199 research outputs found

    Luminescence in sulfides : a rich history and a bright future

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    Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles

    Ultrafast exciton dephasing in PbS colloidal quantum dots

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    In this work, we have measured the ground state excitonic dephasing in PbS QDs of sizes from 3.7nm to 5.7nm diameter in the temperature range from 5K to 100K by transient degenerate four-wave mixing (FWM) using 100fs pulses. A combination of heterodyne and k-selection detection was implemented to increase sensitivity and enable 4 orders of magnitude dynamic range in the FWM field detection

    Colloidal semiconductor quantum dots : from synthesis to photonic applications

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    In this research project we synthesized colloidal semiconductor nanocrystals, more specifically PbS and PbSe quantum dots (Qdots) with a typical diameter of 2-10nm, using wet chemical techniques. These materials are promising for telecom applications, as their band gap depends on the particle size and is tunable over the entire near-infrared spectral range. The main aim of the project was to investigate whether the high nonlinear refractive index can be used in photonic devices on a silicon platform. The colloidal Qdot synthesis typically produces a suspension of particles, stabilized by organic ligands. Understanding the nature and dynamics of this ligand shell is essential for a further processing of the Qdots, and it was studied with nuclear magnetic resonance spectroscopy. Next, we developed methods to quantify the linear optical properties of the Qdots. This knowledge helped us to determine and comprehend the nonlinear refractive index. A comparison of the results with typical semiconductors, such as Si and AlGaAs, showed that the Qdots are efficient nonlinear materials. Hereafter, the application-oriented research was initiated by covering a Silicon-on-Insulator microring with a Qdot doped polymer film and investigating the linear transmission characteristics of this hybrid device. A clear interaction between the Qdots and the light in the ring was observed, and the transmission spectrum was strongly influenced by the Qdot size and concentration. A nonlinear study on the microrings is currently under development; preliminary results are already presented

    New materials for nonlinear optical applications : the nonlinear refractive index of colloidal PbSe quantum dots

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    We present a detailed study of the nonlinear optical properties of colloidal PbSe quantum dot (Q-PbSe) suspensions and thin films. The nonlinear refractive index n2 has been measured with the Z-scan technique as a function of wavelength (1.20 -- 1.75 textmum), optical intensity and nanocrystal volume fraction. The n2-spectra show negative resonances near the Q-PbSe optical transitions. We attributed the high n2 to biexciton creation within the Q-PbSe. The n2 of a close-packed thin Q-PbSe film is 6 orders of magnitude larger than values for bulk Si of GaAs at telecom wavelengths, suggesting that Q-PbSe might be a promising material for all optical signal processing.info:eu-repo/semantics/publishe

    Revisiting the anion framework conservation in cation exchange processes

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    We investigated the effect of cation exchange on the anionic framework of lightly doped CdSe:Te/CdS nanorods. In contrast with previously studied core/shell systems, the Te dopant, located in the center of the CdSe core, provides an extremely sensitive indicator for any structural changes of the anionic framework that may occur as a result of the cation exchange process. We first optimized the cation exchange procedure in order to retain the fluorescence properties of the CdSe:Te/CdS nanorods after exchange of Cd2+ for Cu+ and back to Cd2+. Next, using multiexciton spectroscopy, we were able to probe the magnitude of the exciton exciton repulsion interaction and use that to assess the degree of crystal structure conservation. Our findings provide a much stronger proof that the anion framework is indeed rigid, showing no evidence of significant migration of the anionic dopant

    Efficient charge transfer in solution-processed PbS quantum dot–reduced graphene oxide hybrid materials

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    We developed a general approach to couple silane-functionalized rGO with colloidal semiconductor nanocrystals, which show efficient and tunable charge transfer
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