TY - JOUR A1 - Stroyuk, O. A1 - Weigert, Florian A1 - Raevskaya, A. A1 - Spranger, F. A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Gaponik, N. A1 - Zahn, D. R. T. T1 - Inherently broadband photoluminescence in Ag−In−S/ZnS quantum dots observed in ensemble and single-particle studies N2 - We present a series of results that demonstrate that the broadband photoluminescence (PL) of aqueous glutathione-capped Ag−In−S (AIS) nanocrystals (NCs) is an inherent property of each NC, rather than a collective characteristic of an NC ensemble. By analyzing parameters affecting the PL features such as the postsynthesis annealing and the deposition of a passivating ZnS shell, we found no correlation between the spectral width of the PL band of AIS (AIS/ZnS) NCs and the density of the lattice defects. Analysis of the PL spectra of a series of size-selected AIS/ZnS NCs revealed that the PL width of fractionated NCs does not depend on the NC size and size distribution. The PL measurements in a broad temperature window from 320 to 10 K demonstrated that the PL width does not decrease with decreasing temperature as expected for an emission arising from thermally activated detrapping processes. Also, we show that the model of the self-trapped exciton can be versatilely applied to reconstruct the PL spectra of different AIS NCs and can account for the effects typically attributed to variations in defect state energy. Measurements of the PL properties of single AIS/ZnS NCs highlighted the broadband nature of the emission of individual NCs. The presented results show that the broadband PL of ternary NCs most probably does not originate from lattice defects but involves the NC lattice as a whole, and, therefore, by tailoring the NC structure, PL efficiencies as high as those reported for binary cadmium or lead chalcogenide NCs can be potentially reached. KW - Nano KW - Nanomaterial KW - Ternary quantum dots KW - AIS KW - Semiconductor nanocrystal KW - Photoluminescence KW - Mechanism KW - Single particle spectroscopy KW - Quantum yield KW - Photophysics PY - 2019 U6 - https://doi.org/10.1021/acs.jpcc.8b11835 SN - 1932-7447 VL - 123 IS - 4 SP - 2632 EP - 2641 PB - ACS AN - OPUS4-47419 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schneider, Ralf A1 - Weigert, Florian A1 - Lesnyak, V. A1 - Leubner, S. A1 - Lorenz, T. A1 - Behnke, Thomas A1 - Dubavik, A. A1 - Joswig, J.-O. A1 - Resch-Genger, Ute A1 - Gaponik, N. A1 - Eychmüller, A. ED - Resch-Genger, Ute ED - Schneider, Ralf T1 - pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O N2 - The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which – together with alloyed CdₓHg₁₋ₓTe – are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D₂O and compared to the results from previous dilution studies with a set of thiol-capped Cd₁₋ₓHgₓTe SC NCs in D₂O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman’s test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H₂O compared to D₂O, underlining also the role of hydrogen bonding and solvent molecules. KW - Quantum dots KW - Fluorescence KW - Ligand analysis KW - Nano particles PY - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-371253 VL - 18 IS - 28 SP - 19083 EP - 19092 PB - RSC CY - Cambridge AN - OPUS4-37125 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Müller, M. A1 - Kaiser, Martin A1 - Stachowski, G.M. A1 - Resch-Genger, Ute A1 - Gaponik, N. A1 - Eychmüller, A. T1 - Photoluminescence quantum yield and matrix-induced luminescence enhancement of colloidal quantum dots embedded in ionic crystals N2 - The incorporation of colloidal quantum dots (QDs) into solid matrices, especially ionic salts, holds several advantages for industrial applications. Here, we demonstrated via absolute measurements of photoluminescence quantum yields (PL-QY) that the photoluminescence of aqueous CdTe QDs can be considerably increased upon incorporation into a salt matrix with a simple crystallization procedure. Enhancement factors of up to 2.8 and a PL-QY of 50 to 80%, both in NaCl crystals and incorporated in silicone matrices, were reached. The fact that the achievable PL enhancement factors depend strongly on PL-QY of the parent QDs can be described by the change of the dielectric surrounding and the passivation of the QD surface, modifying radiative and nonradiative rate constants. Time-resolved PL measurements revealed noncorrelating PL lifetimes and PL-QY, suggesting that weakly emissive QDs of the ensemble are more affected by the enhancement mechanism, thereby influencing PL-QY and PL lifetime in a different manner. PY - 2014 U6 - https://doi.org/10.1021/cm5009043 SN - 0897-4756 SN - 1520-5002 VL - 26 IS - 10 SP - 3231 EP - 3237 PB - American Chemical Society CY - Washington, DC AN - OPUS4-31074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Leubner, S. A1 - Schneider, Ralf A1 - Dubavik, A. A1 - Hatami, Soheil A1 - Gaponik, N. A1 - Resch-Genger, Ute A1 - Eychmüller, A. T1 - Influence of the stabilizing ligand on the quality, signal-relevant