To preserve the morphological properties of para-hexaphenyl (p-6P) based nano- bers and simultaneously tune their emission wavelength, periodic organic-organic hetero-epitaxy was utilized. Multilayer structures of p-6P and -sexithiophene (6T) have been prepared by hot wall epitaxy and analyzed by scanning force microscopy, uorescence microscopy, X-ray di raction and time resolved spectroscopy. We demonstrate that organic heteroepitaxy can be applied to produce multilayered nano- bers with high crystallinity, well de ned epitaxial relationships along di erent material phases, molecular azimuthal order, and long-range morphological homogeneity. It is shown, that it is possible to precisely control and tune the highly polarized photoluminescence emission of the nano- bers from the blue to the green and orange spectral regime by a variation of the 6T concentration. Remarkably, it is possible to prepare nano- bers emitting white polarized light.
We report waveguide amplification of spontaneous emission and coherent random laser action in individual self-assembled organic nanofibers grown by high-vacuum deposition. The interpretation of the experimental results is given on the basis of simple models, including transfer matrix calculations in one-dimensionally disordered structures. We present also the numerical results for light scattering from a nanofiber which can be used as a basis for further experiments.
Systematic investigations of luminescence lifetimes of organic phenylene nanofibers are presented as a function of intrinsic parameters such as morphology or bleaching factor as well as extrinsic parameters such as substrate material, coating or excitation intensity. By varying either one of these parameters, the decay times of the electronic excitation can be varied. This should have a strong influence on the efficiency of nanolasing, which is observed by increasing the excitation intensity of a femtosecond pump laser. Lasing action starts at pump fluences as low as a few <i>μ</i>J/cm<sup>2</sup> per pulse. In ensemble measurements, the number of lasing modes depends strongly on the density of contributing nanofibers. In spatially resolved measurements, the nonlinear optical response of individual nanofibers is investigated. This enables us to make a correlation between the morphological features of the nanofibers, as deduced from atomic-force microscopy, and their lasing properties.