ORCID Profile
0000-0001-7821-7208
Current Organisation
University of St Andrews
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Publisher: Wiley
Date: 06-10-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B717750J
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C1NJ20493A
Publisher: IEEE
Date: 2005
Publisher: American Chemical Society (ACS)
Date: 08-06-2011
DOI: 10.1021/JP200668X
Abstract: We have carried out absorption, time-resolved fluorescence, and fluorescence quantum yield measurements of four new soluble anthracene derivatives. They show natural radiative lifetimes in the range of 2.5-4.4 ns, which is 5-10 times shorter than those reported for unsubstituted anthracene. The 9,10-bis(phenylethynyl)anthracene (BPEA) derivatives show the largest fluorescence transition dipoles, which is attributed to extended π-conjugation between anthracene and phenyls through acetylene linkages. Spin-cast films of the BPEA derivatives show strong fluorescence quenching by weakly emitting low energy excitations, which is attributed to excimer-like traps. Quenching is significantly reduced when bulky dendrons are attached so that they give maximum coverage of the emitting chromophore and prevent their aggregation. The results show that anthracene derivatives can be developed into efficient solution-processable fluorescent emitters for the blue and green spectral regions.
Publisher: AIP Publishing
Date: 21-06-2010
DOI: 10.1063/1.3456374
Abstract: Color information is much less useful to machine vision systems than to people because the spectrum of light illuminating a scene is unknown. For scenes illuminated by daylight, color information can be made significantly more useful to machine vision systems if the scene is imaged using sensors with a specifically chosen combination of spectral responses. In this paper we show that detectors with a full width at half maximum of up to 100 nm can give good color discrimination, and that conjugated dendrimer chromophores have the spectral properties required to allow machine vision systems to confidently use color information.
Publisher: SPIE
Date: 18-08-2005
DOI: 10.1117/12.616863
Publisher: Wiley
Date: 15-10-2018
Abstract: High-efficiency pure blue phosphorescent organic light-emitting diodes (OLEDs) remain one of the grand challenges, principally because the emissive complexes employed either do not possess sufficiently high photoluminescence quantum yields or exhibit unsatisfactory Commission International de l'Éclairage (CIE) coordinates. Here two deep-blue-emitting homoleptic iridium(III) complexes are reported and OLEDs are demonstrated with CIE coordinates of (0.15, 0.05) and maximum external quantum efficiency of 13.4%, which decreases slightly to 12.5% at 100 cd m
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B400160E
Publisher: SPIE-Intl Soc Optical Eng
Date: 12-10-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B820235D
Publisher: Wiley
Date: 21-12-2009
Abstract: Phosphorescent light-emitting transistors, in which light emission from singlet and triplet energy levels is harvested using solution-processed materials, are presented. While a green phosphorescent dendrimer exhibits an external quantum efficiency of 0.45% at 480 cd m(-2) , a red polymer hosphorescent small-molecule blend produces a brightness exceeding 30 cd m(-2) with a relatively high hole mobility of 2.5 × 10(-2) cm(2) V(-1) s(-1) .
Publisher: Optica Publishing Group
Date: 2007
DOI: 10.1364/OE.15.003962
Abstract: We report the demonstration of compact fluidic fibre lasers based on capillary tubes and photonic crystal fibres, featuring single channel and multiple laterally integrated fluidic lasers respectively. Their preparation was based on capillary action and lasing occurred without the need for external mirrors or lithographically defined microstructures. The fibre lasers were found to be tunable by varying the chromophore density in the liquid core and a functional wavelength selectivity mechanism inherent in both types of lasers provided a long free spectral range that does not correspond to the length of the fibres. The enhanced mode spacing is attributed to a Vernier resonant effect.
Publisher: The Optical Society
Date: 23-01-2012
DOI: 10.1364/OE.20.00A213
Publisher: American Chemical Society (ACS)
Date: 08-12-2011
DOI: 10.1021/JP2043703
Publisher: AIP Publishing
Date: 22-06-2009
DOI: 10.1063/1.3149827
Abstract: A tunable two-photon pumped solid-state laser based on polyfluorene is reported. A detailed investigation of the two-photon absorption in polyfluorene for both nanosecond and femtosecond time regimes in solution, and solid-state allows the determination of the most favorable conditions for lasing. Tunable distributed feedback lasers are made by spin coating from a polyfluorene solution on corrugated silica substrates and lasing is achieved under two-photon excitation at 640 nm with an absorbed energy density at lasing threshold of 1.3 mJ/cm2. These results highlight an alternative pumping scheme for blue organic semiconductor lasers.
