Localized nanoclusters formation in PDMS upon irradiation with femtosecond laser

We demonstrate formation of localized carbonaceous and siliconaceous clusters, confined to the modified region on a micron scale, when PDMS (polydimethylsiloxane) is irradiated by intense femtosecond pulses. Micro-Raman studies also suggest formation of quasi-crystalline silicon nano-clusters whose size varies with the incident laser fluence. The modified region produces broad photoluminescence whose intensity increases with laser fluence. We observed red-edge excitation effect in PDMS wherein the fluorescence from the laser modified region shifts to longer wavelengths as the excitation wavelength is increased to the red edge of the absorption band. Excitation spectra reveal four distinct absorption bands that contribute to the emission from the laser-modified region, two each ascribed to carbonaceous and siliconaceous clusters.