Sub-nanosecond charge dynamics in monodisperse Au nanoparticles (NPs) supported on TiO2 colloidal... more Sub-nanosecond charge dynamics in monodisperse Au nanoparticles (NPs) supported on TiO2 colloidal spheres are studied as a function of NP diameter using ultrafast transient absorption spectroscopy. The decay of the transmittance changes observed in the region of the plasmon resonance of the Au NPs following photoexcitation of the TiO2 spheres are well-described by a bi-exponential function consisting of a fast component of 2 ps duration associated with electron-phonon scattering, followed by a slow and relatively weak component associated with phonon-phonon scattering. The decay constant characterising the latter component was found to be dependent on the size of the Au NPs, rising from 49 ± 3 to 128 ± 6 ps as the diameter of the Au NPs increased from 12.2 ± 2.2 nm to 24.5 ± 2.8 nm, respectively.
Small (Weinheim an der Bergstrasse, Germany), Jan 27, 2014
Colloidal quantum dots (CQDs) are promising materials for novel light sources and solar energy co... more Colloidal quantum dots (CQDs) are promising materials for novel light sources and solar energy conversion. However, trap states associated with the CQD surface can produce non-radiative charge recombination that significantly reduces device performance. Here a facile post-synthetic treatment of CdTe CQDs is demonstrated that uses chloride ions to achieve near-complete suppression of surface trapping, resulting in an increase of photoluminescence (PL) quantum yield (QY) from ca. 5% to up to 97.2 ± 2.5%. The effect of the treatment is characterised by absorption and PL spectroscopy, PL decay, scanning transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. This process also dramatically improves the air-stability of the CQDs: before treatment the PL is largely quenched after 1 hour of air-exposure, whilst the treated samples showed a PL QY of nearly 50% after more than 12 hours.
Chemphyschem : a European journal of chemical physics and physical chemistry, Jan 14, 2015
Colloidal quantum dots (CQDs) can be used in conjunction with organic charge-transporting layers ... more Colloidal quantum dots (CQDs) can be used in conjunction with organic charge-transporting layers to produce light-emitting diodes, solar cells and other devices. The efficacy of CQDs in these applications is reduced by the non-radiative recombination associated with surface traps. Here we investigate the effect on the recombination dynamics in CdTe CQDs of the passivation of these surface traps by chloride ions. Radiative recombination dominates in these passivated CQDs, with the radiative lifetime scaling linearly with CQD volume over τr =20-55 ns. Before chloride passivation or after exposure to air, two non-radiative components are also observed in the recombination transients, with sample-dependent lifetimes typically of less than 1 ns and a few ns. The non-radiative dynamics can be explained by Auger-mediated trapping of holes and the lifetimes of this process calculated by an atomistic model are in agreement with experimental values if assuming surface oxidation of the CQDs.
1997 1st International Conference, Control of Oscillations and Chaos Proceedings (Cat. No.97TH8329), 1997
When the motion of a dynamical system is limited by a stop, the behaviour will be strongly nonlin... more When the motion of a dynamical system is limited by a stop, the behaviour will be strongly nonlinear due to the impacts that occur. Systems of this type are generally called impact oscillators and a plethora of dynamical states and bifurcations have been found, including subharmonics, period doublings and chaos. The paper studies the effect of nonidealities of impact oscillators.
ABSTRACT We present a method for calculating exciton and bi-exciton energies in type-II colloidal... more ABSTRACT We present a method for calculating exciton and bi-exciton energies in type-II colloidal quantum dots. Our methodology is based on an 8-band k p Hamiltonian of the zinc- blend structure, which incorporates the effects of spin-orbit interaction, strain between the core and the shell and piezoelectric potentials. Exciton states are found using the configuration interaction (CI) method that explicitly includes the effects of Coulomb interaction, as well as exchange and correlation between many-electron configurations. We pay particular attention to accurate modelling of the electrostatic interaction between quasiparticles. The model includes surface polarization and self-polarization effects due to the large difference in dielectric constants at the boundary of the QD.
We report salient spectroscopic properties of Tm 3+ -Yb 3+ and Tm 3+ -Ho 3+ -Yb 3+ co-doped fibre... more We report salient spectroscopic properties of Tm 3+ -Yb 3+ and Tm 3+ -Ho 3+ -Yb 3+ co-doped fibres for laser operations in the 1.88-1.99 μm and 2.05-2.11 μm range, respectively. The important differences in the pumping schemes at 1.09 μm and 1.60 μm are also explained for CW operation.
