Structural characteristics in long afterglow strontium aluminate compounds: An investigation with Raman and FTIR spectroscopy

Official URL: https://risc01.sabanciuniv.edu/record=b2758676_(Table of contents)

Europium (Eu2+), dysprosium (Dy3+), and boron (B) co-doped strontium aluminate compounds emitting persistent luminescence (PersiL) are well-known for offering illumination with zero energy consumption making them attractive for use in safety signage and paint. Although B is well known to extend the persistence of luminescence from Eu and Dy co-doped strontium aluminates, it is not clear how B induces the formation of the material structure that supports extreme afterglow. Previous work suggests that B incorporates interstitially into Sr4Al14O25: Eu, Dy. The objective of this dissertation is to elucidate how B directs the atomic arrangements in such compounds. To set the stage, we applied materials characterization tools that reveal information about short-range order and localized environments, FTIR and Raman spectroscopy. Because micro-Raman reveals spatially resolved information at the micrometer scale, it is particularly well suited for analyzing strontium aluminate pigments, which can be produced with micron-sized grains. Eu and Dy co-doped Sr4Al14O25 (S4A7ED) synthesized with 30-40 mol% B2O3 displayed the longest duration of PersiL, and these compositions do not contain the highest amount of the long persistence phases. Instead, an optimal amount of B is necessary for the incorporation of electrically charged, non-bridging oxygen (NBO) into the doped S4A7ED crystal structure. The use of oxide glass forming precursors of Si, P, and Zr during Pechini processing also extended PersiL in S4A7ED compounds and was correlated with structural changes arising from NBO incorporation. Through the experimental evidence revealed in this work, we discovered a new class of long afterglow compounds.