Quantum confinement effects in chemically grown, stable ZnSe nanoclusters

Kumbhojkar, Neelesh; Mahamuni, Shailaja; Leppert, Valerie J.; Risbud, S. H.

doi:10.1016/s0965-9773(98)00055-5

Cited by 33 publications

(18 citation statements)

References 22 publications

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“…82 nm Stokes shift in the absorption-emission energy gap difference is described as a characteristic of quantum dot known to occur due to the presence of traps originating from surface levels and other intrinsic defects in literature. 26 In some cases, weak orange light emission at 600 nm has been observed by Se ion vacancy in the crystal lattice, but we did not observe such peak in our ZnSe-EDTA nanocrystal sample. In addition, in the ZnS:Mn nanocrystal, the orange light emission at 570 nm is attributed to the During the luminescence pathway, if surface defect states are located close to the conduction band, the direct energy transfer from the ZnS host to the Mn 2+ dopant ion is significantly interrupted, which can cause weakening the orange emission as well as enlarging Stokes shift.…”

Section: Methodscontrasting

confidence: 54%

EDTA Surface Capped Water-Dispersible ZnSe and ZnS:Mn Nanocrystals

Lee¹,

Lee²,

Huh³

et al. 2010

Bulletin of the Korean Chemical Society

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ZnSe and ZnS:Mn nanocrystals were synthesized via the thermal decomposition of their corresponding organometallic precursors in a hot coordinating solvent (TOP/TOPO) mixture. The organic surface capping agents were substituted with EDTA molecules to impart hydrophilic surface properties to the resulting nanocrystals. The optical properties of the water-dispersible nanocrystals were analyzed by UV-visible and room temperature solution photoluminescence (PL) spectroscopy. The powders were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), and confocal laser scanning microscopy (CLSM). The solution PL spectra revealed emission peaks at 390 (ZnSe-EDTA) and 597 (ZnS:Mn-EDTA) nm with PL efficiencies of 4.0 (former) and 2.4% (latter), respectively. Two-photon spectra were obtained by fixing the excitation light source wavelengths at 616 nm (ZnSe-EDTA) and 560 nm (ZnS:Mn-EDTA). The emission peaks appeared at the same positions to that of the PL spectra but with lower peak intensity. In addition, the morphology and sizes of the nanocrystals were estimated from the corresponding HR-TEM images. The measured average particle sizes were 5.4 nm (ZnSe-EDTA) with a standard deviation of 1.2 nm, and 4.7 nm (ZnS:Mn-EDTA) with a standard deviation of 0.8 nm, respectively.

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Section: Methodscontrasting

confidence: 54%

EDTA Surface Capped Water-Dispersible ZnSe and ZnS:Mn Nanocrystals

Lee¹,

Lee²,

Huh³

et al. 2010

Bulletin of the Korean Chemical Society

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“…This can be resulted from the fact that those PEO chains are too long for capping the ZnS:Mn nanocrystal surface so that the residual chains strongly interact with solvent water molecules, which can also quench the luminescence of the nanocrystal. 28 The stabilities of colloidal dispersions of the PEO capped nanocrystals were tested under various conditions. First, their dispersibility and photostability in aqueous solutions were tested by storing the colloids, prepared with ca.…”

Section: Resultsmentioning

confidence: 99%

Syntheses and Optical Characterizations of ZnS:Mn Nanocrystals Capped by Polyethylene Oxide Molecules of Varying Molecular Weights

Kim¹,

Hwang²

2010

Bulletin of the Korean Chemical Society

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Low-dimensional semiconducting nano-materials have gained significant attention over the past decade.1,2 These materials have found a wide range of applications in non-linear optics or electronic devices, and more recently as some bio-imaging or labeling agents due to their unique physical, chemical and optical properties. [3][4][5] Among the most important characteristics of these semiconducting nanocrystals is their optical properties which can vary greatly with the size of the nanocrystals, because the corresponding band gap energies differ even between materials of identical chemical composition. 6,7 ZnS:Mn nanocrystals (an orange light emitting nanophosphor) have attracted substantial interest on account of their high quantum yields and stability at ambient temperature, essential properties of commercial electro-luminescence devices.8 Considerable progress has been made in the synthetic techniques used to create such nanocrystals including gas, solid, and aqueous solution reactions via the thermal decomposition of organometallic precursors. However, these methods often require high temperatures and pressures and even the use of bio-hazardous substances. 9Water-dispersible semiconducting nanocrystals were developed especially for fluorescent labeling agents in living cells as an advanced bio-imaging technique. [10][11][12] They are expected to replace complicated or hazardous radioactive detection, and have formed the basis of very sensitive biological assays. In addition, semiconducting nanocrystals are much more efficient, sensitive and stable than the organic dyes currently used. Unfortunately, most highly luminescent semiconductor nanocrystals are grown in non-polar media, making them largely incompatible with any biological system. To date, there are several reports of solubilized hydrophobic nanocrystals in water, created by modifying the crystals' surfaces;13-15 however, generating water-dispersible and bio-compatible semiconductor nanocrystals which maintain high quantum efficiency and stability in a biological system still remains a great challenge. Several biocompatible amino acid molecule-capped ZnS:Mn nanocrystals have been synthesized in this laboratory. 16,17 In addition, more recently, we have synthesized mercaptoacetate (MAA) molecules capped water-dispersible ZnS:Mn nanocrystal. The surface capping MAA molecules were characterized by FT-Raman spectroscopy, and the specific coordination mode of the MAA molecule was determined by a DFT calculation. 18This paper describes the synthesis of water-dispersible ZnS: Mn nanocrystals whose surfaces are capped by polyethylene oxide molecules of varying molecular weight. Their physical and optical properties are also investigated. Historically, the abbreviations PEG (polyethylene glycol) and PEO (polyethylene oxide) refer to oligomers or polymers of ethylene oxide molecules. PEG has tended to refer to oligomers and polymers with a molecular mass below 20,000 g/mol, while PEO to polymers with a molecular mass above that. 19 This article refers to all pol...

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“…The large Stokes shift in the absorption-emission energy gap difference can be described as a characteristic of zero-dimensional nanocrystals, which is usually due to the presence of traps originating from surface levels and other intrinsic defects. 19 The surface defect on the ZnSe:Mn nanocrystal probably resulted from incomplete capping by the surfactant TOPO ligands, or from the zinc metal cation or selenide anion vacancy on the surface of the crystal lattice. In the ZnSe:Mn nanocrystal, the orange light emission at 572 nm is attributed to the 20 In the luminescence pathway, if the surface defect states are located close to the conduction band, direct energy transfer from the ZnSe host to the Mn 2+ dopant ion is significantly interrupted, which can cause weakening in the orange emission as well as enlarging the Stokes shift.…”

Section: Notesmentioning

confidence: 99%