Organic Photorefractive and Photosensitive Materials for Holographic Applications, 2002
Quantum dots have significant potential as photosensitizers with a range of possible surface stru... more Quantum dots have significant potential as photosensitizers with a range of possible surface structures and a variety of materials available. Quantum dots composed of a cadmium selenide (CdSe) core and a cadmium sulfide (CdS) shell have been combined with poly ( ...
ABSTRACT We present recent results on the material, spectroscopic and laser properties of a range... more ABSTRACT We present recent results on the material, spectroscopic and laser properties of a range of Tm3+, Tm3+-Ho3+ and Dy3+ doped tellurium oxide (TeO2) based glasses in the 2-4 μm wavelength region.
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011
ABSTRACT In this talk, the author will describe the recent work in developing RE-doped tellurite ... more ABSTRACT In this talk, the author will describe the recent work in developing RE-doped tellurite fibre lasers emitting in the 2 μm spectral region. Tellurite fibres were fabricated which were doped with Tm3+ and Ho3+ for emission at ~1.9 μm and -2.1 μm, respectively. Yb3+/Tm3+ and Tm3+/Ho3+ co-doping was used to improve the overlap of the absorption spectrum of the fibres with the emission from various pump sources. Similarly, a novel triple doping (Yb3+/Tm3+/Ho3+) scheme was used to improve the efficiency of a Ho3+ doped tellurite fibre laser emitting at 2.1 μm when pumped at 1.1 μm. The important energy transfer processes in this triply-doped system are shown in the energy level diagram as shown in the paper.
We demonstrate a new grating-tuned coupled cavity which enhances mode selection and reduces the l... more We demonstrate a new grating-tuned coupled cavity which enhances mode selection and reduces the lasing threshold. This cavity consists of a Littrow cavity and an additional mirror to feedback the light, which is normally lost through grating reflection, into the cavity. This cavity corresponds to a three-mirror cavity with a spectral gate. We compare the overall performance of this cavity
The photophysical and photochemical reactions, after light absorption by a photosynthetic pigment... more The photophysical and photochemical reactions, after light absorption by a photosynthetic pigmentprotein complex, are among the fastest events in biology, taking place on timescales ranging from tens of femtoseconds to a few nanoseconds. The advent of ultrafast laser systems that produce pulses with femtosecond duration opened up a new area of research and enabled investigation of these photophysical and photochemical reactions in real time. Here, we provide a basic description of the ultrafast transient absorption technique, the laser and wavelengthconversion equipment, the transient absorption setup, and the collection of transient absorption data. Recent applications of ultrafast transient absorption spectroscopy on systems with increasing degree of complexity, from biomimetic light-harvesting systems to natural light-harvesting antennas, are presented. In particular, we will discuss, in this educational review, how a molecular understanding of the light-harvesting and photoprotective functions of carotenoids in photosynthesis is accomplished through the application of ultrafast transient absorption spectroscopy.
To expand the field of research in biological systems development of extra-sensitive analytical m... more To expand the field of research in biological systems development of extra-sensitive analytical methods is highly desirable. In this review, the latest advances in technologies relying on the fluorescence resonance energy transfer between fluorescent proteins (FP's) ...
ABSTRACT HgTe nanocrystals presently receive growing interest because the negative band gap in bu... more ABSTRACT HgTe nanocrystals presently receive growing interest because the negative band gap in bulk HgTe enables tunability of the gap from the infrared to the near infrared in quantum dots thanks to the quantum confinement. Therefore we propose a tight-binding model of HgTe which gives an accurate band structure in a wide energy range of energy compared to recent ab initio calculations. The inverted band structure near the Fermi level and its temperature dependence are also very well described. Using this model, we study the effects of the quantum confinement on the electronic structure of HgTe quantum dots. We calculate the optical absorption spectra of quantum dots with various shapes and diameters up to 10 nm, including excitonic effects using a configuration interaction approach [1]. The optical spectra are consistent with recent experimental data. We also simulate the multiple exciton generation and we discuss the results of ultrafast transient absorption spectroscopy experiments performed on HgTe nanocrystals. [1] G. Allan and C. Delerue, Phys. Rev. B 86, 165437 (2012). [2] A. Al-Otaify, S.V. Kershaw, S. Gupta, A.L. Rogach, G. Allan, C. Delerue and D.J. Binks, Phys. Chem. Chem. Phys. 15, 16864 (2013).
Summary form only given. Using a novel cavity architecture, we report significantly enhanced powe... more Summary form only given. Using a novel cavity architecture, we report significantly enhanced power and reduced threshold in a stable, single-longitudinal-mode (SLM) pulsed Ti:sapphire laser. The resonator incorporates a conventional grazing incidence cavity with an additional optic (zero-order mirror), which forms a coupled cavity in the form of a Michelson complex reflector.
