Full Color Emission from II-VI Semiconductor Quantum Dot-Polymer Composites

Lee, J.; Sundar, Vikram C.; Heine, Johanna; Bawendi, Moungi G.; Jensen, Klavs F.

doi:10.1002/1521-4095(200008)12:15<1102::aid-adma1102>3.0.co;2-j

Cited by 781 publications

(552 citation statements)

References 13 publications

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“…Proton T 2 relaxation times were measured from the delay time dependence of the intensity in the Carr-PurcellMeiboom-Gill (CPMG) echo experiment. 1 H NMR diffusion measurements were performed at 499.78 MHz using the stimulated echo (STE) pulsed field gradient (PFG) procedure, 27 with a square field gradient pulse of constant duration (δ) equal to 5 ms and a variable gradient pulse amplitude (g). The field gradient pulses were applied along the longitudinal (z) direction exclusively.…”

Section: Methodsmentioning

confidence: 99%

Pulsed Field Gradient NMR Studies of Polymer Adsorption on Colloidal CdSe Quantum Dots

et al. 2008

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Pulsed field gradient nuclear magnetic resonance (PFG NMR) experiments have been used to examine ligand exchange between poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMA) (M n ) 12 000, M w /M n ) 1.20, N n ) 78) and trioctylphosphine oxide (TOPO) bound to the surface of CdSe/TOPO quantum dots (QDs). We show that PFG 1 H NMR can quantify the displacement of TOPO by PDMA through its ability to differentiate signals due to TOPO bound to the QDs versus those from TOPO molecules free in solution. For CdSe QDs with a band edge absorption maximum at 558 nm (diameter 2.7 nm by transmission electron microscopy), we determined that, at saturation, 8 polymer chains on average displace greater than 90% of the surface TOPO groups. At partial saturation, with an average of 6 polymer chains/QD, each TOPO displaced requires 28 DMA repeat units. Assuming that one Me 2 N-group binds to a surface Cd 2+ for each TOPO displaced, we infer that only about 3% of the DMA units are directly bound to the surface. The remaining groups are present as loops or tails that protrude into the solvent and increase the hydrodynamic diameter of the particles.

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Section: Methodsmentioning

confidence: 99%

Pulsed Field Gradient NMR Studies of Polymer Adsorption on Colloidal CdSe Quantum Dots

et al. 2008

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“…1 High efficiencies are especially important for application of QDs as luminescent biolabels, 2 in QD lasers, 3 in spectral converters for warm white LEDs, 4,5 electroluminescent devices, 6 and solar concentrators. 7 Luminescence efficiencies are strongly temperature-dependent.…”

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confidence: 99%

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

et al. 2012

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A high luminescence efficiency is an important property of colloidal quantum dots (QDs), and quantum yields higher than 90% have been reported for coreÀshell QDs. 1 High efficiencies are especially important for application of QDs as luminescent biolabels, 2 in QD lasers, 3 in spectral converters for warm white LEDs, 4,5 electroluminescent devices, 6 and solar concentrators. 7 Luminescence efficiencies are strongly temperature-dependent. 8 Extensive temperature-dependent luminescence studies for colloidal QDs have been conducted at cryogenic temperatures (0.3À300 K). 9À15 In this temperature region, interesting effects were observed, including a prolonged lifetime below 20 K related to brightÀdark state splitting, 11,16 thermally activated quenching due to surface defect states, 9,10,17 and temperature antiquenching assigned to a phase transition in the capping layer. 14,15 However, the luminescence properties of QDs above room temperature (RT) are hardly investigated, and yet, for most applications in luminescent devices, the working temperature is higher than 300 K. An interesting example is the recent application of QDs as color converters in warm-white LEDs, 18 in which QDs serve as narrow band red emitters under excitation with blue light from a (In,Ga)N LED. The narrow emission bandwidth renders QDs superior to classical phosphors based on broad band emission from luminescent ions. 19 In high-power LEDs for general lighting applications, the heat generated in the pÀn junction and phosphor converter layer leads to temperatures as high as 150À200°C in the layer applied on top of the blue diode. 20 To avoid these high temperatures, the QD phosphor layer can be placed in a more remote configuration. Still, temperatures in such a configuration are expected to be well above 50°C due to heat dissipation of the QDs themselves (excess energy from converting the blue into red light). Clearly, the quenching of QD luminescence at elevated temperatures is relevant for application of QDs in luminescent devices, and a better insight in the quenching behavior is needed.Despite its importance, research on luminescence temperature quenching above RT is very limited for QDs. It is theoretically expected for a QD to have a very high luminescence quenching temperature (T q ). Three generally accepted mechanisms for thermal quenching involve thermally activated crossover from the excited state to the ground state, multiphonon relaxation, and thermally activated photoionization. The first mechanism is generally depicted in a simple configurational coordinate diagram. 8,21 The energy difference between the minimum * Address correspondence to a.meijerink@uu.nl.Received for review July 18, 2012 and accepted September 14, 2012. Published online 10.1021/nn303217qABSTRACT Thermal quenching of quantum dot (QD) luminescence is important for application in luminescent devices. Systematic studies of the quenching behavior above 300 K are, however, lacking. Here, high-temperature (300À500 K) luminescence studies are reported for highly ef...

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“…This versatility leads to numerous photonic applications, such as optical fiber amplifiers, 1,2 color displays using light-emitting diode arrays, 3 optical temperature probes, 4 and biomedical imaging. 5 Conjugation of QDs with antibodies yields biomarkers that compete with traditional organic fluorescent tags in terms of biocompatibility, excitation and filtering simplicity, and photostability.…”

mentioning

confidence: 99%

Synthesis kinetics of CdSe quantum dots in trioctylphosphine oxide and in stearic acid

Dickerson

Irving

Herz

et al. 2005

Applied Physics Letters

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A diffusion-barrier model described the early evolution of size-dependent photoluminescence emission from CdSe quantum dots formed by organometallic synthesis. Emission peak widths, emission redshift rates, and nanocrystal growth rates all decreased to a minimum at a reaction completion time. Growth after the completion time by Ostwald ripening was marked by a doubling of the activation energy. The temperature dependence of both reaction completion rates and photoluminescence redshift rates followed Arrhenius behavior governed by activation energies that increased with solvent molecular weight, in this limited case. In stearic acid and in trioctylphosphine oxide, the typical activation energies were 0.6±0.1 and 0.92±0.26eV∕molecule, respectively.

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Full Color Emission from II-VI Semiconductor Quantum Dot-Polymer Composites

Cited by 781 publications

References 13 publications

Pulsed Field Gradient NMR Studies of Polymer Adsorption on Colloidal CdSe Quantum Dots

Pulsed Field Gradient NMR Studies of Polymer Adsorption on Colloidal CdSe Quantum Dots

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

Synthesis kinetics of CdSe quantum dots in trioctylphosphine oxide and in stearic acid

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