Epifluorescence optical microscopy: a sensitive tool for determining the spatial distribution of europium-dihalide precipitates in KCl: KBr: Eu~(2+) crystals

摘要

The spatial distribution of europium-dihalide-type precipitates in KCl: KBr :Eu~(2+) single crystals annealed at 200 deg C for long periods of time was determined by epifluorescence optical microscopy. Laue-type patterns and optical spectroscopy were used to test the degree of long-range ordering of the specimens and to monitor the precipitation during annealing, respectively. Precipitates smaller than about 0.08 mu m were found (2.84 x 10~(12) precipitates cm~(-3)) all across the host, whereas larger precipitates of about 0.17 mu m were found (2.9 X 10~4 precipitates cm~(-1)) along certain linear structural singularities of the matrix. These singularities, identified as crystal dislocations, were observed to terminate always either at a triple node of singularities or at the crystal surface, forming a three-dimensional network of crystal singularities (2.0 X 10~6 singularities cm~(-2)), identified as the Frank network. The presence of europium exhaustive matrix zones accompanying the observed europium-decorated paths indicates that impurity segregation processes, occurring during annealing, favour the precipitation phenomena.