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RISS 인기검색어
- 검색키워드
- 저자 : Gerd Bacher (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
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Magnetic Polaron Formation Dynamics in Mn^(2+)-Doped Colloidal Nanocrystals up to Room Temperature
Gerd Bacher,Lars Schneider,Rémi Beaulac,Paul I. Archer,Daniel R. Gamelin 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.51
The dynamics of exciton magnetic polaron (EMP) formation after pulsed laser excitation is studied in Mn^(2+)-doped colloidal CdSe nanocrystals. A transient energy shift of more than 130 meV at low temperature is obtained for the characteristic photoluminescence signal, and is related to the alignment of the Mn^(2+)-ion spins in the exchange field of the optically generated electron-hole pairs. The dynamics of laser induced magnetization are characterized by at least two time constants attributed to the EMP formation within a few hundreds of picoseconds, followed by a subsequent reorientation of the EMP spin complex in the nanosecond regime. We found a complete spin alignment up to temperatures of about 50 K and clear signatures of optically induced magnetization up to room temperature.
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Solution-Processed CuInS<sub>2</sub>-Based White QD-LEDs with Mixed Active Layer Architecture
Wepfer, Svenja,Frohleiks, Julia,Hong, A-Ra,Jang, Ho Seong,Bacher, Gerd,Nannen, Ekaterina American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.12
<P>Colloidal quantum dots (QDs) are attractive candidates for future lighting technology. However, in contrast to display applications, the realization of balanced white lighting devices remains conceptually challenging. Here, we demonstrate two-component white light-emitting QD-LEDs with high color rendering indices (CRI) up to 78. The implementation of orange CuInS2/ZnS (CIS/ZnS) QDs with a broad emission and high quantum yield together with blue ZnCdSe/ZnS QDs in a mixed approach allowed white light emission with low blue QD content. The devices reveal only a small color drift in a wide operation voltage range. The correlated color temperature (CCT) could be adjusted between 2200 and 7200 K (from warm white to cold white) by changing the volume ratio between orange and blue QDs (1:0.5 and 1:2).</P>
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Digital Doping in Magic-Sized CdSe Clusters
Muckel, Franziska,Yang, Jiwoong,Lorenz, Severin,Baek, Woonhyuk,Chang, Hogeun,Hyeon, Taeghwan,Bacher, Gerd,Fainblat, Rachel American Chemical Society 2016 ACS NANO Vol.10 No.7
<P>Magic-sized semiconductor clusters represent an exciting class of materials located at the boundary between quantum dots and molecules. It is expected that replacing single atoms of the host crystal with individual dopants in a one-by-one fashion can lead to unique modifications of the material properties. Here, we demonstrate the dependence of the magneto-optical response of (CdSe)(13) clusters on the discrete number of Mn2+. ion dopants. Using time-of-flight mass spectrometry, we are able to distinguish undoped, monodoped, and bidoped cluster species, allowing for an extraction of the relative amount of each species for a specific average doping concentration. A giant magneto-optical response is observed up to room temperature with clear evidence that exclusively monodoped clusters are magneto-optically active, whereas the Mn2+ ions in bidoped clusters couple antiferromagnetically and are magneto-optically passive. Mn2+-doped clusters therefore represent a system where magneto optical functionality is caused by solitary dopants, which might be beneficial for future solotronic applications.</P>
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Chemical Synthesis, Doping, and Transformation of Magic-Sized Semiconductor Alloy Nanoclusters
Yang, Jiwoong,Muckel, Franziska,Baek, Woonhyuk,Fainblat, Rachel,Chang, Hogeun,Bacher, Gerd,Hyeon, Taeghwan American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.19
<P>Nanoclusters are important prenucleation intermediates for colloidal nanocrystal synthesis. In addition, they exhibit many intriguing properties originating from their extremely small size lying between molecules and typical nanocrystals. However, synthetic control of multicomponent semiconductor nanoclusters remains a daunting goal. Here, we report on the synthesis, doping, and transformation of multielement magic-sized clusters, generating the smallest semiconductor alloys. We use Lewis acid base reactions at room temperature to synthesize alloy dusters containing three or four types of atoms. Mass spectrometry reveals that the alloy clusters exhibit 'magic-size' characteristics with chemical formula of ZnxCd13-xSe13 (x = 0-13) whose compositions are tunable between CdSe and ZnSe. Successful doping of these clusters creates a new class of diluted magnetic semiconductors in the extreme quantum confinement regime. Furthermore, the important role of these alloy clusters as prenucleation intermediates is demonstrated by low temperature transformation into quantum alloy nanoribbons and nanorods. Our study will facilitate the understanding of these novel diluted magnetic semiconductor nanoclusters, and offer new possibilities for the controlled synthesis of nanomaterials at the prenucleation stage, consequently producing novel multicomponent nanomaterials that are difficult to synthesize.</P>
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Yang, Jiwoong,Muckel, Franziska,Choi, Back Kyu,Lorenz, Severin,Kim, In Young,Ackermann, Julia,Chang, Hogeun,Czerney, Tamara,Kale, Vinayak S.,Hwang, Seong-Ju,Bacher, Gerd,Hyeon, Taeghwan American Chemical Society 2018 NANO LETTERS Vol.18 No.11
<P>Magic-sized clusters represent materials with unique properties at the border between molecules and solids and provide important insights into the nanocrystal formation process. However, synthesis, doping, and especially structural characterization become more and more challenging with decreasing cluster size. Herein, we report the successful introduction of Co<SUP>2+</SUP> ions into extremely small-sized CdSe clusters with the intention of using internal ligand field transitions to obtain structural insights. Despite the huge mismatch between the radii of Cd<SUP>2+</SUP> and Co<SUP>2+</SUP> ions (>21%), CdSe clusters can be effectively synthesized with a high Co<SUP>2+</SUP> doping concentration of ∼10%. Optical spectroscopy and mass spectrometry suggest that one or two Co<SUP>2+</SUP> ions are substitutionally embedded into (CdSe)<SUB>13</SUB> clusters, which is known as one of the smallest CdSe clusters. Using magnetic circular dichroism spectroscopy on the intrinsic ligand field transitions between the different <I>3d</I> orbitals of the transition metal dopants, we demonstrate that the Co<SUP>2+</SUP> dopants are embedded on pseudotetrahedral selenium coordinated sites despite the limited number of atoms in the clusters. A significant shortening of Co-Se bond lengths compared to bulk or nanocrystals is observed, which results in the metastability of Co<SUP>2+</SUP> doping. Our results not only extend the doping chemistry of magic-sized semiconductor nanoclusters, but also suggest an effective method to characterize the local structure of these extremely small-sized clusters.</P> [FIG OMISSION]</BR>
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