Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStacked electrospun polymer nanofiber heterostructures with tailored stimulated emission
110
0
0.0
(
0
)
Authors
Lech Sznitko
Ask ChatGPT about the research
No Arabic abstract
We present stacked organic lasing heterostructures made by different species of light-emitting electrospun fibers, each able to provide optical gain in a specific spectral region. A hierarchical architecture is obtained by conformable layers of fibers with disordered two-dimensional organization and three-dimensional compositional heterogeneity. Lasing polymer fibers are superimposed in layers, showing asymmetric optical behavior from the two sides of the organic heterostructure, and tailored and bichromatic stimulated emission depending on the excitation direction. A marginal role of energy acceptor molecules in determining quenching of high-energy donor species is evidenced by luminescence decay time measurements. These findings show that non-woven stacks of light-emitting electrospun fibers doped with different dyes exhibit critically-suppressed Forster resonance energy transfer, limited at joints between different fiber species. This leads to obtain hybrid materials with mostly physically-separated acceptors and donors, thus largely preventing donor quenching and making much easier to achieve simultaneous lasing from multiple spectral bands. Coherent backscattering experiments are also performed on the system, suggesting the onset of random lasing features. These new organic lasing systems might find application in microfluidic devices where flexible and bidirectional excitation sources are needed, optical sensors, and nanophotonics.
rate research
Read More
Concomitant amplified spontaneous emission (ASE) and Forster resonance energy transfer (FRET) are investigated in electrospun light-emitting fibers. Upon dye-doping with a proper FRET couple system, free-standing fibrous mats exhibit tunable FRET efficiency and, more importantly, tailorable threshold conditions for stimulated emission. In addition, effective scattering of light is found in the fibrous material by measuring the transport mean free path of photons by coherent backscattering experiments. The interplay of ASE and FRET leads to high control in designing optical properties from electrospun fibers, including the occurrence of simultaneous stimulated emission from both donor and acceptor components. All tunable-optical properties are highly interesting in view of applying electrospun light-emitting materials in lightening, display, and sensing technologies.
Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scattering of light in the nanofibrous system are individually analyzed as mechanisms to enhance Raman scattering. The deposition of gold nanorods on the fibers further amplifies Raman signals due to SERS. This study suggests that Raman signals can be finely tuned in intensity and effectively enhanced in nanofiber mats and arrays by properly tailoring the architecture, composition, and light-scattering properties of the complex networks of filaments.
Hybrid polymer-plasmonic nanostructures might combine high enhancement of localized fields from metal nanoparticles with light confinement and long-range transport in subwavelength dielectric structures. Here we report on the complex behavior of fluorophores coupling to Au nanoparticles within polymer nanowires, which features localized metal-enhanced fluorescence (MEF) with unique characteristics compared to conventional structures. The intensification effect when the particle is placed in the organic filaments is remarkably higher with respect to thin films of comparable thickness, thus highlighting a specific, nanowire-related enhancement of MEF effects. A dependence on the confinement volume in the dielectric nanowire is also evidenced, with MEF significantly increasing upon reducing the wire diameter. These findings are rationalized by finite element simulations, predicting a position-dependent enhancement of the quantum yield of fluorophores embedded in the fibers. Calculation of the ensemble-averaged fluorescence enhancement unveils the possibility of strongly enhancing the overall emission intensity for structures with size twice the diameter of the embedded metal particles. These new, hybrid fluorescent systems with localized enhanced emission, as well as the general Nanowire-Intensified MEF effect associated to them, are highly relevant for developing nanoscale light-emitting devices with high efficiency and inter-coupled through nanofiber networks, highly sensitive optical sensors, and novel laser architectures.
We experimentally observe the fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in an epitaxial graphene-on-Si heterostructure under pumping with a 1550-nm, 80-fs pulsed fiber laser beam and probing with the corresponding terahertz (THz) beam generated by and synchronized with the pumping laser. The time-resolved electric-field intensity originating from the coherent terahertz photon emission is electro-optically sampled in total-reflection geometry. The Fourier spectrum from 1.8 to 5.2 THz agrees well the pumping photon spectrum. This result is attributed to amplified emission of THz radiation from the graphene sample stimulated by the THz probe beam, and provides evidence for the occurrence of negative dynamic conductivity in the terahertz spectral range.
Carbon nanofibers (NFs) have been envisioned with broad promising applications, such as nanoscale actuators and energy storage medium. This work reports for the first-time super-elastic tensile characteristics of NFs constructed from a screw dislocation of carbon nanocones (NF-S). The NF-S exhibits three distinct elastic deformation stages under tensile, including an initial homogeneous deformation, delamination, and further stretch of covalent bonds. The delamination process endows the NF-S extraordinary tensile deformation capability, which is not accessible from its counterpart with a normal cup-stacked geometry. The failure of NF-S is governed by the inner edges of the nanocone due to the strain concentration, leading to a common failure force for NF-S with varying geometrical parameters. Strikingly, the delamination process is dominated by the inner radius and the apex angle of the nanocone. For a fixed apex angle, the yielding strain increases remarkably when the inner radius increases, which can exceed 1000%. It is also found that the screw dislocation allows the nanocones flattening and sliding during compression. This study provides a comprehensive understanding on the mechanical properties of NFs as constructed from carbon nanocones, which opens new avenues for novel applications, such as nanoscale actuators.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
