Surface plasmon is a collective oscillation behavior of electrons in metal nanoparticle induced by the excitation of incident light, which can create an enhanced localized electric field near the surface of metal nanoparticle. To date, metal nanoparticle surface plasmon resonances have been extensively studied in the photoluminescence domain; little work however was devoted to electroluminescent and photovoltaic research. In this thesis, as a fundamental study we firstly investigated surface plasmon enhanced europium complex luminescence and obtained an improved understanding of the importance of optical spacer in metal enhanced fluorescence phenomenon. Under this guideline, we incorporated metal NPs into organic light emitting diodes (OLED) and organic solar cells, by means of thermal evaporation and wet chemistry. Metal nanoparticles are demonstrated to enhance the efficiency of both OLEDs and solar cells only under tailored device architecture. The surface plasmon enhanced local electric field plays an important and comprehensive role in enhancing device performance. In Alq3 based OLED we observed increased charge carrier injection by depositing Ag nanoparticles underneath the Al cathode; in Ir(ppy)3 based OLED we gained enhanced luminous efficiency via doping silica functionalized Ag nanoparticles into emitting layer; in P3HT based organic polymer solar cell we noticed an increased polymer absorption by incorporating Ag nanoparticles over the active layer. On the other hand, adverse effects such as metal nanoparticle induced charge carrier recombination and light extinction are also observed. The study of surface plasmon effects in organic optoelectronic devices reveals interesting surface plasmon features and permits to optimize optoelectronic devices from a novel point of view. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-01-05 17:22:40.074

Deep ultraviolet (UV) light sources are useful in a number of applications that include sterilization, medical diagnostics, as well as chemical and biological identification. However, state-of-the-art deep UV light-emitting diodes and lasers made from semiconductors still suffer from low external quantum efficiency and low output powers. These limitations make them costly and ineffective in a wide range of applications. Deep UV sources such as lasers that currently exist are prohibitively bulky, complicated, and expensive. This is typically because they are constituted of an assemblage of two to three other lasers in tandem to facilitate sequential harmonic generation that ultimately results in the desired deep UV wavelength. For semiconductor-based deep UV sources, the most challenging difficulty has been finding ways to optimally dope the (Al,Ga)N/GaN heterostructures essential for UV-C light sources. It has proven to be very difficult to achieve high free carrier concentrations and low resistivities in high-aluminum-containing III-nitrides. As a result, p-type doped aluminum-free III-nitrides are employed as the p-type contact layers in UV light-emitting diode structures. However, because of impedance-mismatch issues, light extraction from the device and consequently the overall external quantum efficiency is drastically reduced. This problem is compounded with high losses and low gain when one tries to make UV nitride lasers. In this thesis, we provide a robust and reproducible approach to resolving most of these challenges. By using a liquid-metal-enabled growth mode in a plasma-assisted molecular beam epitaxy process, we show that highly-doped aluminum containing III-nitride films can be achieved. This growth mode is driven by kinetics. Using this approach, we have been able to achieve extremely high p-type and n-type doping in (Al,Ga)N films with high aluminum content. By incorporating a very high density of Mg atoms in (Al,Ga)N films, we have been able to show, by temperature-dependent photoluminescence, that the activation energy of the acceptors is substantially lower, thus allowing a higher hole concentration than usual to be available for conduction. It is believed that the lower activation energy is a result of an impurity band tail induced by the high Mg concentration. The successful p-type doping of high aluminum-content (Al,Ga)N has allowed us to demonstrate operation of deep ultraviolet LEDs emitting at 274 nm. This achievement paves the way for making lasers that emit in the UV-C region of the spectrum. In this thesis, we performed preliminary work on using our structures to make UV-C lasers based on photonic crystal nanocavity structures. The nanocavity laser structures show that the threshold optical pumping power necessary to reach lasing is much lower than in conventional edge-emitting lasers. Furthermore, the photonic crystal nanocavity structure has a small mode volume and does not need mirrors for optical feedback. These advantages significantly reduce material loss and eliminate mirror loss. This structure therefore potentially opens the door to achieving efficient and compact lasers in the UV-C region of the spectrum.

