Epifluorescence microscopy: a sensitive tool for studying the morphology and oriented growth of europium precipitates...

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.