Fan Kong

Tailoring light emission properties of organic emitter by coupling to resonance-tuned silver nanoantenna arrays

A convenient nanotechnique is reported to tailor the light emission properties of organic emitter poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) by coupling to resonance-tuned silver nanoantenna arrays. It is revealed experimentally and theoretically that the enhanced photoluminescence from the MEH-PPV/silver nanoantenna complex may originate from the energy transfer effect in the surface plasmon resonance coupling between the MEH-PPV and silver nanocaps and from local electromagnetic field enhancement of nanogaps between the silver nanocaps in the background of the light-emitting MEH-PPV. The results are corroborated by the finite difference time domain simulation results.

Silver nanovoid arrays for surface-enhanced Raman scattering.

Highly ordered silver nanovoid arrays are fabricated on porous anodic alumina membranes to produce robust and cost-efficient surface-enhanced Raman scattering (SERS) substrates. Plasmonic tunability can be accomplished by adjusting the topography with different anode voltages. Evenly distributed plasmonic fields, high average enhancement factor, and excellent ambient stability due to the natural protective layer are some of the unique advantages, and the silver nanovoid arrays are applicable to sensing devices.

Optical emission from the aggregated state in poly [2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene]

We report the photoluminescence characteristics of solid solutions of poly[2-methox-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) with different concentrations in polystyrene. Reduction in the distances between the MEH-PPV chains with increased MEH-PPV concentrations makes the conjugation segments aggregated in the solid solution. Absorption by the conjugation segments in the aggregated state leads to a redshift absorption edge. By comparing the photoluminescence and absorption spectra of the solid solutions with those of the 100% MEH-PPV film, it is shown that the emission from the 100% MEH-PPV film originates from the radiative recombination of excitons in the aggregated state.

Modulation of surface-enhanced Raman spectra by depth selective excitation of embedded indium tin oxide nanoisland arrays

Embedded transparent conducting indium tin oxide (ITO) nanoisland arrays were prepared by pulsed laser deposition of ITO films on roughened Si templates and post-annealing to investigate the surface-enhanced Raman scattering activities. Considerable Raman enhancement of a rhodamine 6G probe during Ar+ laser excitation was observed and modulated by the thickness of the ITO film due to the exponentially decaying field of the localized surface plasmon polaritons at the interface. Because the Raman-enhancing functional layer is protected at the ITO/Si interface, this system is reusable and also believed to be immune to contamination and other surface activities.

Effect of absorption to nanopore on optical properties of conjugated polymers in porous anode alumina

The optical properties of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) in the nanopores of porous anodic alumina (PAA) are investigated using temperature-dependent photoluminescence (PL) spectra. The PL spectrum of MEH-PPV in PAA becomes wide because the polymer chains absorb to the nanopore walls to restrict excitation energy transfer. Unlike the MEH-PPV film, the PL peak wavelength of MEH-PPV in PAA is independent of temperature in the range of 80 to 290 K. The influence of temperature on the emission bandwidth of MEH-PPV in the nanopores is obviously less than that in the film because temperature-dependent inhomogeneous broadening is suppressed by the absorption effect.

Band-gap-dependent emissions from conjugated polymers coupled silver nanocap array

The optical properties of poly(2,5-dioctyloxy-p-phenylene) (PPP) and poly[3-(2,5,8-trioxanonyl) thiophene] (P3TT) coupled silver nanocap array have been investigated. The absorption spectrum of P3TT and the emission spectrum of PPP match the absorption of the silver nanocap array. Plasmon energy transfer occurs from the silver nanocap array to P3TT or from PPP to the silver nanocap array, resulting in the largely increased or decreased photoluminescence (PL), respectively. The PL enhancement of the P3TT coupled silver nanocap array is more than 9-fold; whereas the PL intensity of the PPP coupled silver nanocap array is less than one-tenth of the PPP film.

