Dr. rer. nat. Stefan Kirstein

Dr. Kirstein erforscht derzeit die optischen und strukturellen Eigenschaften von hybriden Nanomaterialien, insbesondere die Kopplung von zweidimensionalen Materialien (wie Molybdändisulfid und Wolframsulfid) mit organischen Farbstoffen und Quantenpunkten. Im Fokus steht dabei die Energieübertragung zwischen diesen unterschiedlichen Komponenten, um die Lichtemission zu verstärken und für optoelektronische Anwendungen nutzbar zu machen. Ein aktuelles Projekt adressiert modulare, biopolymerbasierte Wasserfiltration zur Schwermetallentfernung. Seine Methoden kombinieren hochauflösende Mikroskopie, Spektroskopie und theoretische Modellierung, um Nanohybride gezielt zu charakterisieren und zu optimieren. Die Arbeiten sind relevant für Optoelektronik, Sensorik, Photonik und Umwelttechnik.

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• SFB 448 III: Hybridaggregate: Struktur und Energieleitung (Teilprojekt C 6)

  Quelle ↗

  Förderer: DFG Sonderforschungsbereich Zeitraum: 01/2004 - 12/2009 Projektleitung: Dr. rer. nat. Stefan Kirstein

• Entwicklung eines Gerätes zur Untersuchung sub-mikroskopischer Partikel

  Quelle ↗

  Zeitraum: 04/2006 - 03/2007 Projektleitung: Dr. rer. nat. Stefan Kirstein

• SFB 951/3: Optische Anregung von TMDC/Farbstoff-Hybriden unter mechanischer Beanspruchung (TP A06)

  Quelle ↗

  Förderer: DFG Sonderforschungsbereich Zeitraum: 07/2019 - 06/2023 Projektleitung: Dr. rer. nat. Stefan Kirstein, Prof. Dr. rer. nat. Jürgen P. Rabe

• Strongly Photoluminescent CdTe Nanocrystals by Proper Surface Modification

  1998

  The Journal of Physical Chemistry B · DOI

  CdTe nanoclusters were prepared in aqueous solution by the reaction between Cd 2+ and NaHTe in the presence of thioglycolic acid. Under reflux, the clusters start to crystallize and show a narrow band emission. The photoluminescence efficiency of CdTe nanocrystals strongly depends on the pH value of the colloidal solution. The maximum quantum yield at room temperature is approximately 18% when the pH value of the CdTe solution is brought to 4.5 by using thioglycolic acid. The optical spectroscopy studies imply that the pH-dependent behavior of the CdTe nanocrystals' fluorescence is caused by structural changes on the surface rather than the size of the nanocrystals. Systematic absorption and fluorescence studies on dialyzed samples suggest that in the acidic range a shell of cadmium thiol complexes is formed around the CdTe core. Thus, the fluorescence quantum yield is enhanced dramatically when the solution is made acidic. In contrast, such a shell can also be produced in the alkaline range, but only after the CdTe nanocrystal crude solution is purified by dialysis.

• Electroluminescence of different colors from polycation/CdTe nanocrystal self-assembled films

  2000

  Journal of Applied Physics · DOI

  Water soluble thiol capped CdTe nanocrystals are assembled into ultrathin films in combination with poly(diallyldimethylammonium chloride) (PDDA) by the self-assembly method of layer-by-layer adsorption of oppositely charged polyelectrolytes. Electroluminescent devices, which produce different color emissions, are fabricated by sandwiching CdTe/PDDA films between indium–tin–oxide (ITO) and aluminum electrodes using CdTe nanocrystals of different sizes. It is shown that the electroluminescence (EL) spectra of the CdTe/polymer films are nearly identical to the photoluminescence spectra of the corresponding CdTe nanocrystals in aqueous solutions. The devices produce room-light visible light output with an external quantum efficiency up to 0.1%. Light emission is observed at current densities of 10 mA/cm2 and at low onset voltages of 2.5–3.5 V, which depends on the thickness of the film indicating field-dependent current injection. A variation of the EL efficiency with the size of the CdTe particles is observed and explained by the size dependent shift of the CdTe energy levels with respect to the work function of the electron injecting Al electrode. This is confirmed by the behavior of two-layer devices prepared from two differently sized CdTe particles being spatially separated, i.e., one size CdTe near ITO and the other size CdTe near Al by using the self-assembly method.