Browsing by Subject "Energy-transfer"

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    Bifunctional highly fluorescent hollow porous microspheres made of BaMoO4: Pr3+ nanocrystals via a template-free synthesis
    (The Royal Society of Chemistry, 2011) Yang, X.; Zhou, Y.; Yu, X.; Demir, Hilmi Volkan; Sun, X. W.
    We report a bifunctional hollow porous microsphere composed of single-component BaMoO4 : Pr3+ nanocrystals by a facile template-free synthesis. All the as-synthesized hollow microspheres are well-dispersed with a diameter of 2-4 mu m and the BaMoO4 : Pr3+ nanocrystals measure 30-60 nm in diameter. It is observed that there are a large amount of pores with an average diameter is 17.5 nm in the shell of these BaMoO4 : Pr3+ hollow microspheres, thereby exhibiting a great promise for drug delivery. Meanwhile, the strong, narrow-bandwidth red emission centered at 643 nm from these nanostructures can be efficiently excited from 430 nm to 500 nm. The combination of excellent luminescent properties and a hollow porous nanostructure suggest a great promise in the application of these nanostructures in lighting and displays, and in biomedicine such as targeted drug delivery, integrated imaging, diagnosis, and therapeutics. In addition, the template-free solution synthesis can be applied to the design and fabrication of other functional architectures.
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    Chromogenic and fluorogenic sensing of biological thiols in aqueous solutions using BODIPY-based reagents
    (American Chemical Society, 2013) Isik, M.; Ozdemir, T.; Turan, I. S.; Kolemen, S.; Akkaya, E. U.
    Judicious design of BODIPY dyes carrying nitroethenyl substituents in conjugation with the BODIPY core yields dyes that respond to biological thiols by both absorbance and emission changes. Incorporation of solubilizing ethyleneglycol units ensures water solubility. The result is bright signaling of biologically relevant thiols in the longer wavelength region of the visible spectrum and in aqueous solutions.
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    Hyperbolic metamaterials based on quantum-dot plasmon resonator nanocomposites
    (Optical Society of America, 2014) Zhokovsky, S. V.; Ozel, T.; Mutlugun, E.; Gaponik, N.; Eychmuller, A.; Lavrinenko, A. V.; Demir, Hilmi Volkan; Gaponenko, S. V.
    We theoretically demonstrate that nanocomposites made of colloidal semiconductor quantum dot monolayers placed between metal nanoparticle monolayers can function as multilayer hyperbolic metamaterials. Depending on the thickness of the spacer between the quantum dot and nanoparticle layers, the effective permittivity tensor of the nanocomposite is shown to become indefinite, resulting in increased photonic density of states and strong enhancement of quantum dot luminescence. This explains the results of recent experiments [T. Ozel et al., ACS Nano 5, 1328 (2011)] and confirms that hyperbolic metamaterials are capable of increasing the radiative decay rate of emission centers inside them. The proposed theoretical framework can also be used to design quantum-dot/nanoplasmonic composites with optimized luminescence enhancement. (C) 2014 Optical Society of America
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    Observation of efficient transfer from Mott-Wannier to Frenkel excitons in a hybrid semiconductor quantum dot-polymer composite at room temperature
    (American Institute of Physics, 2010-12-29) Nizamoglu, S.; Sun, X. W.; Demir, Hilmi Volkan
    Efficient conversion from Mott-Wannier to Frenkel excitons is observed at room temperature. The time-resolved photoluminescence shows that the energy transfer rate and efficiency reach 0.262 ns-1 and 80.9%, respectively. The energy transfer is enabled by strong dipole-dipole coupling in a hybrid inorganic/organic system of CdSe/ZnS core/shell heteronanocrystal and poly[2-methoxy-5-(3,7-dimethyl-octyloxy)-1,4-phenylenevinylene] homopolymer composite, and the measured energy transfer efficiencies are consistent with the analytical model.
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    Quantum efficiency enhancement in film by making nanoparticles of polyfluorene
    (Optical Society of America, 2008) Huyal, I. O.; Ozel, T.; Tuncel, D.; Demir, Hilmi Volkan
    We report on conjugated polymer nanoparticles of polyfluorene that were formed to exhibit higher fluorescence quantum efficiency in film (68%) and reduce undesired emission peak wavelength shifts in film (by 20 nm), compared to the solid-state polymer thin film made directly out of the same polymer solution without forming nanoparticles. Using the facile reprecipitation method, solutions of poly[9,9-dihexyl-9H-fluorene] in THF were added at different volume ratios to obtain different size distributions of nanoparticle dispersions in water. This allowed us to control the sizedependent optical emission of our polyfluorene nanoparticles. Such organic nanoparticles hold great promise for use as efficient emitters in optoelectronic device applications. (C) 2008 Optical Society of America.