Spectroscopy and Femtosecond Dynamics of Type-II CdSe/ZnTe Core−Shell Semiconductor Synthesized via the CdO Precursor

Chen, Chun‐Yen; Cheng, Chih-Jen; Yu, Jen Kan; Pu, Shih Chieh; Cheng, Yi Ming; Chou, Pi‐Tai; Chou, Yi Hsuan; Chiu, Hsin‐Tien

doi:10.1021/jp049177w

Cited by 86 publications

(72 citation statements)

References 26 publications

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“…The measurements of electrochemistry, absorption, emission and nanosecond time-resolved transient absorption were performed according to previously reported procedures (42) and described in detail in SI Materials and Methods. Steady-state NIR emission spectroscopy has been reported (43) and is described in detail in SI Materials and Methods. The details of femtosecond time-resolved transient absorption and up-conversion experiments are described in SI Materials and Methods.…”

Section: Methodsmentioning

confidence: 99%

The remarkable influence of M ₂ δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

Burdziński

Chisholm

Chou

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Oligothiophenes incorporating MM quadruple bonds have been prepared from the reactions between Mo2(TiPB)4 (TiPB ‫؍‬ 2,4,6-triisopropyl benzoate) and 3,4-dihexyl-2,2-:5,2؆-terthiophene-5,5؆-dicarboxylic acid. The oligomers of empirical formula Mo2(TiPB)2(O2C(Th)-C4(n-hexyl)2S-(Th)CO2) are soluble in THF and form thin films with spin-coating (Th ‫؍‬ thiophene). The reactions between Mo2(TiPB)4 and 2-thienylcarboxylic acid (Th-H), 2,2-bithiophene-5-carboxylic acid (BTh-H), and (2,2:5,2؆-terthiophene)-5-carboxylic acid (TTh-H) yield compounds of formula trans-Mo2(TiPB)2L2, where L ‫؍‬ Th, BTh, and TTh (the corresponding thienylcarboxylate), and these compounds are considered as models for the aforementioned oligomers. In all cases, the thienyl groups are substituted or coupled at the 2,5 positions. Based on the x-ray analysis, the molecular structure of trans-Mo2(TiPB)2(BTh)2 reveals an extended L-M2␦-L conjugation. Calculations of the electronic structures on model compounds, in which the TiPB are substituted by formate ligands, reveal that the HOMO is mainly attributed to the M2␦ orbital, which is stabilized by back-bonding to one of the thienylcarboxylate * combinations, and the LUMO is an in-phase combination of the thienylcarboxylate * orbitals. The compounds and the oligomers are intensely colored due to M2␦-thienyl carboxylate * charge transfer transitions that fall in the visible region of the spectrum. For the molybdenum complexes and their oligomers, the photophysical properties have been studied by steady-state absorption spectroscopy and emission spectroscopy, together with time-resolved emission and transient absorption for the determination of relaxation dynamics. Remarkably, THF solutions the molybdenum complexes show room-temperature dual emission, fluorescence and phosphorescence, originating mainly from 1 MLCT and 3 MM(␦␦*) states, respectively. With increasing number of thienyl rings from 1 to 3, the observed lifetimes of the 1 MLCT state increase from 4 to 12 ps, while the phosphorescence lifetimes are Ϸ80 s. The oligomers show similar photophysical properties as the corresponding monomers in THF but have notably longer-lived triplet states, Ϸ200 s in thin films. These results, when compared with metallated oligothiophenes of the later transition elements, reveal that M 2␦-thienyl conjugation leads to a very small energy gap between the 1 MLCT and 3 MLCT states of <0.6 eV.photophysics ͉ dual emission B ecause of their potential applications in optoelectronic and magnetic devices, conjugated organic polymers have received much attention (1-3), and oligothiophenes, which constitute one important subclass of these materials, have been found to show excellent hole transport properties (3-7). We have been interested for some time in incorporating MM quadruple bonds into these oligomers by use of the carboxylate tether (8-10), such that the M 2 ␦ electrons can be brought into conjugation with an extended -framework of the thiophene moiety. As shown in Scheme 1, the out-of-phase combination of the carbo...

