Synthesis and Characterization of Rare Earth (Tb 3+ and Yb 3+ ) Doped CdS/ZnS Core/Shell Nanocrystals for Enhanced Photo
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Synthesis and Characterization of Rare Earth (Tb3+ and Yb3+) Doped CdS/ZnS Core/Shell Nanocrystals for Enhanced Photovoltaic Efficiency Sandip Das1, and Krishna C. Mandal1 Department of Electrical Engineering, University of South Carolina, Columbia, SC 29208, USA
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ABSTRACT CdS host nanocrystals with 4.2-5.5 nm in diameter have been synthesized from air stable precursors via a synthetic chemical route and doped with rare earth (RE) terbium (Tb3+) and ytterbium (Yb3+) ions. RE3+-doped CdS cores were shelled by ZnS layers of different thicknesses. The resulting core/shell nanocrystals show a complete broadband absorption below 400-460 nm to the deep UV region depending on the size of the cores. RE3+-doped CdS nanocrystals showed a red shift in the emission as observed under irradiation of 302 nm UV light and was confirmed by room temperature photoluminescence (PL) measurements. The nanocrystals were further characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive x-ray (EDX) analysis. The results show that these RE3+-doped nanocrystals can be used as solar spectral matching downconversion material to enhance photovoltaic efficiency of existing solar cells. INTRODUCTION Doped bulk and 2-D semiconductor materials have lead to the design and fabrication of the modern electronic and optoelectronic devices. However, for nanoscale functional optoelectronic materials and devices, doping of semiconductor nanocrystals is an interesting field of research. Recently, doped semiconductor nanocrystals have been reported to have tunable optoelectronic and magnetic properties [1, 2]. However, only a few materials have been investigated as dopants and exploration of new doping agents for various host nanocrystals offers an interesting scope of research in this area of study. Therefore, it is important to explore and investigate the properties of various semiconductor nanocrystals (NCs) doped with different dopants to fabricate novel functional nanomaterials and devices for future optoelectronic applications. In this article we report rare earth (RE) doping of CdS nanocrystals by Tb3+ and Yb3+ and co-doped with these two RE ions. The RE3+-doped CdS nanocrystals were characterized by Ultraviolet-Visible (UV-Vis) absorbance and room temperature photoluminescence (PL) measurements. Our results show that Tb3+ and Yb3+-doped CdS nanocrytals show complete absorption below the band edge of the host CdS nanocrystals and a broadband emission in the visible region when excited below the band edge of the host CdS nanocrystals. This indicates that these RE-doped CdS nanocrystals can be used for optical downconversion, suitable for solar spectral matching to enhance solar cell efficiency. Doping of rare earth lanthanides to various host materials have been recently investigated for applications in Mid-IR Lasers [3, 4] and optical downconversion [5-9]. Although, many rare earth materials including Tb3+ and Yb3+ have been studied for downconversion applications [5-9], all of them were introduced either
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