Synthesis of Colloidal InP/ZnS Nanocrystals for a Photosensitizer
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Synthesis of Colloidal InP/ZnS Nanocrystals for a Photosensitizer
Seungyong Lee, Vanga R. Reddy, Jiang Wu, Rick Eyi and Omar Manasreh Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701, U.S.A.
ABSTRACT
Its intrinsic nontoxicity makes the direct band gap InP/ZnS core/shell be one of the most promising semiconductor nanocrystals for optoelectric applications, with the advantage of tuning the optical absorption range in the desired solar spectrum region. Highly luminescent and monodisperse InP/ZnS nanocrystals were synthesized in a non-coordinating solvent under a thorough degassing process. By varying synthesis scheme, different size InP/ZnS nanocrystals were grown. For the purpose of ensuring air stability, ZnS shell was grown. This ZnS shell improves the chemical stability in terms of oxidation prevention. Measurements of absorption and emission were performed on different InP/ZnS nanocrystals with different sizes. As expected, the measurements show a red-shift as the size of the InP/ZnS nanocrystals increased.
INTRODUCTION
Colloidal semiconductor nanocrystals (NCs) have drawn great interest in the past two decades due to their size dependent electrical and optical properties. Among them, a group of IIVI semiconducting NCs, especially CdSe quantum dots (QDs) show outstanding photostability, quantum yield (QY) and a tunable emission wavelength [1,2]. However, the intrinsic toxicity of CdSe QDs limits their applications. Among all II-VI and III-V semiconductors, InP QDs are expected to be the most promising ones, having a broad emission range similar to that of CdSe QDs without being toxic. However, the synthesis of high quality InP QDs with high emission efficiency, controlled size distribution, and good stability is challenging. In addition, the high flammability of the phosphorus precursor and the high activity of indium carboxylates’ hydrolysis are another struggle in synthesizing InP QDs. Our research focused on the synthesis of InP QDs covering the UV to the near infrared and the precise control of InP QDs size. In order to achieve this aim, three synthesis schemes were performed. Effects of parameters such as reaction temperature and reaction time on InP QDs were also explored and discussed. In addition, a simple way to deposit the InP/ZnS QDs on glass was examined. Above all things, this report intends to suggest a precise and plain way to synthesize desired InP QDs.
EXPERIMENT
The growth started by synthesizing indium(III) precursors. Indium acetate In(Ac)3 (10 mmol) was mixed with myristic acid (40 mmol) and heated to 140 ℃ under a nitrogen
atmosphere. The mixture was heated for 6 hours and then isolated by adding acetone. The product was filtered and dried. Myristic acid was again added to the product to make sure complete conversion of acetate to myristate. The final product, indium myristate In(Mt)3 was washed with acetone to remove any remaining myristic acid, dried and used as an indium precursor. Three synthesis methods were performed in order to have InP/ZnS
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