Publisher: AIP Publishing
Date: 25-11-2002
DOI: 10.1063/1.1524029
Publisher: AIP Publishing
Date: 29-12-2003
DOI: 10.1063/1.1633336
Abstract: Electrophosphorescent dendrimers are promising materials for highly efficient light-emitting diodes. They consist of a phosphorescent core onto which dendritic groups are attached. Here, we present an investigation into the optical and electronic properties of highly efficient phosphorescent dendrimers. The effect of dendrimer structure on charge transport and optical properties is studied using temperature-dependent charge-generation-layer time-of-flight measurements and current voltage (I–V) analysis. A model is used to explain trends seen in the I–V characteristics. We demonstrate that fine tuning the mobility by chemical structure is possible in these dendrimers and show that this can lead to highly efficient bilayer dendrimer light-emitting diodes with neat emissive layers. Power efficiencies of 20 lm/W were measured for devices containing a second-generation (G2) Ir(ppy)3 dendrimer with a 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene electron transport layer.
Publisher: IEEE
Date: 06-2007
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B902374G
Publisher: AIP Publishing
Date: 15-06-2009
DOI: 10.1063/1.3152782
Abstract: A blue-emitting distributed feedback laser based on a star-shaped oligofluorene truxene molecule is presented. The gain, loss, refractive index, and (lack of) anisotropy are measured by lified spontaneous emission and variable-angle ellipsometry. The waveguide losses are very low for an organic semiconductor gain medium, particularly for a neat film. The results suggest that truxenes are promising for reducing loss, a key parameter in the operation of organic semiconductor lasers. Distributed feedback lasers fabricated from solution by spin-coating show a low lasing threshold of 270 W/cm2 and broad tunability across 25 nm in the blue part of the spectrum.
Publisher: Wiley
Date: 2005
DOI: 10.1889/1.2036382
Publisher: SPIE
Date: 16-02-2004
DOI: 10.1117/12.512062
Publisher: Royal Society of Chemistry (RSC)
Date: 2000
DOI: 10.1039/A904274A
Publisher: American Chemical Society (ACS)
Date: 10-07-2009
DOI: 10.1021/JA903157E
Abstract: Solution-processable blue phosphorescent emitters with high luminescence efficiency are highly desirable for large-area displays and lighting applications. This report shows that when a fac-tris[1-methyl-5-(4-fluorophenyl)-3-n-propyl-1H-[1,2,4]triazolyl]iridium(III) complex core is encapsulated by rigid high-triplet-energy dendrons, both the physical and photophysical properties can be optimized. The high-triplet-energy and rigid dendrons were composed of twisted biphenyl dendrons with the twisting arising from the use of tetrasubstituted branching phenyl rings. The blue phosphorescent dendrimer was synthesized using a convergent approach and was found to be solution-processable and to possess a high glass transition temperature of 148 degrees C. The dendrimer had an exceptionally high solution photoluminescence quantum yield (PLQY) of 94%, which was more than three times that of the simple parent core complex (27%). The rigid and high-triplet-energy dendrons were also found to control the intermolecular interactions that lead to the quenching of the luminescence in the solid state, and the film PLQY was found to be 60% with the emission having Commission Internationale de l'Eclairage coordinates of (0.16, 0.16). The results demonstrate that dendronization of simple chromophores can enhance their properties. Single layer neat dendrimer organic light-emitting diodes (OLEDs) had an external quantum efficiency (EQE) of 0.4% at 100 cd/m(2). Bilayer devices with an electron transport layer gave improved EQEs of up to 3.9%. Time-resolved luminescence measurements suggest that quenching of triplets by the electron transport layer used in the bilayer OLEDs limits performance.