Light-emitting diode (LED) is an improved light delivery technology that provides better energy efficiency, longer lifespan, and the ability to select a specific wavelength of light. We evaluated the effect of blue and red-LED on performance, behavior, egg quality, hormonal concentration, and prevalence of Avian pathogenic E. coli (APEC) like E. coli in pullets and laying hens raised in cageree housing system. Results showed that birds raised in blue-LED during the pullet phase had higher body weight and earlier onset of early lay. Red-LED increased the yolk percentage, illustrating that red-LED can stimulate reproduction. Red-LED also decreased the relative spleen percentage, which is an indication of decreased immunity. Overall egg production was not affected by the light treatment. Irrespective of the light treatment, a higher prevalence of APEC like E. coli was found in colonies isolated from the trachea suggesting a possible route of transmission in cageree housing system.

Submitted by Nadir Basilio (nadirsb@uninove.br) on 2018-06-21T18:42:55Z No. of bitstreams: 1 Heliodora Leao Casalechi.pdf: 2679810 bytes, checksum: f981677bdc05834caca5e26029e42566 (MD5) / Made available in DSpace on 2018-06-21T18:42:55Z (GMT). No. of bitstreams: 1 Heliodora Leao Casalechi.pdf: 2679810 bytes, checksum: f981677bdc05834caca5e26029e42566 (MD5) Previous issue date: 2015-06-24 / Tendinitis is a common disorder of the musculoskeletal system with multiple pathological manifestations. Although most tendons have the ability to spontaneously repair after injury, scar tissue is formed that can prevent the tendon to perform normal functions. Studies have been conducted using phototherapy in different health areas, using low-intensity lasers and LEDs. However, there are few studies with LEDs therapy. The aim of this study was to investigate the effect of phototherapy with Laser (830nm) and LED (945nm) in the repair process of the calcaneus tendonitis in rats. The inflammation was induced by controlled contusion in the medial region of the Achilles tendon of the animals. Was used 112 young male Wistar rats (240 ± 20g), divided into 14 groups with two different experimental periods. Groups CONT (control group), TEND (tendinitis group) during periods 7 and 14 days, LEDT (LED therapy, from th to 7th day and from 1th to 14th day), and LEDT delay (LED therapy from 7th to 14th day). The therapy was initiated 12h after the tendinitis induction, with a 48h interval between irradiations (dose 6J/point). The control animals received simulation of treatment; the same experimental design was used for Laser treatment. All groups were euthanized on the 7th or 14th day after the induction. The tendons were dissected, extracted, and sent for analysis. Were performed biomechanical and histological analysis to evaluate neutrophils and collagen, were also quantitated the inflammatory mediators by real-time polymerase chain reaction (RT-PCR) and the IL-6 and TNF- α levels by ELISA. The results showed that treatments with low-intensity lasers in the parameters used and the times studied reduces migration of inflammatory cells and improves the quality of repair, but the LED even decreasing the inflammation was not effective of biomechanical properties of tendon tissue. / A tendinite é uma desordem comum do sistema musculoesquelético. Embora os tendões tenham habilidade de reparação espontânea após ferimento, o tecido da cicatrização que é formado pode impedir o tendão de executar as funções normais. Estudos vêm sendo realizados utilizando a fototerapia em diferentes áreas da saúde, empregando tanto laseres quanto LEDs de baixa intensidade. Contudo, existe um número reduzido de estudos com a utilização da terapia com LEDs. O objetivo deste estudo foi investigar os efeitos anti-inflamatórios e as propriedades mecânicas do tecido após a ação da fototerapia utilizando LASER (830nm) e LEDs (945nm), na região do infravermelho, na tendinite induzida por trauma mecânico em tendão de Aquiles de ratos. Foram utilizados 112 ratos machos albinos da linhagem Wistar (240 ± 20g), distribuídos em 14 grupos e dois períodos experimentais diferentes. Grupos CONT (grupo controle), os grupos TEND (grupos tendinite) nos períodos de 7 e 14 dias, o LEDT (grupos terapia LED), do 1º ao 7º dia e do 1º ao 14º dia) e o grupo LEDT delay (terapia LED do 7º ao 14º dia). A terapia teve início 12 horas após a indução da tendinite, utilizando uma dose de 6J no ponto de aplicação, com intervalos de 48 em 48 horas. A fototerapia foi aplicada transcutaneamente em um único ponto sobre a região lesionada. Os animais dos grupos controle foram submetidos à simulação da aplicação com o aparelho desligado, o mesmo desenho experimental foi utilizado feito para o tratamento Laser. As eutanásias ocorreram ao 7º e 14º dia do experimento. Foi realizada análise biomecânica, histopatológica para avaliação de neutrófilos e colágeno, também foram quantificados os mediadores inflamatórios por meio da RT-PCR e os níveis de IL-6 e TNF- α foram avaliados pelo teste imunoenzimático (ELISA). Por meio dos resultados encontrados, é possível inferir que os tratamentos com Laser de baixa intensidade, nos parâmetros utilizados e nos tempos estudados melhora a qualidade do reparo do tecido tendíneo, a biomecânica e reduz a migração de células inflamatórias, já o LED de baixa intensidade apesar de diminuir a inflamação não foi eficiente na manutenção da biomecânica do tendão.

