.30%
发文量
43
审稿时长
3 months
期刊介绍: Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)
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