Publisher: American Chemical Society (ACS)
Date: 06-08-2010
DOI: 10.1021/MA101363H
Publisher: SPIE
Date: 16-09-2002
DOI: 10.1117/12.483063
Publisher: SPIE
Date: 13-09-2012
DOI: 10.1117/12.928494
Publisher: IEEE
Date: 05-2007
Publisher: Elsevier BV
Date: 09-2003
Publisher: Wiley
Date: 19-10-2011
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2010
Publisher: Elsevier BV
Date: 07-2010
Publisher: Wiley
Date: 19-05-2008
Publisher: AIP Publishing
Date: 07-2020
DOI: 10.1063/5.0011229
Abstract: Lead halide perovskites are very promising materials for many optoelectronic devices. They are low cost, photostable, and strongly photoluminescent materials, but so far have been little studied for sensing. In this article, we explore hybrid perovskites as sensors for explosive vapor. We tune the dimensionality of perovskite films in order to modify their exciton binding energy and film morphology and explore the effect on sensing response. We find that tuning from the 3D to the 0D regime increases the PL quenching response of perovskite films to the vapor of dinitrotoluene (DNT)—a molecule commonly found in landmines. We find that films of 0D perovskite nanocrystals work as sensitive and stable sensors, with strong PL responses to DNT molecules at concentrations in the parts per billion range. The PL quenching response can easily be reversed, making the sensors reusable. We compare the response to several explosive vapors and find that the response is strongest for DNT. These results show that hybrid perovskites have great potential for vapor sensing applications.
Publisher: American Chemical Society (ACS)
Date: 22-03-2012
DOI: 10.1021/MA300306D
Publisher: Optica Publishing Group
Date: 2006
DOI: 10.1364/OE.14.009211
Abstract: We report the demonstration of a compact, all-solid-state polymer laser system comprising of a Gallium Nitride (GaN) semiconductor diode laser as the pump source. The polymer laser was configured as a surface emitting, distributed Bragg reflector laser (DBR), based on a novel energy transfer blend of Coumarin 102 and the conjugated polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene). In this configuration, diode pumping was possible both due to the improved quality of the resonators and the improved harvesting of the diode laser light.
Publisher: IEEE
Date: 2005
Publisher: AIP Publishing
Date: 20-08-2007
DOI: 10.1063/1.2761833
Abstract: A study of the lified spontaneous emission (ASE) properties of three bisfluorene-cored dendrimers in the solid state is reported. The results show that the dendron type has a strong impact on the photoluminescence quantum yield and affects the ASE threshold, the optical gain, and loss coefficients. Optically pumped distributed feedback lasers operating in the blue spectral region were fabricated by spin coating the dendrimer films on top of a two-dimensional corrugated fused silica substrate. A best lasing threshold of 4.5μJ∕cm2 and a slope efficiency of 8.3% were obtained, which demonstrate the high potential of these materials for laser applications.
Publisher: American Chemical Society (ACS)
Date: 12-2003
DOI: 10.1021/MA030383W
Publisher: American Chemical Society (ACS)
Date: 26-09-2006
DOI: 10.1021/CM061173B
Publisher: Wiley
Date: 18-08-2005
Publisher: Wiley
Date: 03-2003
DOI: 10.1889/1.1831700
Publisher: Royal Society of Chemistry (RSC)
Date: 1999
DOI: 10.1039/A902602I
Publisher: Wiley
Date: 09-2005
Publisher: Wiley
Date: 17-09-2013
Publisher: AIP Publishing
Date: 24-06-2003
DOI: 10.1063/1.1586999
Abstract: High-efficiency single-layer-solution-processed green light-emitting diodes based on a phosphorescent dendrimer are demonstrated. A peak external quantum efficiency of 10.4% (35 cd/A) was measured for a first generation fac-tris(2-phenylpyridine) iridium cored dendrimer when blended with 4,4′-bis(N-carbazolyl)biphenyl and electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene at 8.1 V. A maximum power efficiency of 12.8 lm/W was measured also at 8.1 V and 550 cd/m2. These results indicate that, by simple blending of bipolar and electron-transporting molecules, highly efficient light-emitting diodes can be made employing a very simple device structure.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TC00951E
Abstract: Annealing is shown to increase both exciton diffusion and domain size in two organic photovoltaic materials. This enables both efficient light harvesting and efficient charge extraction.