The use of photonic crystals for light extraction from light-emitting diodes (LEDs) gives the possibility to shape the farfield emission pattern. This is of particular interest for étendue-limited LED applications that require a more directional farfield than state- of-the-art Lambertian emitters. However, the application of a photonic crystal in a LED results in directional emission only if the photonic crystal and the distribution of guided modes in the LED are tuned correctly. In this thesis, red- and blue-emitting thin-film PhC-LEDs in the AlGaInP and InGaN material systems were modelled, designed, fabricated and characterized. The first experimental results show that light extraction with photonic crystals from AlGaInP thin-film LEDs several microns thick is neither directional nor more efficient than state-of-the-art LEDs with a rough surface structure. Directional light extraction for AlGaInP PhC-LEDs is for the first time demonstrated in much thinner devices where the photonic crystal light extraction of guided modes is combined with the resonant-cavity effect. In an attempt to approach the ideal PhC-LED, strong photonic crystal farfield shaping is demonstrated in InGaN thin-film LEDs of sub-micron thickness. Analysis of their spectral farfields unexpectedly shows that high order diffraction contributes significantly to the light extraction efficiency if the mode absorption is sufficiently low. It is also demonstrated that directional photonic crystal light extraction is possible in InGaN thin-film LEDs several microns thick. The directionality stems from the modulation of the spontaneous emission caused by the proximity of the active region to the bottom mirror. Two new concepts for enhanced light extraction and high directionality are presented: Photonic crystals with two dominating lattice constants are found to outperform conventional photonic crystal LEDs. An alternative approach is the dielectric PhC-LED - FDTD simulations show that the high extraction efficiency of LEDs with surface roughness is combined with the higher directionality of photonic crystal light extraction.

InGaN heterostructures are at the core of blue light emitting diodes (LEDs) which are the basic building blocks for energy efficient and environment friendly modern white light generating sources. Through quantum confinement and electronic band structure tuning on the opposite end of the spectrum, Ge1−xSnx alloys have recently attracted significant interest due to its potential role as a silicon compatible infra-red (IR) optical material for photodetectors and LEDs owing to transition to direct bandgap with increasing Sn. This thesis is dedicated to establishing an understanding of the optical processes and carrier dynamics in InGaN heterostructures for achieving more efficient visible light emitters and terahertz generating nanocavities and in colloidal Ge1−xSnx quantum dots (QDs) for developing efficient silicon compatible optoelectronics. To alleviate the electron overflow, which through strong experimental evidence is revealed to be the dominating mechanism responsible for efficiency degradation at high injection in InGaN based blue LEDs, different strategies involving electron injectors and optimized active regions have been developed. Effectiveness of optimum electron injector (EI) layers in reducing electron overflow and increasing quantum efficiency of InGaN based LEDs was demonstrated by photoluminescence (PL) and electroluminescence spectroscopy along with numerical simulations. Increasing the two-layer EI thickness in double heterostructure LEDs substantially reduced the electron overflow and increased external quantum efficiency (EQE) by three fold. By incorporating δ p-doped InGaN barriers in multiple quantum well (MQW) LEDs, 20% enhancement in EQE was achieved due to improved hole injection without degrading the layer quality. Carrier diffusion length, an important physical parameter that directly affects the performance of optoelectronic devices, was measured in epitaxial GaN using PL spectroscopy. The obtained diffusion lengths at room temperature in p- and n-type GaN were 93±7 nm and 432±30 nm, respectively. Moreover, near field scanning optical microscopy was employed to investigate the spatial variations of extended defects and their effects on the optical quality of semipolar and InGaN heterostructures, which are promoted for higher efficiency light emitters owing to reduced internal polarization fields. The near-field PL from the c+ wings in heterostructures was found to be relatively strong and uniform across the sample but the emission from the c- wings was substantially weaker due to the presence of high density of threading dislocations and basal plane stacking faults. In