Optical Characterization of Cadmium Telluride Doped Heterostructured Opaline Photonic Crystal
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Optical Characterization of Cadmium Telluride Doped Heterostructured Opaline Photonic Crystal V. G. Solovyev, S.G. Romanov, C.M. Sotomayor Torres, N. Gaponik*, A. Eychmüller* & A. L. Rogach* Institute of Materials Science and Dept. of Electrical and Information Engineering, University of Wuppertal, Gauss-str. 20, 42097 Wuppertal, Germany *Institute of Physical Chemistry, University of Hamburg, Bundesstr. 45, 20146, Hamburg, Germany ABSTRACT A double-layer photonic crystal (PhC) possessing incomplete photonic band gap (PBG) has been prepared by successive formation of one opaline film on top of another and subsequent impregnation with CdTe colloidal nanocrystals as the light source. Transmission, reflection and photoluminescence (PL) spectra of this nanocomposite have been measured from 1.8 to 2.5 eV at different angles of the light incidence and detection. The suppression of emission intensity has been found at both stop bands of the PhC heterostructure. Depending on the excitation power, either suppression or enhancement of the emission rate at the stop band has been observed. INTRODUCTION The development of PBG materials towards functional devices for waveguiding and light emission requires their intentional internal structuring. In the case of opaline materials the complexity of this task is related to the necessity of combining the macroscale structuring with the self-organized growth of the PhC. The feasibility of this approach was first demonstrated with a PhC based on bulk opal [1] and then confirmed with thin film opals [2]. In spite of the still unidentified role of the heterointerface in optical properties of the PhC, the overall optical transmission/reflectance of multilayered opals can be represented as the linear superposition of stop bands of individual layers. With respect to light emission, the suppression of the emission from opaline PhC is known as the less robust characteristic of the PhC [3], which is very sensitive to the peculiarities of the PBG. Moreover, the most desirable feature of the PBG material, namely, the suppression/enhancement of the emission rate has not yet been unambiguously demonstrated in the case of opals. It seems reasonable to expect that co-existence of different PBG structures in a single piece of material will enrich the variety of emission phenomena. PhC heterostructures were designed to incorporate an artificial defect in the body of the opal and this double-layered opaline film can be considered as a pre-requisite to realize such structures. So far, light diffraction in PhC heterostructures has been studied. In this work we examine the effect of multiple stop bands upon the emission properties of the light source embedded in heterostructure. Correspondingly, we compare the propagation of an external light inside the crystals with the emission generated internally.
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MATERIAL PREPARATION AND EXPERIMENTAL TECHNIQIES The samples under study were double-layer opaline films made of latex beads with sphere diameters ~ 240nm and ~270 nm for the “top” and “bottom” laye
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