Multiple Scattering from Electrospun Nanofibers with Embedded Silver Nanoparticles of Tunable Shape for Random Lasers and White-Light-Emitting Diodes.

Random lasers (RLs) are convenient, tunable, and widely applicable. However, the influence of fluorescence lifetime on the scattering and nanofiber distribution of nanofibers with various shapes of silver nanoparticles (Ag NPs) embedded within is unclear. We prepared poly(vinyl alcohol) (PVA) nanofibers with Ag NPs through electrospinning (ES) and pyrromethene 597 dye doping. We determined the influences of the particles on scattering enhancement and localized surface plasmon resonance (LSPR) in RLs. The distinct scattering rates and LSPR can be used to control optical properties for sensing devices and other applications. Compared with traditional films, the threshold of the nanofibers with Ag NPs is 35% lower. In addition to improved matching between the LSPR and emission spectra, enhanced coupling of the electric field with nonradiative energy amplifies the radiative emission. Furthermore, the luminescence lifetime shortened by increasing the scattering rate. An excessive scattering rate may accelerate radiative recombination and convert some recombination into nonradiative recombination to produce a more sensitive device. Finally, we applied the prepared nanofibers to a backlight display and fabricated a white-light-emitting diode (LED) with a distinct thickness of nanofibers. The fabricated device is suitable for application in other LEDs and RL devices.

Novel Multifunctional Luminescent Electrospun Fluorescent Nanofiber Chemosensor-Filters and Their Versatile Sensing of pH, Temperature, and Metal Ions.

Novel multifunctional fluorescent chemosensors composed of electrospun (ES) nanofibers with high sensitivity toward pH, mercury ions (Hg2+), and temperature were prepared from poly(N-Isopropylacrylamide-co-N-methylolacrylamide-co-rhodamine derivative) (poly(NIPAAm-co-NMA-co-RhBN2AM)) by employing an electrospinning process. NIPAAm and NMA moieties provide hydrophilic and thermo-responsive properties (absorption of Hg2+ in aqueous solutions), and chemical cross-linking sites (stabilization of the fibrous structure in aqueous solutions), respectively. The fluorescent probe, RhBN2AM is highly sensitive toward pH and Hg2+. The synthesis of poly(NIPAAm-co-NMA-co-RhBN2AM) with different compositions was carried on via free-radical polymerization. ES nanofibers prepared from sensory copolymers with a 71.1:28.4:0.5 NIPAAm:NMA:RhBN2AM ratio (P3 ES nanofibers) exhibited significant color change from non-fluorescent to red fluorescence while sensing pH (the λPL, max exhibited a 4.8-fold enhancement) or Hg2+ (at a constant Hg2+ concentration (10-3 M), the λPL, max of P3-fibers exhibited 4.7-fold enhancement), and high reversibility of on/off switchable fluorescence emission at least five times when Hg2+ and ethylenediaminetetraacetic acid (EDTA) were sequentially added. The P3 ES nanofibrous membranes had a higher surface-to-volume ratio to enhance their performance than did the corresponding thin films. In addition, the fluorescence emission of P3 ES nanofibrous membranes exhibited second enhancement above the lower critical solution temperature. Thus, the ES nanofibrous membranes prepared from P3 with on/off switchable capacity and thermo-responsive characteristics can be used as a multifunctional sensory device for specific heavy transition metal (HTM) in aqueous solutions.