Sub-nanosecond charge dynamics in monodisperse Au nanoparticles (NPs) supported on TiO2 colloidal... more Sub-nanosecond charge dynamics in monodisperse Au nanoparticles (NPs) supported on TiO2 colloidal spheres are studied as a function of NP diameter using ultrafast transient absorption spectroscopy. The decay of the transmittance changes observed in the region of the plasmon resonance of the Au NPs following photoexcitation of the TiO2 spheres are well-described by a bi-exponential function consisting of a fast component of 2 ps duration associated with electron-phonon scattering, followed by a slow and relatively weak component associated with phonon-phonon scattering. The decay constant characterising the latter component was found to be dependent on the size of the Au NPs, rising from 49 ± 3 to 128 ± 6 ps as the diameter of the Au NPs increased from 12.2 ± 2.2 nm to 24.5 ± 2.8 nm, respectively.
Small (Weinheim an der Bergstrasse, Germany), Jan 27, 2014
Colloidal quantum dots (CQDs) are promising materials for novel light sources and solar energy co... more Colloidal quantum dots (CQDs) are promising materials for novel light sources and solar energy conversion. However, trap states associated with the CQD surface can produce non-radiative charge recombination that significantly reduces device performance. Here a facile post-synthetic treatment of CdTe CQDs is demonstrated that uses chloride ions to achieve near-complete suppression of surface trapping, resulting in an increase of photoluminescence (PL) quantum yield (QY) from ca. 5% to up to 97.2 ± 2.5%. The effect of the treatment is characterised by absorption and PL spectroscopy, PL decay, scanning transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. This process also dramatically improves the air-stability of the CQDs: before treatment the PL is largely quenched after 1 hour of air-exposure, whilst the treated samples showed a PL QY of nearly 50% after more than 12 hours.
Chemphyschem : a European journal of chemical physics and physical chemistry, Jan 14, 2015
Colloidal quantum dots (CQDs) can be used in conjunction with organic charge-transporting layers ... more Colloidal quantum dots (CQDs) can be used in conjunction with organic charge-transporting layers to produce light-emitting diodes, solar cells and other devices. The efficacy of CQDs in these applications is reduced by the non-radiative recombination associated with surface traps. Here we investigate the effect on the recombination dynamics in CdTe CQDs of the passivation of these surface traps by chloride ions. Radiative recombination dominates in these passivated CQDs, with the radiative lifetime scaling linearly with CQD volume over τr =20-55 ns. Before chloride passivation or after exposure to air, two non-radiative components are also observed in the recombination transients, with sample-dependent lifetimes typically of less than 1 ns and a few ns. The non-radiative dynamics can be explained by Auger-mediated trapping of holes and the lifetimes of this process calculated by an atomistic model are in agreement with experimental values if assuming surface oxidation of the CQDs.
1997 1st International Conference, Control of Oscillations and Chaos Proceedings (Cat. No.97TH8329), 1997
When the motion of a dynamical system is limited by a stop, the behaviour will be strongly nonlin... more When the motion of a dynamical system is limited by a stop, the behaviour will be strongly nonlinear due to the impacts that occur. Systems of this type are generally called impact oscillators and a plethora of dynamical states and bifurcations have been found, including subharmonics, period doublings and chaos. The paper studies the effect of nonidealities of impact oscillators.
ABSTRACT We present a method for calculating exciton and bi-exciton energies in type-II colloidal... more ABSTRACT We present a method for calculating exciton and bi-exciton energies in type-II colloidal quantum dots. Our methodology is based on an 8-band k p Hamiltonian of the zinc- blend structure, which incorporates the effects of spin-orbit interaction, strain between the core and the shell and piezoelectric potentials. Exciton states are found using the configuration interaction (CI) method that explicitly includes the effects of Coulomb interaction, as well as exchange and correlation between many-electron configurations. We pay particular attention to accurate modelling of the electrostatic interaction between quasiparticles. The model includes surface polarization and self-polarization effects due to the large difference in dielectric constants at the boundary of the QD.
We report salient spectroscopic properties of Tm 3+ -Yb 3+ and Tm 3+ -Ho 3+ -Yb 3+ co-doped fibre... more We report salient spectroscopic properties of Tm 3+ -Yb 3+ and Tm 3+ -Ho 3+ -Yb 3+ co-doped fibres for laser operations in the 1.88-1.99 μm and 2.05-2.11 μm range, respectively. The important differences in the pumping schemes at 1.09 μm and 1.60 μm are also explained for CW operation.
Organic Photorefractive and Photosensitive Materials for Holographic Applications, 2002
Quantum dots have significant potential as photosensitizers with a range of possible surface stru... more Quantum dots have significant potential as photosensitizers with a range of possible surface structures and a variety of materials available. Quantum dots composed of a cadmium selenide (CdSe) core and a cadmium sulfide (CdS) shell have been combined with poly ( ...
