OPTICAL PROPERTIES OF POLYSTYRENE OPALS INFILTRATED WITH CYANINE DYES IN THE FORM OF J-AGGREGATES
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OPTICAL PROPERTIES OF POLYSTYRENE OPALS INFILTRATED WITH CYANINE DYES IN THE FORM OF J-AGGREGATES F. Marabelli1, D. Comoretto2, D. Bajoni1, M. Galli1, and L. Fornasari1 1 INFM-Dipartimento di Fisica “A. Volta”, Università degli Studi di Pavia, via Bassi 6, 27100Pavia (Italy) 2 INFM-Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova, via Dodecaneso 31, 16146-Genova (Italy) ABSTRACT We report preliminary data on the infiltration of polystyrene opals with cyanine dye water solutions, which are known to form J-aggregates. Different approaches are used to infiltrate cyanines inside opals. The degree of infiltration is evaluated by scanning and transmission electron microscopy as well as micro reflectance spectroscopy. Data show that in spite of the low wettability of polystyrene with water solutions, some infiltration can be achieved. Even though this degree of infiltration is still not enough to observe strong modification on the photonic band structures, further strategies to improve it are in progress.
INTRODUCTION Photonic crystals are materials having a periodical and regular modulation of the dielectric constant. This modulation can be achieved in one, two or three dimensions giving rise to different structures, which control the propagation of the electromagnetic waves [1]. Among three dimensional structures, artificial direct- and inverse- opals have been extensively studied [2] due to the relatively easy growth techniques, which makes them the prototype model for the investigation of fundamental physical properties of 3D photonic crystals [3]. More recently, the possibility to modulate the photonic properties of such photonic crystals by infiltration with photoactive materials has attracted a deep attention [4]. The modulation of optical properties of silica opals upon infiltration with organic dyes [5, 6] and inorganic materials [7] was recently reported. However, as far as we know, few data are reported on the infiltration of polystyrene opals. As a matter of fact, the infiltration process must satisfy different requirements: the solvent for the photoactive molecules must be a non solvent for polystyrene spheres. Moreover, wettability of opal surface by this liquid may prevent the infiltration process. In this case, specific strategies must be developed. In spite of these problems, since high quality polystyrene opals can be grown, and organic molecules possess high linear and nonlinear polarizability useful to be combined with photonic crystal properties, the investigation of the infiltration with conjugated dyes is appealing since it allows to prepare full organic three dimensional infiltrated photonic crystals. Recently, we have grown high quality polystyrene opals, which allowed the investigation of new physical phenomena related to their photonic band structure [8]. Now, we extend our work to the infiltration process. Aim of this work is to report our preliminary results on the infiltration of polystyrene opals with carbocyanine, which may form, in the suitable con
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