JO URNAL O F T O R T HE EUR O PEAN O PTI CAL SOCI ETY R APID PUBLICATI O NS Journal of the European Optical Society - Rapid Publications 4, 09032 (2009) www.jeos.org Tuning optical properties of opal photonic crystals by structural defects engineering F. Di Stasio Dipartimento di Chimica e Chimica Industriale, Universit` a degli Studi di Genova, via Dodecaneso 31, 16146 Genova (Italy) M. Cucini Dipartimento di Chimica e Chimica Industriale, Universit` a degli Studi di Genova, via Dodecaneso 31, 16146 Genova (Italy) L. Berti Dipartimento di Chimica e Chimica Industriale, Universit` a degli Studi di Genova, via Dodecaneso 31, 16146 Genova (Italy) D. Comoretto comorett@chimica.unige.it Dipartimento di Chimica e Chimica Industriale, Universit` a degli Studi di Genova, via Dodecaneso 31, 16146 Genova (Italy) A. Abbotto Dipartimento di Scienza dei Materiali e INSTM, Universit` a di Milano-Bicocca, via Cozzi 53, 20125 Milano (Italy) L. Bellotto Dipartimento di Scienza dei Materiali e INSTM, Universit` a di Milano-Bicocca, via Cozzi 53, 20125 Milano (Italy) N. Manfredi Dipartimento di Scienza dei Materiali e INSTM, Universit` a di Milano-Bicocca, via Cozzi 53, 20125 Milano (Italy) C. Marinzi Dipartimento di Scienza dei Materiali e INSTM, Universit` a di Milano-Bicocca, via Cozzi 53, 20125 Milano (Italy) We report on the preparation and optical characterization of three dimensional colloidal photonic crystal (PhC) containing an engineered planar defect embedding photoactive push-pull dyes. Free standing polystyrene films having thickness between 0.6 and 3 μm doped with different dipolar chromophores were prepared. These films were sandwiched between two artificial opals creating a PhC structure with planar defect. The system was characterized by reflectance at normal incidence angle (R), variable angle transmittance (T) and photoluminescence spectroscopy (PL) Evidence of defect states were observed in T and R spectra which allow the light to propagate for selected frequencies within the pseudogap (stop band). [DOI: 10.2971/jeos.2009.09032] Keywords: photonic crystals, dipolar chromophores, artificial opals 1 INTRODUCTION Among PhC, i.e. materials possessing a periodic modulation of the dielectric constant on a length scale comparable to the wavelength of visible light, artificial opals are a simple and cheap playground to investigate optical effects [1, 2]. As a matter of fact, while traditional growth methods to prepare three dimensional PhC, like lithographic techniques, are time and energy consuming, self-assembly of building blocks like microspheres in the case of opals [3]–[11] is an interesting al- ternative process based on the spontaneous growth of stable well-defined structures, starting from elements which interact through non covalent bonds through quasi equilibrium steps, which intrinsically might repel defects. This technique is also scalable to wafer substrate and silicon technology [12]–[14]. The main drawback still remaining with opals is that their structure does not allow the formation of a complete pho- tonic band gap (PBG). Only the inverse opal structure with the proper dielectric contrast allow opening a complete PBG [9]. Moreover, some care have to be used during the opal growth in order to reduce the role of possible defects like stacking faults [15]–[18]. In spite of these limitations, the advantages in the production of opals and their versatility to be engineered even in patterned substrates [19, 20] allows to simply test new ideas and concepts. As already exploited in semiconductors technology, modula- tions and engineering of their properties is a key point. The main features of PhC depend on their structure and dielec- tric contrast [21]. Being the opal structure well defined (face centred cubic) with a unit cell length depending on sphere diameter, the main possibility to tune their properties is the modulation of the refractive index of composing materials. This approach has been widely exploited by several research groups by infiltrating into opal interstices a variety of materi- als ranging from metals, nanoparticles, inorganic and organic semiconductors (for a review of this fields see [22] and ref- erences therein). We exploited and investigated this latter ef- fect by infiltrating opals with gold nanoparticles [23]–[25] and molecular [26] or polymeric semiconductors [27]. It should be noted that the use of organic chromophores as active materials for infiltration is rather unusual [28]–[36] and, when present, mostly limited to commercial dyes without a proper engineer- ing of novel systems. Received December 11, 2008; published June 14, 2009 ISSN 1990-2573