Epifluorescence microscopy: A sensitive tool for studying the morphology and oriented growth of europium precipitates in KI single-crystal hosts
Por:
CorderoBorboa, AE, UndaAngeles, R
Publicada:
1 jun 2015
Resumen:
The morphology and oriented growth of europium precipitates in well-annealed Eu2+-doped KI single crystals are investigated by epifluorescence microscopy using the proper doping ions as fluorochromes. To make this, electronic spatial reconstructions of some fields of precipitates and of some individual precipitates were built from epifluorescence microscope images of different optical cross-sections of these objects. The building procedures are carefully explained. Previously, the KI:Eu2+ system was characterized by fluorescence spectrophotometry and the KI-host long-range translational order was tested by single-plate X-ray diffraction. Precipitates are shaped as plates, with their broad faces being parallel to host lattice planes of either {100}- or {110}-forms (the {100}- or {110}-plates, respectively) and as rods lying along host lattice <100>-directions. The {100}-plates have rhomboidal broad faces with a side lying along a <100>-direction, an internal angle of about 45°, as measured on the corresponding {100}-plane, and, consequently, another side (the {100}<110>-side) lying along a <110> direction on this plane. The {110}-plates have rectangular broad faces with a side lying along a <100>-direction and with another side (the {110}<110>-side) lying along a <110>-direction on the corresponding {110}-plane. Spatial reconstructions of a typical precipitate field, a typical {100}-plate, a typical {110}-plate and a typical rod are described in detail. Precipitates were measured in their different dimensions and the measuring procedures are explained. The plate thicknesses and rod diameters are into a common narrow range of values (0.5-0.2 µm) which contains also the inferior limits of the obtained length ranges for the {100}<110>- and {110}<110>-sides (5.1-0.3 and 4.9-0.3 µm, respectively). It is discussed that that three different europium precipitation states are responsible for the studied precipitation and that plates grew from rods during annealing. Lay description: Alkali-halide crystals doped with europium ions have an optical behaviour that may be used, among other applications, to know the amounts of ultraviolet radiation that might reach our bodies during particular situations, like sun exposure, causing skin burns and erythema, or of gamma-ray radiation delivered at the patient during cancer radiotherapy. In this paper, shapes and orientations adopted by europium precipitates in europium-doped KI crystals are investigated by a particular type of microscopy (epifluorescence microscopy) based on the fact that doping europium emits blue light immediately after being illuminated with ultraviolet light. To investigate this, electronic spatial reconstructions of some fields of precipitates and of some individual precipitates were built from microscope images of these fields and precipitates. The building procedures are carefully explained. Precipitates are shaped as plates and rods. In relation with a cube commonly used to study the KI structure, plate-shaped precipitates are on cube faces (the {100}-plates) or on planes defined by opposite cube edges (the {110}-plates) whereas rod-shaped precipitates are along cube edges. The {100}- and {110}-plates have their broad faces shaped as rhomboids and rectangles, respectively. A side of both rhomboidal and rectangular faces is aligned with cube edges (the {100}<100>- and {110}<100>-sides, respectively). Rhomboidal faces have another side (the {100}<110>-side) making an angle of about 45° with their {100}<100>-side, as measured on a cube face containing this last side. Rectangular faces have another side (the {110}<110>-side) making an angle of about 90° with their {110}<100>-side as measured on t cube face that is perpendicular to this last side. Spatial reconstructions of a typical field of precipitates, as well as three typical precipitates are described in detail. Precipitates were measured in their different dimensions and the measuring procedures are explained. From such measurements and the observed existence of precipitates with three different morphologies, it is discussed that three different europium aggregation-precipitation states are responsible for the precipitation and, also, that plates grew from rods during annealing. © 2015 Royal Microscopical Society.
Filiaciones:
CorderoBorboa, AE:
Univ Nacl Autonoma Mexico, Inst Fis, Mexico City 01000, DF, Mexico
UndaAngeles, R:
Univ Nacl Autonoma Mexico, Inst Fis, Mexico City 01000, DF, Mexico
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