Self-assembled Photonic Crystals

Three-dimensional ordered photonic crystals have been fabricated on solid substrates with a self-assembling method starting from a suspension of dye-doped polymeric nanospheres in water. These photonic crystals showed angle-dependent stop band for light transmission and, correspondingly, Bragg reflection peak due to the photonic crystal lattice. Polystyrene nanoparticles of 306 nm and 288 nm diameter, respectively in the case of the Rhodamine B and Fluored dye, were used to obtain self-assembled photonic crystals. They show 40% reflectance at 610 nm for Rhodamine B and 35% reflectance at 574 nm for Fluored doped materials.

The size of the spheres calculated by Bragg’s law are in good agreement with those evaluated by scanning electron microscopy (SEM). The appropriate choice of sphere diameters results in an overlap between the photonic stop-band and the dye emission spectrum. The photonic crystals showed angle-dependent suppression of spontaneous emission of the dye in the wavelength range of the photonic stop band and enhancement near the band edge. In reflection geometries, spectral narrowing and directional emission, all indicative of stimulated emission, were observed from the active photonic crystal matrix. The results of laser induced emission studies on the dye doped photonic crystals are presented.

Microribbons based on PMMA@EY nanoparticles have been fabricated by room temperature self-assembly of aqueous colloidal suspension on highly wettable glass substrates. Surface chemical treatment assisted the formation of long (up to few centimeters) regular ribbons with rectangular section. Lateral size and height of the structures have been controlled by changing the suspension concentration and/or the deposition volume: the higher suspension concentration produces larger and thicker ribbons and the higher deposited volume produces thicker ribbons (up to 23 µm with 198 µL of a 3 wt % suspension). Moreover, a transition from a film-like to a ribbon-like growth has been observed with increasing nanoparticles concentration. Short range ordering and photonic crystal features have been maintained in the fluorescent ribbon microarchitecture, resulting in a self-assembled material with excellent potential for the development of mirror-less and random lasers.

 

References

1) A.Yadav, R. De Angelis, M. Casalboni, F. De Matteis, P. Prosposito, F. Nanni, I. Cacciotti
Spectral properties of self-assembled polystyrene nanospheres photonic crystals doped with luminescent dyes
Opt. Mater., 35, 1538-1543 (2013). 

2) R. De Angelis , I. Venditti, I. Fratoddi, F. De Matteis, P. Prosposito, I. Cacciotti, L. D'Amico, F. Nanni, A.Yadav, M. Casalboni , M. V Russo
From nanospheres to microribbons: self-assembled Eosin Y doped PMMA nanoparticles as photonic crystals
J. Colloid Interface Sci.,  414 24-32 (2014).