Denise Williams

Participant: PROMISE AGEP Research Symposium


Denise N. Williams

Department: Chemistry and Biochemistry

Institution: University of Maryland Baltimore County (UMBC)



Synthesis and Environmental Studies of CdSe/ZnS and ZnSe/ZnS Quantum Dots

Denise Williams1, Sunipa Pramanik2, Christy Haynes2, and Zeev Rosenzweig1

  1. University of Maryland Baltimore County, Department of Chemistry and Biochemistry, Baltimore, MD 21250
  2. University of Minnesota, Department of Chemistry, Minneapolis, MN 55455

This presentation describes the synthesis, characterization, and environmental impact of luminescent CdSe/ZnS and ZnSe/ZnS quantum dots (QD). Cadmium-containing QD, such as CdSe/ZnS, are commonly used because of their superior optical properties in comparison to other material QD. More recently though, cadmium-free alternatives, such as ZnSe/ZnS QD, are becoming more attractive because they lack this known toxic element which should inevitable reduce the environmental impact of QD. The synthesis of the CdSe/ZnS and ZnSe/ZnS systems are similar colloidal processes, differing only in the use of dopants for the ZnSe/ZnS QD to cause the emission profile to mirror that of the CdSe/ZnS QD. The material characterization of these QD involves analysis of brightness, polydispersity, lifetime, chemical stability, and photostability using absorbance, fluorescence, and mass spectrometry techniques. With the anticipation that cadmium-free QD may replace cadmium-containing QDs in a wide range of applications, the environmental impact of the two systems is modeled in this study with the organism Shewanella oneidensis MR-1. These studies have validated the hypothesis that the ZnSe/ZnS QD can be significantly less toxic than their cadmium alternative, while allowing for an optically comparable technology.



Denise N. Williams is a second year graduate student at the University of Maryland, Baltimore County (UMBC) as a member of Dr. Zeev Rosenzweig’s research group. With this group, she studies the synthesis, characterization and environmental impact of optically active quantum dots. Denise is currently a National Science Foundation AGEP Fellow, a Meyerhoff Graduate Fellow, and a research member of the Center for Sustainable Nanotechnology. Prior to her time at UMBC, Denise earned a Bachelor of Science in Chemistry and a Bachelor of Science in Forensic Science from the University of New Haven in West Haven, Connecticut in May 2015.



Denise Williams’ current research focuses on the synthesis and characterization of luminescent ZnSe/ZnS quantum dots in an effort to replace toxic cadmium-containing nanomaterials, like CdSe/ZnS quantum dots. She has begun synthesizing and comparing the chemical and optical properties and toxic effects of ZnSe/ZnS to CdSe/ZnS. The synthesis conditions of the two systems are similar, so the comparison is relatively straightforward. Both systems have size tunability for absorbance and emission, but CdSe/ZnSe has a wider range of possible emission wavelengths. For the ZnSe/ZnS system Denise have begun doping with manganese ions in order to give a wider range of emission. Lanthanide metal doping is the anticipated next step on this front. The properties of lifetime and quantum yield are also under investigation. For study of the ‘toxic’ effect she has collaborations, through the Center of Nanotechnology, with those working with Shewanella, Nematodes, and Drosphila organisms. They have received batches of ZnSe, ZnSe/ZnS, CdSe, CdSe/ZnS, and Mn:ZnSe/ZnSe for relative organismal lysis assays upon quantum dot exposure. So far, data from Shewanella assays have shown significantly lower lysis from the ZnSe/ZnS systems compared to the CdSe/ZnS systems. Other lysis studies are in the preliminary stages.



  1. Williams, D.; Pramanik, S.; Haynes, C.; and Rosenzweig, Z. (2016, August). Synthesis and environmental studies of ZnSe/ZnS quantum dots. Poster presented at the 252nd American Chemical Society National Meeting & Exposition in the Colloids and Sci-Mix divisions.


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