case of heterostructures, striated regions had weaker PL intensities compared to other regions and the meeting fronts of different facets were characterized by higher Indium content due to the varying internal field. Apart from being the part and parcel of blue LEDs, InGaN heterostructures can be utilized in generation of coherent lattice vibrations at terahertz frequencies. In analogy to LASERs based on photon cavities where light intensity is amplified, acoustic nanocavity devices can be realized for sustaining terahertz phonon oscillations which could potentially be used in acoustic imaging at the nanoscale and ultrafast acousto-optic modulation. Using In0.03Ga0.97N/InxGa1-xN MQWs with varying x, coherent phonon oscillations at frequencies of 0.69-0.80 THz were generated, where changing the MQW period (11.5 nm -10 nm) provided frequency tuning. The magnitude of phonon oscillations was found to increase with indium content in quantum wells, as demonstrated by time resolved differential transmission spectroscopy. Design of an acoustic nanocavity structure was proposed based on the abovementioned experimental findings and also supported by full cavity simulations. Optical gap engineering and carrier dynamics in colloidal Ge1−xSnx QDs were investigated in order to explore their potential in optoelectronics. By changing the Sn content from 5% to 23% in 2 nm-QDs, band-gap tunability from 1.88 eV to 1.61 eV, respectively, was demonstrated at 15 K, consistent with theoretical calculations. At 15 K, time resolved PL spectroscopy revealed slow decay (3 − 27 μs) of luminescence, due to recombination of spin-forbidden dark excitons and effect of surface states. Increase in temperature to 295 K led to three orders of magnitude faster decay (9 − 28 ns) owing to the effects of thermal activation of bright excitons and carrier detrapping from surface states. These findings on the effect of Sn incorporation on optical properties and carrier relaxation and recombination processes are important for future design of efficient Ge1−xSnx QDs based optoelectronic devices. This thesis work represents a comprehensive optical study of InGaN heterostructures and colloidal Ge1−xSnx QDs which would pave the way for more efficient InGaN based LEDs, realization of terahertz generating nanocavities, and efficient Ge1−xSnx based silicon compatible optoelectronic devices.

Master of Science / Department of Architectural Engineering and Construction Science / Fred Hasler / This paper discusses the color rendition capabilities of light emitting diodes (LEDs) and their relationship with the current standard for color rendition quality. The current standard for judging light source color rendering properties, known as the color rendering index (CRI), has come under heavy scrutiny in recent years with the introduction of LED in commercial lighting applications. LEDs, depending on construction type, have highly structured spectral distributions which do not scale well under the color rendering index; moreover, CRI for LEDs has become disjointed with the subjective measurement of human color preference. Unfortunately, given the multidimensional nature of color, an all-encompassing scale with a single rated value for color rendition capabilities of a light source has proven difficult to establish. An analysis on the human visual system is first discussed, establishing how the visual system first detects color in the eye and subsequently encodes that color information through a color-opponent process, formulating conscious color appearance. The formation of color appearance leads into a discussion on human color vision and the creation of three dimensional color space, which is subsequently used for the measurement of color fidelity (CRI) of consumer light sources. An overview of how LED lamps create light and color is then discussed, showing that the highly structured spectral distribution of LED lamps is often the cause of discrepancy within the CRI system. Existing alternatives to the CRI system are then compared and contrasted to each other, and the existing CRI system. A final color preference study was conducted where four LED lamps where compared to a reference lamp of equal correlated color temperature. Observers were asked to rate the various test lamps against the reference lamp in terms of vividness, naturalness, overall preference, and individual color preference. It was found that no significant difference was found between the first three dimensions measured but significant trend lines existed for the preference of individual colors when illuminated by either LED lamps or the reference source. Recommendations are then made for how the lighting industry could move forward in terms of color metrics.

