Improved optical properties of CdS quantum dots by ligand exchange

Comparelli, Roberto; Zezza, Fulvio; Striccoli, Marinella; Curri, M. Lucia; Tommasi, R.; Agostiano, Angela

doi:10.1016/j.msec.2003.09.121

Cited by 48 publications

(41 citation statements)

References 13 publications

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“…The enhancing effect of amine and phosphine oxide has been observed by others [10,18,19] and has been attributed to higher surface passivation due to greater coverage of coordinatively unsaturated Cd at the surface by the excess ligand. It is thought that this effect is particularly strong for the amine because it is a better ligand for the surface cadmium.…”

Section: Initial Effect Of Additivementioning

confidence: 59%

Stability and quantum yield effects of small molecule additives on solutions of semiconductor nanoparticles

Gaunt

Knight

Windsor

et al. 2005

Journal of Colloid and Interface Science

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Section: Initial Effect Of Additivementioning

confidence: 59%

Stability and quantum yield effects of small molecule additives on solutions of semiconductor nanoparticles

Gaunt

Knight

Windsor

et al. 2005

Journal of Colloid and Interface Science

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“…For example, the improvement of photoluminescence efficiency, [3][4][5] chemical reactivity, [6] the formation of two-dimensional and three-dimensional aggregates, [7,8] and the attachment of quantum dots to surfaces [6,[9][10][11] all involve the appropriate engineering of the ligands.…”

mentioning

confidence: 99%

Ligand Adsorption/Desorption on Sterically Stabilized InP Colloidal Nanocrystals: Observation and Thermodynamic Analysis

2006

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Colloidal semiconductor nanocrystals are widely studied in nanoscience and nanotechnology, since they implement almost perfectly the concept of a quantum dot. Even at room temperature, they have truly discrete energy levels, providing them with unique electrical and optical properties.[1] Typically, colloidal quantum dots come with an organic layer of ligands. These ligands play a key role during nanocrystal synthesis, as they form an adsorbed monolayer (capping) that slows down nanocrystal growth and stabilizes the nanocrystals in suspension.[2] In addition, the capping determines the properties and the processing possibilities of colloidal nanocrystals. For example, the improvement of photoluminescence efficiency, [3][4][5] chemical reactivity, [6] the formation of two-dimensional and three-dimensional aggregates, [7,8] and the attachment of quantum dots to surfaces [6,[9][10][11] all involve the appropriate engineering of the ligands.A number of literature reports demonstrate that solution 1 H NMR spectroscopy is a suitable technique for studying the capping of colloidal metal and semiconductor nanocrystals in situ, providing chemical and structural information on the ligands and on ligand exchange. [12][13][14][15][16][17] Herein, we present the results of a quantitative one-dimensional 1 H NMR study on suspensions of InP nanocrystals with trioctylphosphine oxide (TOPO) ligands. It is shown that the ligands are involved in an adsorption/desorption equilibrium, and that the adsorption isotherm can be obtained from the NMR data. In the case of TOPO adsorption at InP nanocrystals, the adsorption isotherm fits a Fowler isotherm, an extension of the Langmuir isotherm incorporating adsorbate-adsorbate interactions. [18,19] This fitting leads to a set of parameters characterizing the adsorption equilibrium, most notably, the equilibrium constant, the adsorbate density at full coverage, and the free energy of the adsorbate-adsorbate interaction. This work indicates that solution NMR spectroscopy not only provides an identification of the ligands, but may also be used to obtain quantitative, thermodynamic data on ligand adsorption. Figure 1 shows the aliphatic part of the 1 H NMR spectrum of a suspension of trioctylphosphine (TOP)-TOPO capped InP nanocrystals in [D 8 ] toluene (see Methods). As TOP and TOPO cannot be distinguished by 1 H NMR spectroscopy, we will only mention TOPO when discussing the capping molecules. The distinct resonances were attributed previously to free (N) and adsorbed TOPO (*).[17] For free TOPO, the end methyl group is found at 0.92 ppm; for adsorbed TOPO, it yields a broad resonance centered at 1.05 ppm. Both resonances are well resolved, and are integrated reliably by decomposing the spectrum into separate contributions (see Figure 1, inset). In this way, the concentrations of free and adsorbed TOPO can be determined quantitatively (see Methods). Figure 2 shows the con-

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“…These results indicate that the attachment of these molecules on the CdS surface does not modify the electronic states, i.e. no charge transfer reaction is involved in the presence of the amine molecules, although these molecules are known to act as electron donors for CdS particles [31][32][33].…”

Section: Resultsmentioning

confidence: 89%

Polyacrylic acid coating of highly luminescent CdS nanocrystals for biological labeling applications

Sato

Tachibana

Hattori

et al. 2008

Journal of Colloid and Interface Science

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Improved optical properties of CdS quantum dots by ligand exchange

Cited by 48 publications

References 13 publications

Stability and quantum yield effects of small molecule additives on solutions of semiconductor nanoparticles

Stability and quantum yield effects of small molecule additives on solutions of semiconductor nanoparticles

Ligand Adsorption/Desorption on Sterically Stabilized InP Colloidal Nanocrystals: Observation and Thermodynamic Analysis

Polyacrylic acid coating of highly luminescent CdS nanocrystals for biological labeling applications

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