Effect of Doping on the Structural and Optical Properties of Microwave-Assisted Synthesis of ZnSe@ZnS Core-Shell Quantum
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1207-N10-61
Effect of Doping on the Structural and Optical Properties of Microwave-Assisted Synthesis of ZnSe@ZnS Core-Shell Quantum Dots Sonia J. Bailon-Ruiz1, Oscar Perales-Perez1,2 Surinder P. Singh2 and Paul M. Voyles3 1
Department of Chemistry, University of Puerto Rico, Mayaguez, PR, USA. Department of Engineering Science & Materials, University of Puerto Rico, Mayaguez, PR, USA. 3 Materials Science and Engineering, University of Wisconsin at Madison, WI 53706-1595, USA ABSTRACT 2
Pure and Cu-doped quantum dots of ZnSe@ZnS were synthesized in aqueous phase using microwave irradiation at 140 °C. X-ray diffraction analyses suggested the development of a ZnSe-ZnS structure. UV-vis measurements evidenced that the presence of Cu species in quantum dots caused the blue shift of exciton peaks with respect to pure, i.e. non doped ones. Photoluminescence spectra of quantum dots synthesized at Zn/Cu mole ratios of 1/0.001 and 1/0.005 exhibited a very strong emission peak centered on ~ 515 nm. On the contrary, a weak emission peak was observed at 412 nm in pure ZnSe@ZnS quantum dots. The observed emission at 515 nm was attributed to the internal doping of Cu species, which should have induced d-d transitions in the host lattice. Quenching of the luminescence at 515 nm was observed for nominal Cu concentrations above 0.005 mM. INTRODUCTION Semiconductors Quantum Dots (QD’s) have attracted much attention because of their promising use in cell imaging and cancer therapy, among other bio-medical applications. The optical properties of these nanostructures can be tuned just by controlling their crystal-size, composition and shape at the nanoscale [1]. On the other hand, the incorporation of Cu species into II-VI semiconductors structures is expected to allow tunability of the resulting luminescence properties as well as enhancing the corresponding quantum yield. This tunable-photoluminescence kind of nanomaterials can be considered very promising candidates for photodynamic therapy (PDT) applications and biomarkers because their high efficiency as donors of energy [2-3]. PDT involves the use of a photosensitizing agent that goes through photochemical reaction and generates cytotoxic species such as singlet oxygen which destroy cancer cells. QD’s, via FRET mechanism (Förster Resonance Energy Transfer), could activate efficiently photosensitizing compounds. Regarding the type of candidate materials novel Zn-based QD’s are becoming potential replacements of Cd-based chalcogenides, which are expected to exhibit toxic effects in envisioned biomedical applications [4]. Although most of the research efforts were firstly focused on the study of single phase quantum dots, the possibility of tailoring optical properties through band gap engineering and doping of color centers in core-shell arrangements justifies the need to develop novel synthesis methods. Besides, the shell will also act as a passivation layer that prevents the core from oxidation. Furthermore, multicolor emissions could be achieved just by suitable doping of host
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