Abstract
Europium(III) (Eu3+/Eu(III)) substitution in the hydroxyapatite (HAp) lattice imparts luminescence properties, enabling its application in diagnostics and bioimaging. Despite numerous experimental studies, there has been a lack of comprehensive discussion on the substitution behavior and local structural stability of Eu3+ within HAp. In this study, experimental and first-principles investigations were integrated to explore and understand the substitution of Eu3+ in HAp. Optimization of various HAp models revealed the dependency of Eu3+ substitution site on the charge compensation mechanism. Eu3+ prefers the Ca(2) site when OH is converted to O and the Ca(1) site in the presence of a Ca vacancy. Phonon calculations showed that temperature influences charge compensation and site preference, favoring OH to O compensation and Eu3+ in Ca(2) at higher temperatures and Ca vacancy and Eu3+ in Ca(1) at lower temperatures. Electronic structure simulations explained that the luminescence in Eu(III)-substituted HAp primarily arises from charge transfer between Eu3+ and O atoms, supported by experimental photoluminescence measurements. Correspondence between simulations and experimental photoluminescence data emphasizes the reliability of the computational approach in this study. The integration of insights from experimental and simulation results enhances the understanding of substitution of Eu3+ in the HAp lattice, providing valuable guidance for designing and optimizing HAp-based luminescent and optical materials.
Published Version
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