optical properties, and stability of near-infrared emitting Cd1-xHgxTe nanocrystals N2 - Bright and stable near-infrared (NIR) and infrared (IR) emitting chromophores are in high demand for applications in telecommunication, solar cells, security barcodes, and as fluorescent reporters in bioimaging studies. The best choice for wavelengths >750 nm are semiconductor nanocrystals, especially ternary or alloy nanocrystals like CdHgTe, which enable size and composition control of their optical properties. Here, we report on the influence of growth time and surface chemistry on the composition and optical properties of colloidal CdHgTe. Up to now, these are the only NIR and IR emissive quantum dots, which can be synthesized in high quality in water, using a simple one-pot reaction. For this study we utilized and compared three different thiol ligands, thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and glutathione (GSH). Aiming at the rational design of bright NIR- and IR-emissive alloy materials, special emphasis was dedicated to a better understanding of the role of the surface ligand and adsorption–desorption equilibria on the photoluminescence quantum yield and stability. In this respect, dilution and protonation studies were performed. Our results show that with this simple synthetic procedure, strongly fluorescent CdHgTe colloids can be obtained with MPA as stabilizing ligand revealing quantum yields as high as 45% independent of particle concentration. PY - 2014 U6 - https://doi.org/10.1039/c4tc00582a SN - 2050-7526 SN - 2050-7534 VL - 2 IS - 25 SP - 5011 EP - 5018 PB - Royal Soc. of Chemistry CY - Cambridge AN - OPUS4-31073 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Leubner, S. A1 - Hatami, Soheil A1 - Esendemir, Nehir A1 - Lorenz, T. A1 - Joswig, J.-O. A1 - Lesnyak, V. A1 - Recknagel, Sebastian A1 - Gaponik, N. A1 - Resch-Genger, Ute A1 - Eychmüller, A. T1 - Experimental and theoretical investigations of the ligand structure of water-soluble CdTe nanocrystals N2 - The unique optical properties, such as size-tunable absorption and emission, caused semiconductor nanocrystals to attract a great deal of interest for recent technological developments. For the evaluation of semiconductor nanocrystals as new materials for various applications like optoelectronic devices, knowledge of the structure–property relationships is indispensable, but still presents a challenge. Here, we address these challenges for thioglycolic acid-capped CdTe nanocrystals with a focus on the quantification of thiol ligands, identification of the ligand shell structure and their influence on the optical properties of these nanocrystals. We present the use of a simple analytical technique, the Ellman's test, and ICP-OES analysis for the study of the surface chemistry of these nanomaterials. Together with theoretical calculations, the results of these studies show the strong influence of the amount of Cd–thiolates present in the ligand shell on the concentration-dependent emission properties, thereby providing the basis for a better understanding of the chemical nature of the NC–ligand interface. In this context, the present work contributes to the establishment of a clearer picture and better control of the surface chemistry, which will provide the basis for the design of highly emitting nanocrystals and the prediction of their applicability. PY - 2013 U6 - https://doi.org/10.1039/c3dt50802a SN - 1477-9226 SN - 1477-9234 SN - 1364-5447 VL - 42 SP - 12733 EP - 12740 PB - RSC CY - Cambridge AN - OPUS4-29139 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lesnyak, V. A1 - Lutich, A. A1 - Gaponik, N. A1 - Grabolle, Markus A1 - Plotnikov, A. A1 - Resch-Genger, Ute A1 - Eychmüller, A. T1 - One-pot aqueous synthesis of high qualilty near infrared emitting Cd1-xHgxTe nanocrystals N2 - An efficient one-pot aqueous synthesis of alloyed Cd1-xHgxTe nanocrystals (NCs) is realized and the influence of the experimental conditions and of the initial composition of the NCs on their optical properties is discussed. This approach obtains stable NCs with an emission tunable in the red and the near infrared (NIR) spectral regions ranging from 640 to 1600 nm thereby covering the second and third telecommunication windows. The high photoluminescence quantum efficiency (PL QE) of these colloids with values up to 55% for red emitting, and up to 60% for NIR emitting samples is indicative of the excellent quality of the NCs. KW - Aqueous colloidal synthesis KW - Semiconductor nanoparticles KW - Near infrared photoluminescence KW - Quantum efficiency KW - Stability PY - 2009 U6 - https://doi.org/10.1039/b913200g SN - 0959-9428 SN - 1364-5501 VL - 19 SP - 9147 EP - 9152 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-20758 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hatami, Soheil A1 - Würth, Christian A1 - Kaiser, Martin A1 - Leubner, S. A1 - Gabriel, S. A1 - Bahrig, L. A1 - Lesnyak, V. A1 - Pauli, Jutta A1 - Gaponik, N. A1 - Eychmüller, A. A1 - Resch-Genger, Ute T1 - Absolute photoluminescence quantum yields of IR26 and IR-emissive Cd1-xHgxTe and PbS quantum dots - method- and material-inherent challenges N2 - Bright emitters with photoluminescence in the spectral region of 800–1600 nm are increasingly important as optical reporters for molecular imaging, sensing, and telecommunication and as active components in electrooptical and photovoltaic devices. Their rational design is directly linked to suitable methods for the characterization of their signal-relevant properties, especially their photoluminescence quantum yield (Φf). Aiming at the development of bright semiconductor nanocrystals with emission >1000 nm, we designed a new NIR/IR integrating sphere setup for the wavelength region of 600–1600 nm. We assessed the performance of this setup by acquiring the corrected emission spectra and Φf of the organic dyes Itrybe, IR140, and IR26 and several infrared (IR)-emissive Cd1-xHgxTe and PbS semiconductor nanocrystals and comparing them to data obtained with two independently calibrated fluorescence instruments absolutely or relative to previously evaluated reference dyes. Our results highlight special challenges of photoluminescence studies in the IR ranging from solvent absorption to the lack of spectral and intensity standards together with quantum dot-specific challenges like photobrightening and photodarkening and the size-dependent air stability and photostability of differently sized oleate-capped PbS colloids. These effects can be representative of lead chalcogenides. Moreover, we redetermined the Φf of IR26, the most frequently used IR reference dye, to 1.1 × 10-3 in 1,2-dichloroethane DCE with a thorough sample reabsorption and solvent absorption correction. Our results indicate the need for a critical reevaluation of Φf values of IR-emissive nanomaterials and offer guidelines for improved Φf measurements. PY - 2015 U6 - https://doi.org/10.1039/c4nr04608k SN - 2040-3364 SN - 2040-3372 VL - 7 IS - 1 SP - 133 EP - 143 PB - RSC Publ. CY - Cambridge AN - OPUS4-32408 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grabolle, Markus A1 - Spieles, Monika A1 - Lesnyak, V. A1 - Gaponik, N. A1 - Eychmüller, A. A1 - Resch-Genger, Ute T1 - Determination of the fluorescence quantum yield of quantum dots: suitable procedures and achievable uncertainties PY - 2009 U6 - https://doi.org/10.1021/ac900308v SN - 0003-2700 SN - 1520-6882 VL - 81 IS - 15 SP - 6285 EP - 6294 PB - American Chemical Society CY - Washington, DC AN - OPUS4-20272 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Goryacheva, O. A. A1 - Wegner, Karl David A1 - Sobolev, A. M. A1 - Häusler, I. A1 - Gaponik, N. A1 - Gorycheva, I. Y. A1 - Resch-Genger, Ute T1 - Influence of particle architecture on the photoluminescence properties of silica‑coated CdSe core/shell quantum dots N2 - Light-emitting nanoparticles like semiconductor nanocrystals (termed quantum dots, QDs) are promising candidates for biosensing and bioimaging applications based on their bright and stable photoluminescent properties. As high-quality QDs are often synthesized in organic solvents, strategies needed to be developed to render them water-dispersible without affecting their optical properties and prevent changes in postmodification steps like the biofunctionalization with antibodies or DNA. Despite a large number of studies on suitable surface modification procedures, the preparation of water-soluble QDs for nanobiotechnology applications still presents a challenge. To highlight the advantages of surface silanization, we systematically explored the influence of the core/multishell architecture of CdSe/CdS/ZnS QDs and the silanization conditions on the optical properties of the resulting silanized QDs. Our results show that the optical properties of silica-coated CdSe/CdS/ZnS QDs are best preserved in the presence of a thick CdS (6 monolayers (ML)) intermediate shell, providing a high photoluminescence quantum yield (PL QY), and a relatively thick ZnS (4.5 ML) external shell, effectively shielding the QDs from the chemical changes during silica coating. In addition to the QD core/shell architecture, other critical parameters of the silica-coating process, that can have an influence on the optical properties of the QD, include the choice of the surfactant and its concentration used for silica coating. The highest PL QY of about 46% was obtained by a microemulsion silica-coating procedure with the surfactant Brij L4, making these water-dispersible QDs to wellsuited optical reporters in future applications like fluorescence immunoassays, biomedicine, and bioimaging. KW - Nano KW - Nanomaterial KW - Particle KW - Semiconductor KW - Quantum do KW - Photoluminescence KW - Photophysics KW - Lifetime KW - Sensor KW - Mechanism KW - Surface KW - Shell KW - Silica KW - Silanization KW - Synthesis PY - 2022 U6 - https://doi.org/10.1007/s00216-022-04005-7 SP - 1 EP - 13 PB - Springer AN - OPUS4-54546 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -