WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Book Part Control of the Particle Size and Purity of Nano Zinc Oxide(Taylor & Francis, 2014) Özmıhçı Ömürlü, Filiz; Balköse, DevrimEffects of template, mechanical mixing and/or ultrasound mixing on the size of the ZnO crystals obtained by precipitation at 30 °C from aqueous zinc chloride and potassium hydroxide solutions were investigated by 2k factorial design. Precipitation method is employed to synthesize nano zinc oxide particles. Monodisperse nano ZnO having 29 nm particle size was produced by adding triethyl amine and applying simultaneously mechanical and ultrasound mixing. The surface area and the density of the powder were 21 m2/g and 4.8 g/cm3. It contains 5.2% impurities present as CO3-2 and bound OH- groups. Volumetric resistivity was found as 1.3 × 107ohm cm. Absorption spectrum of the powder showed absorption peak at 353 nm. The room temperature fluorescence spectrum of the powder revealed a strong and sharp UV emission band at 391 nm due to free exciton or bound exciton of ZnO and a weak and broad violet emission band at 405 nm due to zinc vacancies.Article Citation - WoS: 46Citation - Scopus: 50Investigation of Europium Concentration Dependence on the Luminescent Properties of Borogermanate Glasses(Elsevier Ltd., 2017) Gökçe, Melis; Şentürk, Ufuk; Uslu, Deniz K.; Burgaz, Gözde; Şahin, Yüksel; Gökçe, Aytaç GürhanIn order to elucidate the effect of europium content on the optical and luminescent properties of borogermanate glasses, a series of Eu3+ doped 30B2O3-40GeO2-(30-x)Gd2O3 glasses with various doping levels (x=1–9 mol%) have been synthesized and studied with transmission, absorption, photoluminescence and decay time measurements. The transmission spectra proved that the title glasses maintained a high transparency about 80% in the 440 to 900 nm region. Based on the absorption spectra, the optical band gaps obtained from Tauc's plot can be narrowed by increasing content of Eu3+. From the photoluminescence spectra, the strongest red emission has been observed from the 5D0→7F2 level of Eu3+ ions in borogermanate glasses. The strongest emission and excitation intensities of Eu3+ ions are at the doping level of x=7 mol% and then these intensities decrease due to concentration quenching. The red to orange ratio (R/O) of 5D0→7F2 to 5D0→7F1 transitions has been investigated to predict the local environment of Eu3+ ions. Judd-Ofelt (J-O) analyses have been performed from the emission spectra. The values of R/O and Ω2 present an increase with increasing doping level, indicating the lower symmetric environment for Eu3+ ions and higher covalency for Eu-O bond. The emission efficiency calculated from J-O theory is 75% at x=2 mol%. The decay time curves of 6P7/2→8S7/2 transition of Gd3+ ions and 5D0–7F2 transition of Eu3+ ions confirm the energy transfer from Gd3+ to Eu3+ ions.Article Citation - WoS: 2Citation - Scopus: 2The Effect of Thickness of Silver Thin Film on Structural and Optical Properties of Porous Silicon(World Scientific Publishing Co. Pte Ltd, 2017) Çetinel, A.; Özdoğan, M.; Utlu, G.; Artunç, N.; Şahin, G.; Tarhan, EnverIn this study, porous silicon (PS) samples were prepared on n-type silicon (100) wafers by electrochemical etching method, varying the current density from 20 to 100mA/cm2 and keeping constant HF concentration (10%) and etching time of 15min. Then, Ag thin films, which have 10, 50 and 100nm film thicknesses, were deposited on PS layers by using thermal evaporation to investigate the influence of Ag film thickness on structural and optical properties of PS. The structural and optical properties of PS and Ag deposited PS layers have been investigated by XRD, FE-SEM, Raman and photoluminescence (PL) spectroscopy. FE-SEM XRD and Raman analyzes indicate that average pore size and porosity of PS layers increase with the increasing current density. Further, Ag nanoparticles have embedded in pore channel. PL measurement reveals that higher porosity of PS would be better to form the Ag-PS nano-composite material leading to stronger PL band. The PL spectra of PS and Ag-PS samples indicate that PL bands show blue shift with increasing current density and film thickness. Consequently, it has been found that the structural and optical properties of PS depend on current density and Ag film thickness individually.Article Citation - WoS: 8Citation - Scopus: 9A New Method To Extend the Stress Response of Triboluminescent Crystals by Using Hydrogels(Elsevier Ltd., 2017) İncel, Anıl; Reddy, Subrayal M.; Demir, Mustafa MuammerPolyacrylamide hydrogel entrapment of EuD4TEA or Cu(NCS)(py)2(PPh3) radically extends the emission time of the triboluminescent (TL) crystalline particles by a factor of 103, optimized when matching the hydrophilic/hydrophobic characteristics of the TL/gel components. Triboluminescence intensity improves with hydration of the TL/hydrogel composite. The composites may be used in impact-related sensor applications.Article Citation - WoS: 8Hydrogen Sulfide Determination by Solid Surface Luminescence(Springer Verlag, 1996) Eroğlu, Ahmet Emin; Volkan, Mürvet; Bayramlı, Erdal; Ataman, O. Yavuz; Mark, Harry B.In the analytical system suggested, atmospheric hydrogen sulfide reacts with the surface of a filter paper treated with aqueous cadmium chloride and yields a luminescent species whose intensity can be correlated with the analyte concentration in ambient air. It was shown that the luminescent species are CdS solid particles which were formed in a well defined size. The paper luminescence was also tried on polymeric surfaces; polyethyleneoxide, polyvinyl alcohol, ethylcellulose and carboxymethylcellulose were found to give a similar luminescence signal. The system can be used on the tip of an optical fiber for an irreversible, cumulative type of analytical device for hydrogen sulfide determination. The 3s detection limit for the paper luminescence detection system was 7.8 ppb H2S.Article Citation - WoS: 26Citation - Scopus: 27Developing a Facile 1 Method for Highly Luminescent Colloidal Cdsxse1_x Ternary Nanoalloys†(Royal Society of Chemistry, 2013) Ünlü, Caner; Ünal Tosun, Gülçin; Sevim, Seçil; Özçelik, SerdarWe report a facile method to synthesize highly luminescent colloidal CdSxSe1 xternary nanoalloys. The synthesis is achieved exactly in one-step, one-pot and at low temperature, by applying the two-phase thermal approach. The optical and structural properties of the nanoalloys were characterized by various techniques. Photoluminescence of the nanoalloys is tunable from 435 to 545 nm by either the size or the composition of the nanoalloys. Highly luminescent nanoalloys having quantum yields up to 90% were prepared. The hydrodynamic size of the nanoalloys can be varied from 1.4 to 10.0 nm by the reaction time. DLS measurements showed that the size distribution of the nanoalloys is monodispersed. TEM images confirmed the size and the size distribution of the nanoalloys. The sulfur fraction in the nanoalloy composition, measured by XRD and verified by EDX, is modulated from 0.17 to 0.95 by increasing the amount of thiourea in the chalcogenide mixture. The sulfur-rich nanoalloys are formed when the initial mole ratio of the chalcogenide (S : Se) is equal or higher than eleven-fold. The gradient and homogeneous internal structures are revealed by analysis of the alloy composition as a function of the growth time. We propose that the two-phase approach, a non-injection technique, is a facile and versatile method to develop highly luminescent CdSxSe1 x nanoalloys without an inorganic coating layer.