Hybrid organic/inorganic semiconductor nanostructures with highly efficient energy transfer Diana Savateeva, a Dzmitry Melnikau, b Vladimir Lesnyak, c Nikolai Gaponik c and Yury P. Rakovich * ad Received 14th February 2012, Accepted 21st March 2012 DOI: 10.1039/c2jm30917c Using electro-static assembly of complementary organic (cyanine dye) and inorganic (quantum dots) building blocks we report on formation of an advanced nanohybrid system with highly efficient nonradiative energy transfer properties. In contrast to previous approaches, formation of J-aggregates in cyanine dye solution was triggered by direct injection of as-synthesized colloidal CdTe quantum dots without any additional surface treatment. The optical properties of formed hybrid aggregates have been investigated by absorption and photoluminescence spectroscopy and fluorescence lifetime imaging microscopy. A quantum dot/J-aggregate system shows the enhanced absorption in visible and ultraviolet parts of the spectrum typical of quantum dots, along with the narrow emission linewidth and fast recombination rate characteristic of the J-band emitters. These quantum dot/J-aggregate hybrid systems may have applications in light harvesting systems with the extended spectral absorption as well as optical sensors and optoelectronic devices. Introduction Design of nanoscale systems with specified structure and targeted properties is one of the key goals in modern nanotechnology. In this respect the integration of organic and inorganic materials at the nanoscale offers the possibility of developing new types of functional hybrid materials and nanodevices with unique optical, electrical and photophysical properties, which can be very different from those of their constituent parts. A main challenge in this field is the ability to fabricate high quality nanostructures in the simplest and most reliable way. Particularly interesting for such applications is recently proposed new class of nanohybrid structures consisting of semiconductor nanocrystals and organic dye molecules in the J-aggregate state. 1 J-aggregates, originally discovered by Jelley 2 and Scheibe, 3 are one-dimensional molecular arrangements in which the transition moments of the individual dye molecules are aligned parallel to the line joining their centers. J-aggregates exhibit a sharp char- acteristic absorption peak, the so-called J-band, which is red- shifted in respect to the monomer absorption band due to the delocalization of excitation over an aggregate by intermolecular interaction between transition dipole moments. 4 Due to the delocalized nature of the excitonic excitations, J-aggregates have the narrowest absorption and luminescence bands among organic materials, large oscillator strengths and giant third-order nonlinear susceptibility. Formation of J-aggregates in highly concentrated dye aqueous solutions can be triggered by salts, metal ions, surfactants as well as by a variety of macromolecules, such as polyelectrolytes, gelatine, albumins, proteins, RNA and DNA. 5,6 Semiconductor nanocrystals, otherwise known as quantum dots (QDs), are promising for a number of applications because of their size-dependent optical properties. 7 They have wide absorption bands and relatively narrow, tunable emissions, which makes them ideal candidates as F€ orster resonance energy transfer (FRET) pairs. The shell of ligand molecules surrounding the QDs allows their chemical properties to be adjusted through relatively straightforward solution-based surface chemistry. 8 On the basis of their versatility and unique optical properties, semiconductor nanocrystals are impacting now the areas of photonics, 9,10 electronics, 11 bio-imaging 12 and energy conversion. 13 In this work we studied optical properties of a novel type of hybrid structures that combine CdTe QDs with organic dye molecules (pseudoisocyanine iodide (PIC)) in a J-aggregate state. We demonstrated that formation of J-aggregates in an aqueous solution of cationic cyanine dye can be induced by direct injec- tion of as-synthesized QDs carrying a negative surface charge without the need for any further surface functionalization. Due to electrostatic interaction these ionic species form hybrid organic/inorganic structures, in which the optical energy har- vested by the QDs as nano-antennas then transferred to J-aggregates. The extremely thin (0.5 nm) surface ligand shell a Centro de Fisica de Materiales (MPC, CSIC-UPV/EHU) and Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 5, Donostia-San Sebastian, 20018, Spain b CIC nanoGUNE Consolider, Tolosa Hiribidea 76, Donostia-San Sebastian, 20018, Spain c Physical Chemistry, TU Dresden, Bergstrasse 66b, Dresden, D-01062, Germany d IKERBASQUE, Basque Foundation for Science, Bilbao, 48011, Spain. E-mail: yury.rakovich@ehu.es 10816 | J. Mater. Chem., 2012, 22, 10816–10820 This journal is ª The Royal Society of Chemistry 2012 Dynamic Article Links C < Journal of Materials Chemistry Cite this: J. Mater. Chem., 2012, 22, 10816 www.rsc.org/materials PAPER Downloaded by UNIVERSIDAD DEL PAIS VASCO on 14 May 2012 Published on 22 March 2012 on http://pubs.rsc.org | doi:10.1039/C2JM30917C View Online / Journal Homepage / Table of Contents for this issue