Random lasing from a nanoparticle-based metal–dielectric–dye medium

Waveguide random laser based on a disordered ZnSe-nanosheets arrangement

A waveguide scheme is constructed by coating the matrix of randomly distributed ZnSe nanosheet structures with a layer of dye-doped polymer, which provides strong feedback or gain channels for the emission from the dye molecules and enables successful running of a random laser with FWHM of ~0.65 nm. The strong scattering by the nanostructures and the strong confinement provided by the active waveguide layer are the key essentials for the narrow-band and low-threshold operation of this random laser. The random laser scheme reveals an obvious two-threshold behavior, which is corresponding to the thresholds of TM and TE modes. The feedback mechanisms for laser action are investigated by power Fourier transforming of the spectra. This kind of active waveguide not only provides high quality confinement of the radiation for efficient amplification, but also enables possible directional output of this kind of random laser.

The fabrication of periodic polymer/silver nanoparticle structures: in situ reduction of silver nanoparticles from precursor spatially distributed in polymer using holographic exposure

A new approach to producing volume periodic polymer-metal nanoparticle structures is presented. Periodic distribution of Ag nanoparticles in a polymer film can be obtained by applying the holographic patterning in the UV or visible spectral range to the composite material comprising photocurable monomers, photoinitiators and a solution of silver nitrate in acetonitrile. Photopolymerization of the composite in the interference pattern provides formation of a highly efficient volume grating composed of periodic polymer regions and Ag precursor-containing regions. Subsequent homogeneous UV irradiation and/or thermo-treatment of the grating causes reduction of silver ions to Ag nanoparticles in the areas of the film containing the metal precursor. Spectroscopic measurements confirm the formation of the nanoparticles in the gratings. Transmission electron microscopy showed a regular spatial distribution of well-defined Ag nanoparticles in a polymer film with a periodicity governed by the geometry of holographic structuring. The average diameter of nanoparticles can be controlled by the wavelength and intensity of holographic exposure as well as the composite formulation. A possible mechanism of silver nanoparticle formation by free radicals as reducing agents is presented.