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Section: Methodsmentioning

confidence: 99%

The remarkable influence of M ₂ δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

Burdziński

Chisholm

Chou

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…[12][13][14][15][16][17][18][19][20][21][22] Previous studies have suggested that CdSe nanocrystals undergo two main modes of exciton relaxation when excited at or near the band edge. 23 The first and most desirable mode for fluorescent applications is simple band edge recombination, resulting in the fundamental band edge emission feature in the static fluorescence spectrum.…”

Section: Effects Of Surface Passivation On the Exciton Dynamics Of CDmentioning

confidence: 99%

Effects of surface passivation on the exciton dynamics of CdSe nanocrystals as observed by ultrafast fluorescence upconversion spectroscopy

Kippeny

Bowers

Dukes

et al. 2008

The Journal of Chemical Physics

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The exciton dynamics of CdSe nanocrystals are intimately linked to the surface morphology. Photo-oxidation of the selenium surfaces of the nanocrystal leads to an increase in radiative decay efficiency from both the band edge and deep trap emission states. The addition of the primary amine hexadecylamine curtails nonradiative excitonic decay attributed to the dangling surface selenium orbitals by passivation of those trap sites by the methylene protons on the amine, leading to enhanced band edge emission and the absence of deep trap emission. Furthermore, CdSeZnSe core/shell nanocrystals are not immune from contributions from surface states because of the alignment of the band structures of the core and shell materials.

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“…Hence, the electron wave function is restricted to the shell, and the quality of the nanocrystals' surface plays a more essential role in fluorescence QY. Because they were more susceptible to compression, CdTe nanocrystals of 2.17 nm probably contained more surface defects, which determined an abrupt decrease in QY when more than one CdS monolayer was deposited on the core [35]. All of the plots revealed that the FWHM values increased as more CdS layers grew on the nanocrystals' surface.…”

Section: Cdte/cds Qds Synthesized Via the Silar Methodsmentioning

confidence: 99%

Water-Soluble CdTe/CdS Core/Shell Semiconductor Nanocrystals: How Their Optical Properties Depend on the Synthesis Methods

et al. 2016

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Abstract:We conducted a comparative synthesis of water-soluble CdTe/CdS colloidal nanocrystalline semiconductors of the core/shell type. We prepared the CdS shell using two different methods: a one-pot approach and successive ionic layer adsorption and reaction (SILAR); in both cases, we used 3-mercaptopropionic acid (MPA) as the surface ligand. In the one-pot approach, thiourea was added over the freshly formed CdTe dispersion, and served as the sulfur source. We achieved thicker CdS layers by altering the Cd:S stoichiometric ratio (1:1, 1:2, 1:4, and 1:8). The Cd:S ratios 1:1 and 1:2 furnished the best optical properties; these ratios also made the formation of surface defects less likely. For CdTe/CdS obtained using SILAR, we coated the surface of three differently sized CdTe cores (2.17, 3.10, and 3.45 nm) with one to five CdS layers using successive injections of the Cd 2+ and S 2-ions. The results showed that the core size influenced the optical properties of the materials. The deposition of three to five layers over the surface of smaller CdTe colloidal nanocrystals generated strain effects on the core/shell structure.

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Spectroscopy and Femtosecond Dynamics of Type-II CdSe/ZnTe Core−Shell Semiconductor Synthesized via the CdO Precursor

Cited by 86 publications

References 26 publications

The remarkable influence of M ₂ δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

The remarkable influence of M ₂ δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

Effects of surface passivation on the exciton dynamics of CdSe nanocrystals as observed by ultrafast fluorescence upconversion spectroscopy

Water-Soluble CdTe/CdS Core/Shell Semiconductor Nanocrystals: How Their Optical Properties Depend on the Synthesis Methods

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Spectroscopy and Femtosecond Dynamics of Type-II CdSe/ZnTe Core−Shell Semiconductor Synthesized via the CdO Precursor

Cited by 86 publications

References 26 publications

The remarkable influence of M 2 δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

The remarkable influence of M 2 δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

Effects of surface passivation on the exciton dynamics of CdSe nanocrystals as observed by ultrafast fluorescence upconversion spectroscopy

Water-Soluble CdTe/CdS Core/Shell Semiconductor Nanocrystals: How Their Optical Properties Depend on the Synthesis Methods

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The remarkable influence of M ₂ δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds

The remarkable influence of M ₂ δ to thienyl π conjugation in oligothiophenes incorporating MM quadruple bonds