Browsing by Author "Unal, Ugur"

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Citation - WoS: 6
Citation - Scopus: 6
Synthesis of Upconverting Nanosheets Derived From Er-Yb and Tm-Yb Co-Doped Layered Perovskites and Their Layer-By Assembled Films
(Elsevier, 2022) Gunay, Bensu; Suer, Ozge; Doger, Hilal; Arslan, Ozlem; Unal, Ugur; Saglam, Ozge
Here, we investigated the structure and upconversion (UC) properties of new-type of single oxide nanosheets, derived from the Er3+/Yb3+ and Tm3+/Yb3+ co-doped Ruddlesden-Popper type layered perovskites, and their layer-by-layer (LBL) self-assembled nanofilms. The single oxide nanosheets, obtained by exfoliation of the proton-exchanged K2La2Ti3O10, had the thickness in the range of 2-3 nm indicating good consistency with the theoretical thickness and lateral size from 500 nm up to 2 mu m. Er3+/Yb3+, Tm3+/Yb3+ and Tm3+/Er3+co-doped nanosheets were used as building blocks of the multilayer films deposited by layer-by-layer procedure. The LBL films composed of 2.5 % Er3+ + 5 % Yb3+, 2.5 % Tm3+ + 20 % Yb3+, 2.5 % Tm3+ + 20 % Er3+ after 60 sequences have shown a white emission confirmed by the CIE chromaticity diagram. The possible UC energy transfer of LBL films fabricated after 30 sequences using the nanosheets derived from the 2.5 % Er3+ + 5 % Yb3+ co-doped layered perovskites was also suggested. The number of photons participating in the UC process was confirmed as two-photon for both green and red UC emissions due to the F-4(9/2) -> I-4(15/2) and H-2(11/2), S-4(3/2) -> I-4(15/2) transitions, respectively.
Citation - WoS: 10
Citation - Scopus: 11
Upconversion Properties of Tm3+-Er3+ Co-Doped Layered Perovskites and In-Vitro Cytotoxicity of Their Exfoliated Nanomaterials
(Elsevier, 2021) Gunay, Bensu; Sariyar, Ece; Unal, Ugur; Karagonlar, Zeynep Firtina; Saglam, Ozge
The upconversion behavior of Er3+/Tm3+ co-doped Ruddlesden-Popper type K(2)Ln(2)Ti(3)O(10) layered perovskites was investigated. The lanthanide pair was selected for achieving 980 nm-driven green, red, and NIR emission. The perovskites having different dopant compositions were synthesized by a conventional solid-state procedure by substitution of La3+ ions in the host lattice. Moreover, the single nanosheets having approximately 1.8 nm thickness and 2 mu m lateral size were obtained via chemical exfoliation. The non-doped and co-doped layered materials and the nanosheets derived from these materials were characterized by X-ray diffraction, Scanning Electron Microscopy, Atomic Force Microscopy and custom-made experimental set-up of upconversion emission spectroscopy. According to the XRD profiles, the perovskites had the layered orientation and water molecules in the interlayer domain because of their hygroscopic nature. The co-doped layered perovskites presented twophoton excited green and red emissions, identified as S-4(3/2) -> (4)I(15/2 )with H-2(11/2) -> (4)I(15/2 )and F-4(9/2) -> I-4(15/2) of the Er3+ transitions with a NIR emission. The intensity of red to green ratio emission of the materials increased with respect to the co-dopant concentration. The nanosheets' upconversion emission was weak in the visible region compared to their layered morphology. On the other hand, the NIR emission based on H-3(4) -> H-3(6) transition of the Tm3+ ions was preserved despite the acid and solvent treatments to break apart the layered orientation. MTT assay and Calcein/PI staining were conducted to evaluate cytotoxicity of non-doped and Er3+/Tm3+ co-doped K(2)Ln(2)Ti(3)O(10) perovskites and their exfoliated nanosheets on HEK 293 and HepG2 cell lines. Both assays indicated that although cell viability decreases with increasing concentration, good cell viability was observed at even 100 mu g/mL. In addition to their excellent luminescent and optical features, the nanomaterials also demonstrated low cytotoxicity increasing the potential for their use in laser-based biological applications.