3-D rare earth-doped colloidal photonic crystals

Photoluminescence from rare-earth ions confined to a photonic bandgap structure may exhibit interesting spectral modifications such as narrowing, broadening or intensity enhancement [1,2], all of potential use in a future generation of optoelectronic devices. Three-dimensional photonic crystals have been synthesized by a colloidal/sol-gel route, starting with the self-organization of polystyrene microspheres into artificial opal structures by vertical convective self-assembly, followed by sol-gel infiltration of the interstices with silica or titania sols doped with 0.75% Er and 2.5-5% Yb, by dip-coating and the removal of the polymeric template by heat treatment [3,4]. The structural and optical properties of the opals and inverse opals prepared by this method have been studied by scanning electron microscopy (SEM) and near infrared spectroscopy to assess the relationship between structure and the photonic properties obtained. The SEM images show the quality of the crystals, which in most cases contained ordered domains of the order of ? 100 ?m2, on the average. Variable incidence reflectivity spectra have been measured for the polystyrene opals, silica / titania infiltrated opals and silica / titania inverse opals. The positions of the angle resolved stop bands have been compared with simulations using the transfer matrix method; the stop band shoulders exhibited for reflection angles above 45º off-normal incidence, previously attributed to Bragg reflection from non-compact planes [5,6], were shown to be measurement artefacts. The colloidal photonic crystals prepared have been optically characterized based on effective medium descriptions and their properties have been compared with predictions from theoretical simulations. Photoluminescence measurements performed included the emission spectra of Er3+ ions near 1.5 ?m and Yb3+ ions near 1 ?m, plus the corresponding lifetimes and these spectral results have been compared with those characteristic of the same dopant ions in bulk silica or titania material in the absence of a photonic bandgap structure. References [1] R.M. Almeida, A.C. Marques and S. Portal, Opt. Mat. 27, 1718-1725 (2005). [2] R.M. Almeida, A.C. Marques, A. Chiasera, A. Chiappini and M. Ferrari, J. Non-Cryst. Solids 353, 490-493 (2007). [3] R.M. Almeida and S. Portal, Current Opinion in Sol. State and Mater. Sci. 7, 151-157 (2003). [4] R.M. Almeida, M.C. Gonçalves and S. Portal, J. Non-Cryst. Solids 345&346, 562-569 (2004). [5] S.G. Romanov, C.M. Sotomayor Torres, M. Egen and R. Zentel, Phot. Nanostr. Fundam. Appl. 4, 59-68 (2006). [6] M.V. Rybin, A.V. Baryshev, M. Inoue, A.A. Kaplyanskii, V. Kosobukin, M.F. Limonov, A.K. Samusev and A.V. Sel'kin, Phot. Nanostr. Fundam. Appl. 4, 146-154 (2006).