Ilkem Ozge Huyal

Selective enhancement of surface-state emission and simultaneous quenching of interband transition in white-luminophor CdS nanocrystals using localized plasmon coupling

We propose and demonstrate the controlled modification and selec- tive enhancement of surface-state emission in white-luminophor CdS nanocrys- tals (NCs) by plasmon-coupling them with proximal metal nanostructures. By carefully designing nano-Ag films to match their localized plasmon resonance spectrally with the surface-state emission peak of CdS NCs, we experimen- tally show that the surface-state emission is substantially enhanced in the visible wavelength, while the interband (band-edge) transition at the shorter wavelength far away from the plasmon resonance is simultaneously significantly suppressed. With such plasmon tuning and consequent strong plasmon coupling specifi- cally for the surface-state transitions, the surface-state emission is made stronger than the band-edge emission. This corresponds to an enhancement factor of 12.7-fold in the ratio of the surface-state peak emission to the band-edge peak emission of the plasmon-coupled film sample compared with that in solution. Such a plasmonic engineering of surface-state emission in trap-rich CdS white nanoluminophors holds great promise for future solid-state lighting.

White light generation tuned by dual hybridization of nanocrystals and conjugated polymers

Dual hybridization of highly fluorescent conjugated polymers and highly luminescent nanocrystals (NCs) is developed and demonstrated in multiple combinations for controlled white light generation with high color rendering index (CRI) (> 80) for the first time. The generated white light is tuned using layer-by-layer assembly of CdSe/ZnS core-shell NCs closely packed on polyfluorene, hybridized on near-UV emitting nitride-based light emitting diodes (LEDs). The design, synthesis, growth, fabrication and characterization of these hybrid inorganic?organic white LEDs are presented. The following experimental realizations are reported: (i) layer-by-layer hybridization of yellow NCs (?PL=580?nm) and blue polyfluorene (?PL=439?nm) with tristimulus coordinates of (x, y)=(0.31, 0.27), correlated color temperature of Tc=6962?K and CRI of Ra=53.4; (ii) layer-by-layer assembly of yellow and green NCs (?PL=580 and 540?nm) and blue polyfluorene (?PL=439?nm) with (x, y)=(0.23, 0.30), Tc=14395?K and Ra=65.7; and (iii) layer-by-layer deposition of yellow, green and red NCs (?PL=580, 540 and 620?nm) and blue polyfluorene (?PL=439?nm) with (x, y)=(0.38, 0.39), Tc=4052?K and Ra= 83.0. The CRI is demonstrated to be well controlled and significantly improved by increasing multi-chromaticity of the NC and polymer emitters.

Quantum efficiency enhancement in film by making nanoparticles of polyfluorene

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.

White emitting polyfluorene functionalized with azide hybridized on near-UV light emitting diode for high color rendering index

We develop and demonstrate high-quality white light generation that relies on the use of a single-type simple conjugated polymer of polyfluorene functionalized with azide groups (PFA) integrated on a near-UV LED platform. The high-quality white emission from the polyfluorene is achieved by using the azide functionalization to facilitate cross-linking intentionally when cast into solid-state form. Hybridized on n-UV InGaN/GaN LED at 378 nm, the PFA emitters collectively generate a very broad down-converting photoluminescence at longer wavelengths across the entirety of the visible spectrum, yielding high color rendering indices up to 91.

High-Quality White Light Generation using Dually Hybridized Nanocrystals and Conjugated Polymers

Hybridizing different sizes of CdSe/ZnS core-shell nanocrystal emitters layer by layer with highly fluorescent polyfluorene as conjugated polymer on n-UV InGaN/GaN LEDs, we achieved high-quality white light with color rendering index > 80, fulfilling the future solid state lighting requirement. Here we also demonstrated the ability to tune the white light properties as desired by carefully designing and realizing the hybrid device parameters including the type and film thickness of closely-packed NC emitters, the concentration and film thickness of polymer emitters, and the order of NC and polymer films. Given their high light quality and tunable optical properties, these hybrid organic-inorganic white light sources provide a high potential for future lighting and display applications.

Plasmon enhanced colloidal nanocrystal composites incorporating Au nanoparticles in a repeating layered architecture

In summary, we presented plasmonic high-efficiency Au-CdTe nanocomposite films in a three-dimensional construction of repeating layers. These composites integrate Au nanoparticles at a fixed optimal dielectric spacing and plasmon-couple them with CdTe nanocrystal emitters for significantly enhanced emission. In the Au-CdTe nanocomposite film, we showed that the emission of CdTe NCs is increased by 4.37 fold and the quantum efficiency is increased by 43%, reaching a high level of 30% in film. This proof-of-concept demonstration of plasmonic AuCdTe nanocomposite films opens a new direction for the development of future NC-based optoelectronic devices.

Surface-state emission enhancement in white-luminophor CdS nanocrystals using localized plasmon coupling

To make surface-state emission stronger than band-edge emission for the first time, we proposed and demonstrated plasmon coupling of the surface-state emission from the traps in these CdS nano-luminophors using localized plasmons.

Optically active bi-polymer hetero-nanoparticles

In summary, preparing four different bi-polymer nanoparticle systems we investigated the energy transfer dynamics between the donor PF and the acceptor MEH-PPV. The highest level of energy transfer efficiency is obtained to be 35% for (MEH-PPV/PF) sequential hetero-NPs, which are demonstrated for the first time in this work. These bipolymer nanostructures hold great promise for tunable white-light generating systems with optimized tristimulus coordinates, CCTs, and CRIs.

Increased quantum efficiency and reduced red-shift in polymer nanoparticle luminophors

In this paper, using a polyfluorene derivative, increased fluorescence quantum efficiency and reduced red-shift in the film form of polymer nanoparticle luminophors is achieved, when compared to directly spin coated polymer thin films.

White Light Generation with Azide Functionalized Polyfluorene Hybridized on Near-UV Light Emitting Diode

We present white light generation using poly[(9,9-dihexylfluorene)-co-alt-(9,9-bis-(6- azidohexyl)fluorene] (PFA) for the first time. Hybridizing PFA on near-UV LED, we demonstrate high color rendering index up to 91.0.