Investigating the origins of long persistence in strontium aluminate phosphors by nanoscale resolved imaging and spectroscopy
İnan Akmehmet, Güliz (2015) Investigating the origins of long persistence in strontium aluminate phosphors by nanoscale resolved imaging and spectroscopy. [Thesis]
With a remarkable capacity to temporarily store and release light, long persistence phosphors are an exciting material for energy-saving applications. The objective of this work is to elucidate the role of B in dramatically extending persistence in strontium aluminate doped with Eu, Dy from the order of minutes to > 8 hours. Previous work neglected nanoscale effects. Computational models and experimental evidence, limited to indirect, global analysis, suggested that the extended afterglow may be due to the clustering of ionic point defects, although the results are inconclusive. However, in recognizing that high spatial resolution techniques of transmission electron microscopy (TEM) offer a game-changing advantage for localized analysis, this dissertation is devoted to the application of techniques with spatial resolution at the nanoscale and atomic scale for correlating the material structure with optical properties.To set the stage, the processing of ceramic phosphor powders by a modified Pechini process was methodically studied. After global characterization of the powder structure optical properties, we have defined the atomic resolution TEM experimental techniques and simulation tools that will be necessary for quantitatively elucidating the defect clustering model. Our key results demonstrate that B, entering the compound in trigonal coordination, facilitates dominance of the long persistence Sr4Al14O25 phase in the developing microstructure and promotes a more uniform distribution of divalent Eu onto the Sr sublattice. With such unprecedented correlation between structure and optical properties at the nanoscale, our results invite revision to existing models of persistence in strontium aluminate phosphors.
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