Master of Science / Department of Animal Sciences and Industry / Elizabeth A. E. Boyle / Light emitting diode (LED) and fluorescent (FLS) lighting effects on enhanced pork loin chops, beef longissimus dorsi and semimembranosus steaks, ground beef, and ground turkey displayed in two retail display cases set up with similar operational temperatures were evaluated using visual and instrumental color, Enterobacteriaceae (EB) and aerobic plate counts (APC), internal product and case temperatures, and thiobarbituric acid reactive substances (TBARS). Visual discoloration of the five meat products increased (P<0.05) as display time increased. Beef longissimus dorsi steaks, ground beef, and the superficial portion of beef semimembranosus steaks had less (P<0.05) visual discoloration under LED lighting than FLS. Compared to FLS, pork loin chops under LED lighting had higher (P<0.05) L* values and a lower (P<0.05) a/b ratio. The deep portion semimembranosus steak under LED was redder (P<0.05) and the superficial portion had a lower (P<0.05) a/b ratio; LED deep and superficial portion semimembranosus steaks had higher (P<0.05) saturation index values at 5.18 and 4.47, respectively, on d 0 than FLS. Pork chops under LED lighting had lower (P<0.05) APC populations than FLS by the end of display. Enterobacteriaceae populations fluctuated throughout display on ground turkey under FLS lighting while populations remained stable under LED. APC populations increased as display time increased for pork loin chops, ground beef and ground turkey, but not beef longissimus dorsi steaks possibly due to initial case-ready postmortem age. As display time increased, EB populations increased (P<0.05) for pork loin chops, ground beef and ground turkey. The internal temperature of all products, except beef longissimus dorsi steaks, was lower (P<0.05) in the LED case. FLS case temperatures were higher (P<0.05) by 0.56 to 1.11°C than LED over the duration of the study. Pork loin chops, ground turkey, and beef semimembranosus steaks had higher (P<0.05) TBARS values by 0.06 to 0.24 mg malonaldehyde/kg under LED lighting, but lighting type did not affect (P>0.05) lipid oxidation of beef longissimus dorsi steaks or ground beef. LED lighting results in lower display case temperatures, lower internal product temperatures, and extended color life; however, lipid oxidation was increased in some cuts under LED lighting.

Au cours de cette thèse, nous avons synthétisé de nouveaux composés en utilisant des macrocycles de porphyrines comme socle pour nos architectures. L'objectif était d'étudier leurs propriétés en optique linéaire et non linéaire. Plus précisément, nous avons synthétisé et caractérisé trois groupes de dendrimères de type fluorényl-porphyrine, une série de porphyrines organométalliques dérivés du ruthénium, et commencé une dernière série de nouvelles porphyrines. Les corrélations entre les propriétés et la structure ont été étudiés, le processus de transfert d'énergie du donneur vers la porphyrine a aussi été évalué. En introduction, nous avons présenté le contexte général de la chimie des porphyrines basé sur quatre aspects: (1) la structure chimique, (2) les voies de synthèse, (3) les propriétés en optique linéaire (4) et en optique non linéaire. Nous avons ensuite présenté les différents travaux qui ont été effectués dans notre groupe, et conclut en proposant de nouvelles structures basées sur ces résultats. Dans le premier chapitre, nous présentons la synthèse d'un groupe de dendrimères dérivés de thiényl-porphyrines. Les unités thiényles font le pont entre les dendrons conjugués de type fluorényle et le coeur de la porphyrine. Le transfert d'énergie pour ces molécules est efficace et ces dernières présentent des propriétés en optique non linéaire qui sont intéressantes avec une amélioration de l'absorption à deux photons (ADP). Dans le deuxième chapitre, nous présentons la synthèse d'une série de composés à base de ruthénium dérivés de la Tétrafluorényl- porphyrine (TFP), pour des applications en optique non linéaire (üNL). Dans le troisième chapitre, nous présentons la synthèse de deux nouveaux dendrons avec des antennes fluorényles terminales greffées en position 9 d'un troisième fluorényle, respectivement par voie conjuguées ou non conjuguées. Puis deux nouveaux dendrimères ont été obtenus par couplage de Sonogashira à partir de ces dendrons sur le coeur porphyrine TFP. Le transfert d'énergie de ces dendrons vers la porphyrine est efficace. Ces molécules présentent des propriétés en optique non linéaire qui sont intéressantes et les résultats en ADP sont très prometteurs. Dans le quatrième chapitre, nous présentons la synthèse de porphyrines avec des bras fluorénones terminales. Ces porphyrines émettent également une luminescence rouge et le transfert d'énergie est très efficace. Comme perspectives, un nouveau type de porphyrine méso-alcynyle est envisagé, pour l' instant nous avons juste synthétisé la génération 0 de cette série de dendrimères: Les quatre bras tluorényles sont pontés au coeur de la porphyrine avec des liens alcynyles, et les études optiques de ces prototypes sont en cours. / During this thesis, we have elaborated new compounds using the porphyrin macrocycle as the basic platform of our architectures. The aim, after their