Abstracts

With the ever-increasing development and optimization of optical properties in rare-earth-doped persistent phosphors, several bottom-up engineering methods have been widely studied for the fabrication of multifunctional luminescent materials with a wide range of applications. In this work, tris-Eu³⁺ β-diketonate hydrate complexes (e.g. tta: thenoyltrifluoroacetonate, or dbm: dibenzoylmethanate) were prepared by coprecipitation and later coordinated with ancillary ligand 4-picoline-N-oxide. The prepared complexes were then functionalized on SrAl₂O₄:Eu²⁺,Dy³⁺ persistent phosphors by microwave-assisted silanization using (3-Aminopropyl)trimethoxysilane as a precursor for both single and double-shell structures. Powder X-ray diffraction (PXRD) analysis revealed the presence of the characteristic SrAl₂O₄ stuffed tridymite structure alongside SrCO₃ by-product due to annealing under a reducing carbon monoxide atmosphere. Additionally, surface silanization resulted in an amorphous SiO₂ network, as seen by PXRD and electron microscopy and energy-dispersive X-ray spectroscopy results, the latter also probing dopant distribution as well as the effectiveness of the silanization method. Luminescence spectroscopy revealed that single-shell materials exhibit a different emission profile for both tta and dbm complexes, with predominant Eu²⁺ and Eu³⁺ emission, respectively. On the other hand, double-shell phosphors show intense red luminescence derived mainly from the complexes during excitation. Long-lasting persistent luminescence was also observed in functionalized materials, where the single-shell phosphor functionalized with the europium tta complex displayed the highest persistence decay time. Furthermore, vacuum-ultraviolet emission spectra recorded under direct SrAl₂O₄ band-gap excitation corroborate with UV-Vis data, with predominant Eu²⁺ green emission. Finally, site-selective luminescence in functionalized materials was carried out at the Brazilian synchrotron (Sirius) combining X-ray fluorescence, X-ray absorption near edge structure, and X-ray excited optical luminescence spectroscopy experiments. Results showed that the ratio between Eu²⁺ and Eu³⁺ emission is intrinsically different for the edge and the bulk of the studied particles with possible energy-transfer (ET) in the interface of the SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor, and the europium complexes embedded into the silica shells on distinct regions for a single particle. Such results revealed the influence of shell thickness and distance in ET processes, outlining an important framework for the development of multifunctional persistent phosphors utilizing rare-earth complexes as luminescent sensitizers.References:[1] Y. Li, M. Gecevicius, J. Qiu, et al. Chem. Soc. Rev. 45 (2016) 2090-2136.[2] L.H.C. Francisco, R.P. Moreira, M.C.F.C. Felinto, et al. J. Alloys Compd. 882 (2021) 160608.