ABSTRACT We present recent results on the material, spectroscopic and laser properties of a range... more ABSTRACT We present recent results on the material, spectroscopic and laser properties of a range of Tm3+, Tm3+-Ho3+ and Dy3+ doped tellurium oxide (TeO2) based glasses in the 2-4 μm wavelength region.
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference (CLEO EUROPE/EQEC), 2011
ABSTRACT In this talk, the author will describe the recent work in developing RE-doped tellurite ... more ABSTRACT In this talk, the author will describe the recent work in developing RE-doped tellurite fibre lasers emitting in the 2 μm spectral region. Tellurite fibres were fabricated which were doped with Tm3+ and Ho3+ for emission at ~1.9 μm and -2.1 μm, respectively. Yb3+/Tm3+ and Tm3+/Ho3+ co-doping was used to improve the overlap of the absorption spectrum of the fibres with the emission from various pump sources. Similarly, a novel triple doping (Yb3+/Tm3+/Ho3+) scheme was used to improve the efficiency of a Ho3+ doped tellurite fibre laser emitting at 2.1 μm when pumped at 1.1 μm. The important energy transfer processes in this triply-doped system are shown in the energy level diagram as shown in the paper.
We demonstrate a new grating-tuned coupled cavity which enhances mode selection and reduces the l... more We demonstrate a new grating-tuned coupled cavity which enhances mode selection and reduces the lasing threshold. This cavity consists of a Littrow cavity and an additional mirror to feedback the light, which is normally lost through grating reflection, into the cavity. This cavity corresponds to a three-mirror cavity with a spectral gate. We compare the overall performance of this cavity
The photophysical and photochemical reactions, after light absorption by a photosynthetic pigment... more The photophysical and photochemical reactions, after light absorption by a photosynthetic pigmentprotein complex, are among the fastest events in biology, taking place on timescales ranging from tens of femtoseconds to a few nanoseconds. The advent of ultrafast laser systems that produce pulses with femtosecond duration opened up a new area of research and enabled investigation of these photophysical and photochemical reactions in real time. Here, we provide a basic description of the ultrafast transient absorption technique, the laser and wavelengthconversion equipment, the transient absorption setup, and the collection of transient absorption data. Recent applications of ultrafast transient absorption spectroscopy on systems with increasing degree of complexity, from biomimetic light-harvesting systems to natural light-harvesting antennas, are presented. In particular, we will discuss, in this educational review, how a molecular understanding of the light-harvesting and photoprotective functions of carotenoids in photosynthesis is accomplished through the application of ultrafast transient absorption spectroscopy.
To expand the field of research in biological systems development of extra-sensitive analytical m... more To expand the field of research in biological systems development of extra-sensitive analytical methods is highly desirable. In this review, the latest advances in technologies relying on the fluorescence resonance energy transfer between fluorescent proteins (FP's) ...
ABSTRACT HgTe nanocrystals presently receive growing interest because the negative band gap in bu... more ABSTRACT HgTe nanocrystals presently receive growing interest because the negative band gap in bulk HgTe enables tunability of the gap from the infrared to the near infrared in quantum dots thanks to the quantum confinement. Therefore we propose a tight-binding model of HgTe which gives an accurate band structure in a wide energy range of energy compared to recent ab initio calculations. The inverted band structure near the Fermi level and its temperature dependence are also very well described. Using this model, we study the effects of the quantum confinement on the electronic structure of HgTe quantum dots. We calculate the optical absorption spectra of quantum dots with various shapes and diameters up to 10 nm, including excitonic effects using a configuration interaction approach [1]. The optical spectra are consistent with recent experimental data. We also simulate the multiple exciton generation and we discuss the results of ultrafast transient absorption spectroscopy experiments performed on HgTe nanocrystals. [1] G. Allan and C. Delerue, Phys. Rev. B 86, 165437 (2012). [2] A. Al-Otaify, S.V. Kershaw, S. Gupta, A.L. Rogach, G. Allan, C. Delerue and D.J. Binks, Phys. Chem. Chem. Phys. 15, 16864 (2013).
Summary form only given. Using a novel cavity architecture, we report significantly enhanced powe... more Summary form only given. Using a novel cavity architecture, we report significantly enhanced power and reduced threshold in a stable, single-longitudinal-mode (SLM) pulsed Ti:sapphire laser. The resonator incorporates a conventional grazing incidence cavity with an additional optic (zero-order mirror), which forms a coupled cavity in the form of a Michelson complex reflector.
Uploads
Papers by David Binks