Synthesis of NIR-Emitting Semiconductor Nanoparticles in a Continuous Flow Reactor
Christoph Gimmler a, Daniel Ness a, Jan Niehaus a, Katharina Poulsen a, Horst Weller b
a CAN GmbH, Grindelallee 117, Hamburg, 20146, Germany
Poster, Katharina Poulsen, 017
Publication date: 1st April 2013

Semiconductor nanocrystals show unique energetic, electronic and optical properties which depend tremendously upon their size. Latest reports have focused on lead sulfide - quantum dots (PbS-QDs).[1][2] While macroscopic lead sulfide has a bandgap of 0.37 eV (which corresponds to a wavelength of 3300 nm), synthesized nanocrystals have diameters between 3 to 8 nm and appropriate excitonic peaks from 1000 to 1600 nm. Due to small bandgap energies (0.8 to 1.2 eV) the optoelectronical transitions of PbS nanocrystals cover the near-infrared region. In addition, they absorb the whole wavelength range below 1000 nm and are highly resistant against heating and bleaching. These properties predestine PbS-QD’s to be used for photovoltaic applications and IR-emitters in LED’s.[3][4]

The classical synthetic routes enable the production of particles with proper homogeneous size dispersions, therewith narrow emission bandwidths and quantum yields above 50%.[1][2] However, common hot-injection syntheses show various issues which can be eliminated by passing on to continuous flow systems. These methods minimize concentration- and temperature-gradients during the reaction and offer perfect mixing of the fluids. Due to these points, producing reasonable amounts of oleic acid stabilized PbS (up to kg/year) with narrow size distribution and a high degree of reproducibility is only possible and economically realizable by a continuous flow reactor. In addition these methods increase the laboratory safety as the expose to chemicals can be reduced to a minimum.

Here we will present our progress in synthesizing spherical, monodisperse, highly luminescent PbS-quantum dots by continuous flow methods. We are able to produce particles with an average FWHM (emission peak) of 115 nm (≙142 meV), compared to single particle line widths averages of 100 meV.[5] The regulation of particle growth and properties by varying temperature, flow speed and precursor parameters will be shown. Working with a continuous flow system allows us to synthesize quantum dots from 3 to 8 nmwith an enormous high degree of reproducibility.

Absorption- and Emissionspectra for three PbS-nanoparticles reactor-samples (synthezised on different days with different stock solutions).
[1] Hines, M.A.; Scholes, G.D. Colloidal PbS Nanocrystals with Size-Tunable Near-Infrared Emission: Observation of Post-Synthesis Self-Narrowing of Particle Size Distribution. Adv. Mater., 2003, 15, 1844-1849. [2] Moreels, I.; Justo, Y.; De Geyter, B.; Haustraete, K.; Martins, J.C.; Hens, Z. Size-Tunable, Bright and Stable PbS Quantum Dots: A Surface Chemistry Study. ASC Nano, 2011, 5, 2004-2012. [3] Tang, J.; Kemp, K. W.; Hoogland, S.; Joeng, K. S.; Liu, H.; Levina, L.; Furukawa, M.; Wang. X.; Debnath, R.; Cha, D.; Chou, K. W.; Fischer, A.; Amassian, A.; Asbury, J. B.; Sargent, E.H. Quantum Dot Photovoltaics in the Extreme Quantum Confinement Regime: The Surface-Chemical Origins of Exceptional Air- and Light-Stability. ACS Nano, 2010, 4, 869-878. [4] Rauch, T.; Böberl, M.; Tedde, S. F.; Fürst, J.; Kovalenko, M. V.; Hesser, G.; Lemmer, U.; Heiss, W.; Hayden, O. Near-infrared imaging with quantum-dot-sensitized organic photodiondes. Nature Photonics, 2009, 3, 332-336. [5] Peterson, J. J.; Krauss, T. D. Fluorescence Spectroscopy of Single Lead Sulfide Quantum Dots. Nano Letters, 2006, 6, 3, 510-514.
We use our own and third party cookies for analysing and measuring usage of our website to improve our services. If you continue browsing, we consider accepting its use. You can check our Cookies Policy in which you will also find how to configure your web browser for the use of cookies. More info