title: Highly luminescent silica-coated CdS/CdSe/CdS nanoparticles with strong chemical robustness and excellent thermal stability.
abstract: We present facile synthesis of bright CdS/CdSe/CdS@SiO2nanoparticles with 72% of quantum yields (QYs) retaining ca 80% of the original QYs. The main innovative point is the utilization of the highly luminescent CdS/CdSe/CdS seed/spherical quantum well/shell (SQW) as silica coating seeds. The significance of inorganic semiconductor shell passivation and structure design of quantum dots (QDs) for obtaining bright QD@SiO2is demonstrated by applying silica encapsulation via reverse microemulsion method to three kinds of QDs with different structure: CdSe core and 2 nm CdS shell (CdSe/CdS-thin); CdSe core and 6 nm CdS shell (CdSe/CdS-thick); and CdS core, CdSe intermediate shell and 5 nm CdS outer shell (CdS/CdSe/CdS-SQW). Silica encapsulation inevitably results in lower photoluminescence quantum yield (PL QY) than pristine QDs due to formation of surface defects. However, the retaining ratio of pristine QY is different in the three silica coated samples; for example, CdSe/CdS-thin/SiO2shows the lowest retaining ratio (36%) while the retaining ratio of pristine PL QY in CdSe/CdS-thick/SiO2and SQW/SiO2is over 80% and SQW/SiO2shows the highest resulting PL QY. Thick outermost CdS shell isolates the excitons from the defects at surface, making PL QY relatively insensitive to silica encapsulation. The bright SiO2-coated SQW sample shows robustness against harsh conditions, such as acid etching and thermal annealing. The high luminescence and long-term stability highlights the potential of using the SQW/SiO2nanoparticles in bio-labeling or display applications.
authors.affiliation: Department of Chemical and Bimolecular Engineering (BK21+ Program), KAIST Institute for the Nanocentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea.
authors.forename: Nianfang
authors.initials: N
authors.lastname: Wang
authors.forename: Sungjun
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authors.lastname: Koh
authors.forename: Byeong Guk
authors.initials: BG
authors.lastname: Jeong
authors.forename: Dongkyu
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authors.lastname: Lee
authors.forename: Whi Dong
authors.initials: WD
authors.lastname: Kim
authors.forename: Kyoungwon
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authors.lastname: Park
authors.forename: Min Ki
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authors.lastname: Nam
authors.forename: Kangha
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authors.lastname: Lee
authors.forename: Yewon
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authors.lastname: Kim
authors.forename: Baek-Hee
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authors.lastname: Lee
authors.forename: Kangtaek
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authors.lastname: Lee
authors.forename: Wan Ki
authors.initials: WK
authors.lastname: Bae
authors.forename: Doh C
authors.initials: DC
authors.lastname: Lee