TY - JOUR A1 - Hirsch, A. A1 - Lohmann, S.-H. A1 - Strelow, C. A1 - Kipp, T. A1 - Würth, Christian A1 - Geißler, Daniel A1 - Komoski, A. A1 - Wolter, C. A1 - Weller, H. A1 - Resch-Genger, Ute A1 - Mews, A. T1 - Fluorescence Quantum Yield and Single-Particle Emission of CdSe N2 - The fluorescence quantum yield (QY) of CdSe dot/CdS rod (DR) nanoparticle ensembles is dependent on the Shell growth and excitation wavelength. We analyze the origin of this dependency by comparing the optical properties of DR ensembles to the results obtained in single-particle experiments. On the Ensemble level, we find that the QY of DRs with shell lengths shorter than 40 nm exhibits no dependence on the excitation wavelength, whereas for DRs with shell lengths longer than 50 nm, the QY significantly decreases for excitation above the CdS band gap. Upon excitation in the CdSe core, the ensemble QY, the fluorescence wavelength, and the fluorescence blinking behavior of individual particles are only dependent on the radial CdS shell thickness and not on the CDs shell length. If the photogenerated excitons can reach the CdSe core region, the fluorescence properties will be dependent only on the surface passivation in close vicinity to the CdSe core. The change in QY upon excitation above the band gap of CdS for longer DRs cannot be explained by nonradiative particles because the ratio of emitting DRs is found to be independent of the DR length. We propose a model after which the decrease in QY for longer CdS shells is due to an increasing fraction of nonradiative exciton recombination within the elongated shell. This is supported by an effective-mass-approximation-based calculation, which suggests an optimum length of DRs of about 40 nm, to combine the benefit of high CdS absorption cross section with a high fluorescence QY. KW - Fluorescence KW - Quantum dot KW - Photophysics KW - Single particle spectroscopy KW - Mechanism KW - Theory KW - Ensemble measurements KW - Quantum yield KW - CdSe KW - CdS shell PY - 2019 DO - https://doi.org/10.1021/acs.jpcc.9b07957 VL - 123 IS - 39 SP - 24338 EP - 24346 PB - ACS Publications AN - OPUS4-49556 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 DO - 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 -