Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 2Citation - Scopus: 31-Octanol Is a Functional Impurity Modifying Particle Size and Photophysical Properties of Colloidal Zncdsse/Zns Nanocrystals(American Chemical Society, 2021) Sevim Ünlütürk, Seçil; Özçelik, Serdar; Çağır, Ali; Varlıklı, Canan; Varlıklı, Canan; Çağır, Ali; Özçelik, Serdar; 04.01. Department of Chemistry; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyImpurities in trioctylphophine (TOP) strongly affect nanocrystal synthesis. 1-Octanol among other contaminants in TOP is identified for the first time as a functional impurity by H-1 NMR. The deliberate addition of 1-octanol into trioctylphosphine reduced particle size and modified photophysical properties of ZnCdSSe/ZnS colloidal nanocrystals. NMR analysis furthermore revealed that 1-octanol is bonded to the nanocrystal surfaces. The ratio of integrals for the O-CH2 protons of 1-octanol, which is the lowest compared to the other ligands, suggests that 1-octanol plays a critical role to tune the particle size of nanocrystals. The increased amount of 1-octanol added into TOP reduces the particle size from 9.8 to 7.2 nm, causing a progressive blue shift in the UV-vis and PL spectra but leaving the alloy composition unaffected. The rate of nonradiative processes is enhanced with the amount of 1-octanol added into TOP, correlating with higher dislocation density observed in the nanocrystals. As a conclusion, 1-octanol is proposed as a functional impurity that varies particle size and nonradiative photophysical processes in the ZnCdSSe/ZnS colloidal nanocrystals.Article Citation - WoS: 8Citation - Scopus: 8Reducing the Efficiency Roll Off and Applied Potential-Induced Color Shifts in Cdse@zns/Zns-based Light-Emitting Diodes(American Chemical Society, 2020) Özgüler, Şahika; Varlıklı, Canan; Diker, Halide; Özçelik, Serdar; Ünlütürk, Seçil Sevim; Diker, Halide; Özçelik, Serdar; Varlıklı, Canan; 01. Izmir Institute of Technology; 04.01. Department of Chemistry; 04.04. Department of Photonics; 04. Faculty of ScienceGreen light-emitting CdSe@ZnS/ZnS (QD) nano-particles were synthesized; the photophysical and morphological properties of their films, which were prepared by spin coating from six different concentrations, corresponding to absorbance values of 0.6, 1.1, 1.6, 2.1, 2.8, and 4.0, were determined. Increasing the absorbance value from 0.6 to 4.0 did not change the photophysical properties of QD films to a large extent, whereas it resulted in an increment in QD film thickness from 20 to 110 nm. The films were utilized as an emissive layer in QD light-emitting diodes with poly(9-vinylcarbazole) (PVK), PVK:2-(4-biphenyllyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), and PVK:1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]-phenylene (OXD-7) hole-transport layers (HTLs). The presence of PBD or OXD-7 in PVK reduced the efficiency values but played a positive role in the color purity and efficiency roll off. The maximum color temperature and electroluminescence wavelength shifts obtained with applied potential were 109, 50, and 50 K and 11, 5, and 5 nm for pure-PVK, PVK:PBD, and PVK:OXD-7-based devices, respectively. Hole mobility, capacitance (at 10(3) Hz), and charge-transfer efficiency values were 9.0 x 10(-7), 6.8 x 10(-7), and 4.2 x 10(-7) cm(2) V s(-1), 1.7, 1, and 1 nF, and 6.90%, 15.50%, and 16.10% for pure-PVK, PVK:PBD, and PVK:OXD-7-based devices, respectively. Enhanced color purity and lowered efficiency roll off obtained with PVK:PBD and PVK:OXD-7 HTLs were attributed to decreased capacitance, increased charge-transfer efficiency, and reduced Joule heating.Article Citation - WoS: 7Citation - Scopus: 7An Ultraviolet Photodetector With an Active Layer Composed of Solution Processed Polyfluorene:zn0.71cd0.29s Hybrid Nanomaterials(Elsevier Ltd., 2014) Sevim, Seçil; Memişoğlu, Görkem; Özçelik, Serdar; Doğan, Leyla Eral; Taşçıoğlu, Didem; Varlıklı, Canan; 04.01. Department of Chemistry; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyAn ultraviolet photodetector with an active layer of solution processed polymer:quantum dot hybrid is introduced. Poly[9,9-di-(2-ethylhexyl)-fluorenyl- 2,7-diyl] represents the polymer and Zn0.71Cd0.29S is the quantum dot used for the device. Photophysical studies showed that an electron transfer from the polymer to the ternary quantum dot is thermodynamically favored. Quenching experiments performed between the polymer and quantum dot indicates the formation of a non-fluorescent complex with an association constant of 4.6 × 104 M-1. The device structure of ITO/PEDOT:PSS/ADS231BE: 50 wt% Zn0.71Cd0.29S/Al yielded a photoresponsivity value of 324 mA/W at -4 V under 1 mW/cm2 illumination at 365 nm at room temperature and this value is further increased to 380 mA/W as a result of annealing at 75 °C.Article Citation - WoS: 32Citation - Scopus: 32Optical and Electrochemical Properties of Polyether Derivatives of Perylenediimides Adsorbed on Nanocrystalline Metal Oxide Films(Elsevier Ltd., 2013) Kuş, Mahmut; Varlıklı, Canan; Özçelik, Serdar; Varlıklı, Canan; Demiç, Şerafettin; Özçelik, Serdar; İçli, Sıddık; 04.01. Department of Chemistry; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyWe report optical and electrochemical properties of polyether derivatives of perylenediimides (PDIs) thin films formed in various materials (semiconductor, insulator, amorphous and self-assembly). Perylenediimides adsorbed on nanocrystalline TiO2(NT) nanocrystalline alumina (NA), amorphous silicon (PS) and neat self-assemblied (SA) films were prepared and characterized based on spectroscopic, electrochemical, spectro-electrochemical techniques. The absorption and fluorescence spectra of PDIs in chloroform exhibit vibronic features. The fluorescence quantum yields (Uf) of PDIs with end amino substituents in chloroform solutions are over 0.95, while the quantum yield of triethoxyphenyl substituted PDIUfvalue is 0.024 in solution. Optical spectroscopy proves that PDIs in metal oxide thin films form aggregated type complexes. An electrochromism, a color change from red to blue/violet, is observed on metal oxide films, that indicates existence of mono and dianion forms of PDIs. Reversibility of electrochemical reductions in NT film depends on the scanning rate. However, electrochromism in NA films is stable and reversibility is independent from scanning rate. Stable mono and diaionic species are formed on NA films. SA films show broad absorption peaks during the voltammetric scan. On the other hand, the first reduction onset potentials of PDIs are almost equal to the onset potential of capacitive current of TiO2which lead to low efficiency in dye-sensitized solar cells.Article Citation - WoS: 8Citation - Scopus: 8Highly Efficient Orange–red Electroluminescence From a Single Layer Meh-Ppv Hybrid Pled(Elsevier Ltd., 2012) Saygılı, Gamze; Ünal, Gülçin; Varlıklı, Canan; Özçelik, Serdar; 04.01. Department of Chemistry; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyIn this study, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] end capped with polyhedral oligomeric silsesquioxanes (MEH-PPV-POSS): cadmium sulfide selenide quantum dots (CdS0.75Se0.25 QDs) nanocomposites based OLEDs were fabricated. By the addition of CdS0.75Se0.25QDs into the polymer active layer, a considerable enhancement was observed in terms of hole and electron injection in devices. Additionally, the presence of QDs reduced the interchain interaction of polymer that resulted in narrower electroluminescence (EL) spectrum. The device structure of ITO/PEDOT: PSS/MEH-PPV-POSS: 25 wt% CdS0.75Se0.25/Ca (40 nm)/Al demonstrated the best performance with a brightness of 8672 cd/m 2 at 10 V, current efficiency of 2.5 cd/A at 8 V, and an EQE of 0.55% at 150 mA/cm2 .