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Lanthanide-based upconverting and chromium-based persistent luminescence nanoparticles for optical applications involving NIR illumination

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Author(s):
York Estewin Serge Correales
Total Authors: 1
Document type: Doctoral Thesis
Press: Araraquara. 2023-01-18.
Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
Defense date:
Advisor: Sidney José Lima Ribeiro
Abstract

This work reports the development of luminescent materials with upconversion (UC) and persistent luminescence (PL) properties for optical applications involving near-infrared (NIR) illumination. The following are described and discussed: 1) controlled synthesis to obtain uniform and monodisperse nano- and micro-particles; 2) surface modification to provide hydrophilic functional groups, making them dispersible and stable in aqueous media; 3) the structural, morphological, optical and photoluminescent characterizations; 4) potential applications. Sub-20 nm core/multishell NaGdF4:Yb3+/Ca2+/Nd3+/Tm3+@NaGdF4:Nd3+/Ca2+@ NaGdF4:Yb3+/Ca2+/Er3+/Nd3+ UC nanoparticles (UCNPs) were obtained by seed-mediated growth via high-temperature co-precipitation route. Through simple and precise control of the shell thickness along with tuning the content of lanthanide ions in each domain (core, middle shell, and outermost shell) it was possible to obtain multicolored and tunable luminescence from blue to white under 808 nm laser excitation. NaYbF4:Tm3+ UC particles (UCPs) with microrod shape of 8 µm in length and 2.5 µm in diameter were also synthesized. These microrods in conjunction with Ag3PO4 particles (photocatalyst) and H2O2 (oxidizing agent) were used in the development of a broad-spectrum photocatalytic system, active in the UV-Vis-NIR region. This photocatalytic system showed high photocatalytic activity in crystal violet (CV) dye degradation under both direct excitation with visible light (complete dye removal in less than 8 min) and indirect excitation of Ag3PO4 in the NIR due to photons emitted by the UCPs under 980 nm laser irradiation (almost total dye removal in approximately 90 min). Furthermore, uniform OA-capped NaYbF4:Tm3+@NaYF4 core/shell UCNPs were synthesized. The UC property of these nanoparticles was improved by increasing the protection of the NaYbF4:Tm3+ core nanoparticles with a NaYF4 protective layer of different thickness. Increasing shell thickness led to a concomitant decrease in energy quenching associated with surface defects of the unprotected nanoparticles. To enhance the applications of these NaYbF4:Tm3+@NaYF4 UCNPs, their coupling with PL nanoparticles (PLNPs) was investigated, aiming at obtaining a system that presents UC and PL (UC-PL) with excitation and emission in the NIR, which may find potential applications in deep tissue luminescence bioimaging or in the activation of photosensitizers in the photodynamic therapy. As a result, OA-coated ZnGa2O4:Cr3+ (ZGO) PLNPs were first synthesized. The synthesis was carried out by solvothermal treatment at 210 °C, without the need for further calcination. Tunable size from 7 to 21 nm was achieved using different alcohols in the synthesis and a seed-mediated nanoparticle growth approach. The PL was nanoparticle size-dependent (PL lasting over 1000 s). After improving the optical properties of the OA-coated nanoparticles, the ligand exchange process for surface modification was carried out. This allowed removing hydrophobic ligands and anchoring hydrophilic groups provided by poly(acrylic acid) (PAA) polymer and cysteamine (Cys) molecules on the surface of the nanoparticles, ensuring their redispersion in aqueous media, as well as providing long-term colloidal stability. Finally, the coupling reactions of hydrophilic nanoparticles were investigated through the formation of covalent bonds between surface-functionalized UCNPs and PLNPs, on the basis of EDC/NHS (1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide hydrochloride)/(N-Hydroxysuccinimide) coupling chemistry. The results obtained suggest that the coupling reaction was successfully performed. However, new coupling conditions and characterizations are needed, as well as the study of the energy transfer between the nanoparticles for a better understanding of this coupling process and to guarantee future applications. (AU)

FAPESP's process: 18/15791-7 - Lanthanide-doped luminescent nanomaterials: synthesis and applications
Grantee:York Estewin Serge Correales
Support Opportunities: Scholarships in Brazil - Doctorate (Direct)