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The problem of the electronic excitation energy transfer in liquids and solids is among the basic ones in condensed matter physics [1,2]. Understanding of the energy transfer processes is important since they represent the intermediate step between the act of excitation and the process where the electron energy is put to use. The energy transfer can be mediated by quasiparticles or by the electromagnetic field. The lat ter process was first described by Förster [3]. He con sidered the energy transfer caused by weak dipoledipole interaction between the donor and acceptor, the process called fluorescence resonance energy transfer (FRET). Later Dexter [4] generalized Förster's theory for the case of higher multipole and exchange interactions. The further development of the Förster-Dexter theory involved the inclusion of vari ous complicating factors and determination of its validity limits [1].Electron excitation energy transfer in nanostruc tures promising for both fundamental physics and applications is currently of main interest. In nano structures, quasiparticles can tunnel through a poten tial barrier of a finite width separating constituent nanoparticles. This process is actively studied both theoretically and experimentally [5][6][7][8][9]. The Förster-Dexter energy transfer between quantum dots (QDs) was analyzed theoretically in [10] and investigated experimentally in [11][12][13][14][15]. A decrease in the photolu minescence (PL) intensity and an increase in the PL decay rate were observed for the QDs acting as donors, and an increase in the PL intensity was observed for the QDs acting as acceptors. It was shown that the effi ciency of the energy transfer between the QDs can be fairly high, exceeding 50%, and depends on the spac ing between the QDs. When the spacing is larger than about 10 nm, the energy transfer between the QDs no longer takes place.The properties of composite structures consisting of carbon nanotubes (CNTs) and QDs have been actively investigated in recent years. These structures are interesting as a playground for studying novel phys ical phenomena. Furthermore, they will possibly find numerous applications, e.g., in optoelectronics, pho togalvanics, and photovoltaics [16,17]. One of the main topics in the studies of such composite structures is the energy transfer between the two constituents, of which one can act as the donor and the other as the acceptor.Here, we study experimentally the electronic exci tation energy transfer between cadmium sulfide QDs and CNTs.To study energy transfer, samples with CdS QDs deposited onto a CNT layer were fabricated in the fol lowing way. Arrays of vertically oriented CNTs on sin gle crystalline Si(100) substrates were synthesized by chemical decomposition of a toluene/ferrocene reac tive mixture at 820°C as described in [18]. Cadmium sulfide QDs deposited onto CNTs were synthesized by the Langmuir-Blodgett method [19]. In order to pas sivate the surface and increase the PL intensity of the QDs, they were annealed in an ammonia atmosphere at 200°C [...

Photoluminescence (PL) properties of CdS nanoparticles were studied depending on spacing between the nanoparticles and carbon nanotube (CNT) surface. Using a chemical bath deposition procedure the nanoparticles were grown directly on CNT arrays or arrays covered by a polystyrene layer. The polymer thickness was changed by varying the polystyrene concentration in a solution and the duration of CNT immersing. Transmission electron microscopy and atomic force microscopy were used for estimation of CdS nanoparticle size. An increase in the separation between CdS and CNTs was found to enhance the PL intensity and contribute to the exciton lifetime.PL spectra of CdS nanoparticles grown on a CNT surface and polystyrene layer coating the CNTs.

The crystal structure and shape of the CdS quantum dots (QDs) obtained by the Langmuir−Blodgett method were studied by transmission electron microscopy, extended X-ray absorption fine structure spectroscopy (EXAFS), and ultraviolet spectroscopy. X-ray photoelectron spectroscopy (XPS) and stationary photoluminescence spectroscopy (PL) methods were used to determine the dominant surface defects. Initially synthesized QDs within the Langmuir−Blodgett film of fatty behenic acid have a cubic structure and oblate spheroid shape, while free-standing QDs obtained after the matrix evaporation have a wurtzite structure and sphere-like shape. QDs within the matrix demonstrate a wide PL band centered at 2.3 eV corresponding to defect-assisted radiative recombination; after the matrix annealing and passivation of the QD surface in an ammonia atmosphere, the PL spectrum demonstrates a high-intensity band-edge peak together with a low-intensity defect-assisted shoulder. It was established that sulfur (V S ) vacancies are the dominating defects. A model of simultaneous band-edge and defect-assisted recombination through the V S level was proposed.