syntheses, was to study the linear optical (LO) and non-linear optical (NLO) properties of these new molecules. More precisely, we have synthesized and characterized three groups of fluorenyl-porphyrin dendrimers, a series of ruthenium organometallic porphyrins, and started a series of new type of porphyrin. Their correlations on optical property-structure have been discussed, as well as the energy transfer processes from the donor fragments to porphyrin core acceptor. In the introduction, we presented the general background of the porphyrin chemistry based on four aspects: ( I) structure, (2) synthetic methods, (3) LO properties and (4) NLO properties. We further reviewed prior porphyrin studies done in our group and proposed new molecular designs based on these results. In the first chapter, we synthesized a group of thienyl porphyrin cored dendrimers. The thienyl units connect the conjugated fluorenyl dendrons to porphyrin ring by alkynyl bridges. The energy transfer (ET) of these porphyrins is very efficient and they present interesting NLO properties with enhanced Two-photon absorption (TPA). In the second chapter, we synthesized a series of ruthenium compounds based on Tetra-fluorenyl porphyrin core (TFP) for NLO applications. In the third chapter, we synthesized two new dendrons with two terminal fluorenyl antennae fi xed on the 9 position of the fluorenyl units in conjugated or non-conjugated way respecti vely. Then two new porphyrin dendrimers were obtained by Sonogashira coupling reaction of these dendrons on TFP porphyrin core. Their ET from dendrons to porphyrin core is very efficient. They present interesting LO properties and the TPA results are very promising. In the fourth chapter, we synthesized a group of TFP cored porphyrins with terminal fluorenone anns. These porphyrins emit red luminescence and the ET is very efficient from the linear arms toward their cores. As perspective, a new type of meso-alkynyl porphyrin series is considered, for the moment we synthesized only the generation 0 of the dendrimers: the four fluorenyl arms of this porphyrin are bridged to the centre ring by alkynyl chains, and the optical studies of this prototype are in progress.

One of the major challenges in the field of organic semiconductors is to develop molecular design rules and processing routes which optimise the charge carrier mobility, whilst independently controlling the radiative and non-radiative processes. To date there has existed a seeming trade-off between charge carrier mobility and photoluminescence efficiency, which limits the development of some devices such as electrically pumped laser diodes. This thesis investigates fluorescence enhancement strategies for high-mobility polymer semiconductor systems and the mechanisms by which they currently display poor emission properties. Four independent approaches were taken and are detailed as follows. 1. Solubilising chain engineering It is shown that for the high mobility polymer poly(indacenodithiophene-co-benzothiadiazole), the addition of a phenyl- initiated side chain can enhance the solid-state fluorescence quantum yield, exciton lifetime and exciton diffusion length significantly in comparison to that without phenyl-addition. 2. Energy transfer to a highly fluorescent chromophore It is shown that for the high mobility polymer poly(indacenodithiophene-co-benzothiadiazole) efficient energy transfer to a more emissive squaraine dye molecule is possible despite fast non-radiative decay short exciton diffusion lengths. This results in a significant fluorescence enhancement, which in turn facilitates an order of magnitude increase of the efficiency of polymer light emitting diodes made from this material combination. 3. Energy gap engineering The well known Energy Gap Law predicts an increase in the non-radiative rate as the optical bandgap of an organic chromophore decreases in energy. In combination with this, almost all polymer semiconductors reported to date with high charge carrier mobility have low optical bandgaps. Therefore, molecular design principles which act to increase the optical bandgap of polymer semiconductors whilst retaining a high mobility were sought out. One specific system was successfully identified and showed a significant fluorescence enhancement compared to is predecessor poly(indacenodithiophene-co-benzothiadiazole) in both the solution and the solid state. It is found that the Frenkel exciton lifetime in this new system is a factor of four larger which also results in a significantly increased exciton diffusion length. An inter-chain electronic state is also identified and discussed. 4. Hydrogen substitution For some low-bandgap material systems such as erbium chromophores, high energy vibrational modes such as the C-H stretching mode can act as non-radiative pathways. The effect of hydrogen substitution with deuterium and fluorine was therefore investigated in a series of polythiophene derivative families. It was found that in the solid state, fluorescence and exciton lifetime enhancement occurred when the backbone hydrogen atoms were replaced with fluorine. However, evidence is given that this was not owing to the initial hypothesis, and is more likely owing to structural differences which occur in these substituted material systems.