Efficient active waveguiding properties of Mo₆ nano-cluster-doped polymer nanotubes

We investigate 1D nanostructures based on a Mo₆@SU8 hybrid nanocomposite in which photoluminescent Mo₆ clusters are embedded in the photosensitive SU8 resist. Tens of micrometers long Mo₆@SU8-based tubular nanostructures were fabricated by the wetting template method, enabling the control of the inner and outer diameter to about 190 nm and 240 nm respectively, as supported by structural and optical characterizations. The image plane optical study of these nanotubes under optical pumping highlights the efficient waveguiding phenomenon of the red luminescence emitted by the clusters. Moreover, the wave vector distribution in the Fourier plane determined by leakage radiation microscopy gives additional features of the emission and waveguiding. First, the anisotropic red luminescence of the whole system can be attributed to the guided mode along the nanotube. Then, a low-loss propagation behavior is evidenced in the Mo₆@SU8-based nanotubes. This result contrasts with the weaker waveguiding signature in the case of UV210-based nanotubes embedding PFO (poly(9,9-di-n-octylfluorenyl-2,7-diyl)). It is attributed to the strong reabsorption phenomenon, owing to overlapping between absorption and emission bands in the semi-conducting conjugated polymer PFO. These results make this Mo₆@SU8 original class of nanocomposite a promising candidate as nanosources for submicronic photonic integration. (paper)