Interaction between indium tin oxide nanoparticles and cytochrome c: A surface-enhanced Raman scattering and absorption spectroscopic study

Indium-tin-oxide (ITO) nanoparticles were annealed in vacuum or reducing atmosphere to obtain different surface structures and investigate their influence on the adsorptive character and conformation of cytochrome c (Cyt c) molecule. Annealing-induced morphometric or structural changes of ITO nanoparticles were characterized by instruments of transmission electron microscopy, x-ray diffraction, and Raman scattering. Semiconductor ITO nanoparticle-enhanced Raman scattering of Cyt c was observed and the enhanced efficiency was found to closely depend on the surface structures which control the adsorbance of buffer anions needed for Cyt c loading. Direct electron transfer between Cyt c and ITO surface at the moment of molecular elastic collision was found and a reverse electron transfer process for O-terminated surface and metal-terminated surface was observed, according to absorption spectroscopic measurement on the residual solution.

Modulating emission from acceptor in donor-acceptor diblock copolymers by plasmon resonance energy transfer

We have investigated the optical properties of all-conjugated block copolymers, poly (2,5-dioctyloxy-p-phenylene)-b-poly[3-(2,5,8-trioxanonyl) thiophene] (PPP-b-P3TT), coupled silver nanocap array. The photoluminescence (PL) enhancement of the acceptor is increased with the mole fraction of the P3TT block in the coupled copolymer. The emission from the PPP blocks and the absorption of the P3TT blocks match the plasmon resonance frequency of the silver nanocap array. The emission from the PPP blocks is absorbed by the silver nanocap array to propagate surface plasmons or surface plasmon polaritons near the interfaces of the conjugated polymer/silver nanocap array, whose energies can be transferred to the P3TT blocks. As a result, more than 14-fold PL enhancement of the P3TT blocks has been observed in the coupled copolymer by photoexcitation at the absorption maximum of the PPP blocks.

The effect of imide substituents on the optical properties of perylene diimide derivatives

As one of the most important organic semiconductors, perylene diimide derivatives (PDIs) have been widely applied in optoelectronics. Two kinds of soluble PDIs with different imide substituents have been synthesized and their optical properties have been investigated. The photoluminescence (PL) intensity of the PDI with amino phenyl imide substituents (NH2 -PDI) is much lower than that of the PDI with octyl imide substituents (O-PDI). It can be found that the Stokes shift of O-PDI is positive, whereas, the Stokes shift of NH2 -PDI is negative. The emission intensity of the 0-0 electron transition relative to that of the 1-0 electron transition (I0-0 /I1-0 ) in the PL spectrum of O-PDI is decreased, but the value of I0-0 /I1-0 in the PL spectra of NH2 -PDI is increased as the dielectric constant of the solvent increases. The large overlap between the absorption and PL spectra plays an important role to result in the low PL intensity of NH2 -PDI. The PL decay data show that a non-radiative process, photoinduced electron transfer, also contributes to the low PL intensity of NH2 -PDI. The results can help researchers to understand the effect of the imide substituents on the optical properties of PDIs.

Enhanced emission from the acceptor in all-conjugated diblock copolymers due to spatial effect of nanopores

We have investigated the emission properties of all-conjugated diblock copolymers, poly(2,5-dioctyloxy-p-phenylene)-b-poly[3-(2,5,8-trioxanonyl)thiophene] (PPP-b-P3TT), in the nanopores of porous anodic alumina membrane. In contrast with the copolymer solution and film, the relative intensity of the emission from the P3TT blocks in the copolymer in the nanopores is largely increased for excitation at the absorption maximum of the PPP blocks. Different from the copolymer film, the relative photoluminescence (PL) intensity of the P3TT blocks is obviously increased with the increase of the P3TT blocks in the copolymers in the nanopores. The separated copolymer chains and the efficient resonance energy transfer caused by spatial limit contribute to higher relative PL intensity of the P3TT blocks in the copolymers in the nanopores than those in the solutions and films.