Publisher: Wiley
Date: 12-04-2013
Abstract: An organic semiconductor laser, simply fabricated by UV-nanoimprint lithography (UV-NIL), that is pumped with a pulsed InGaN LED is demonstrated. Molecular weight optimization of the polymer gain medium on a nanoimprinted polymer distributed feedback resonator enables the lowest reported UV-NIL laser threshold density of 770 W cm(-2) , establishing the potential for scalable organic laser fabrication compatible with mass-produced LEDs.
Publisher: AIP Publishing
Date: 11-04-2005
DOI: 10.1063/1.1899256
Abstract: A simple way of tuning the emission color in solution processed phosphorescent organic light emitting diodes is demonstrated. For each color a single emissive spin-coated layer consisting of a blend of three materials, a fac-tris(2-phenylpyridyl)iridium (III) cored dendrimer (Ir–G1) as the green emitter, a heteroleptic [bis(2-phenylpyridyl)-2-(2′-benzo[4,5-α]thienyl)pyridyl]iridium (III) cored dendrimer [Ir(ppy)2btp] as the red emitter, and 4,4′-bis(N-carbazolyl) biphenyl (CBP) as the host was employed. By adjusting the relative amount of green and red dendrimers in the blends, the color of the light emission was tuned from green to red. High efficiency two layer devices were achieved by evaporating a layer of electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI) on top of the spin-coated emissive layer. A brightness of 100cd∕m2 was achieved at drive voltages in the range 5.3–7.3 V. The peak external efficiencies at this brightness ranged from 31cd∕A(18lm∕W) to 7cd∕A(4lm∕W).
Publisher: IOP Publishing
Date: 22-08-2012
Publisher: Wiley
Date: 30-07-2010
Publisher: American Physical Society (APS)
Date: 19-10-2010
Publisher: AIP Publishing
Date: 24-02-2005
DOI: 10.1063/1.1867571
Abstract: We have studied triplet-triplet annihilation in neat films of electrophosphorescent fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3]-cored dendrimers containing phenylene- and carbazole-based dendrons with 2-ethylhexyloxy surface groups using time-resolved photoluminescence. From measured annihilation rates, the limiting current densities above which annihilation would dominate in dendrimer light-emitting devices are found to be & A∕cm2. The triplet exciton diffusion length varies in the range of 2–10 nm depending on the dendron size. The distance dependence of the nearest-neighbor hopping rate shows that energy transfer is dominated by the exchange mechanism.
Publisher: IEEE
Date: 06-2007
Publisher: Elsevier BV
Date: 06-2014
Publisher: Elsevier BV
Date: 06-2008
Publisher: AIP Publishing
Date: 09-03-2009
DOI: 10.1063/1.3098472
Abstract: Effects of different cathode metals, such as aluminum, calcium, and silver, and difference in their reflectivity on the photocurrent generation in pentacene-C60 heterojunction solar cell are presented. Using optical transfer matrix calculations, we find that metal reflectivity has a profound impact on the electrical field confinement within the multilayer device structures. Silver as cathode offers better optical-field confinement close to the pentacene-C60 interface over generally preferred aluminum cathode. External quantum efficiency measurements confirm higher exciton dissociation efficiency and high photocurrent generation ability of silver over aluminum cathode making the choice of cathode metal an important parameter in device optimization.
Publisher: Wiley
Date: 02-07-2007
Publisher: The Optical Society
Date: 10-06-2013
DOI: 10.1364/OE.21.014362
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2PY00519K
Publisher: Elsevier BV
Date: 04-2006
Publisher: American Chemical Society (ACS)
Date: 14-08-2008
DOI: 10.1021/JA8036383
Abstract: Ultrafast luminescence spectroscopy has been undertaken on three iridium cored phosphorescent complexes, with the Ir(ppy)3 molecule being compared with two Ir(ppy)3 cored dendrimers. Energy dissipation by intramolecular vibrational redistribution (IVR) and cooling shows as a luminescence decay because it decreases the admixture of singlet character to the emitting triplet state. A larger amount of vibrational energy dissipates by IVR in dendrimer complexes. We have therefore found a methodology of obtaining unambiguous information on the IVR process and show its potential to study IVR rates as a function of vibrational energy.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Ifor Samuel.