Light filter tailoring - the impact of light emitting diode irradiation on the morphology and optical properties of silver nanoparticles within polyethylenimine thin films

In this contribution in situ emission filter generation for, e.g. fluorescence light detection by morphology tailoring of silver nanoparticles within a polymer layer, is presented for the first time. After depositing a pretreated film of polyethylenimine containing spherical silver nanoparticles the composite layer was irradiated with green LEDs (peak wavelength 530 nm). This leads to a morphology change of the silver nanoparticles and therefore to a change in absorption properties of the resulting polymer film with an absorption maximum at 550 nm. This tailoring of silver nanoparticles embedded in a transparent polymer matrix could address many novel applications such as adaptable light filters for future lab-on-a-chip applications. A LED for fluorescence light excitation was used to illuminate the silver nanoparticles, which led to an increasing absorption of that particular light spectrum, and therefore in situ produced a fluorescence emission filter. The effect of the treatment time, the silver ion concentration, and the temperature at which the light-shaping was done was studied. The silver nanoparticles were investigated using UV/Vis-spectroscopy and scanning electron microscopy. The observed nanoparticle shapes give reasons for a novel hypothesis of nanoparticle evolution. The forced plasmon oscillation seems to cause excited regions at the silver nanoparticles where adsorbed silver ions are preferably photoreduced. This results in the possibility of tailoring the morphology and therefore the optical properties of the growing nanoparticles.