Filmes finos de nitreto de silício com excesso de nitrogênio foram depositados sobre silício por sputtering reativo para obter estruturas emissoras de luz. As amostras foram modificadas por implantação iônica para verificar a influência dos dopantes arsênio (As) e boro (B) nos espectros de fotoluminescência (PL). As medidas de PL foram realizadas na faixa de temperatura entre 15-300 K e apresentaram uma emissão entre os comprimentos de onda 370-870 nm. Os dopantes introduziram uma emissão em 725 nm na banda de emissão, principalmente as dopadas com As. Foram realizadas medidas de microscopias para verificar a presença de nanoestruturas assim como a distribuição dos dopantes no material. As imagens de microscopias confirmaram a presença de nanocristais de nitreto de silício nas fases α, β e γ e identificaram a presença do dopante B nas fases cristalinas. O modelo de condução de Pool-Frenkel domina o transporte de portadores, indicando que a condução ocorre pelos níveis intrabandas, característica que definiu o modo que as recombinações radiativas ocorreram. As medidas de eletroluminescência (EL) apresentaram uma emissão centrada nos comprimentos de onda 760 e 880 nm (polarização negativa) e 1010 nm (polarização positiva) revelando diferenças significativas quando comparadas com as medidas de PL. Essa diferença esta associada à maneira como os elétrons populam os níveis intrabanda (excitação óptica para PL e elétrica para EL) que resulta em recombinações radiativas em diferentes comprimentos de ondas. A intensidade dos espectros de EL manifestou uma dependência quase linear com a densidade de corrente para ambas as polarizações. As medidas de EL em campos alternados exibiram um espectro de emissão composto pela soma das bandas obtidas separadamente em cada uma das polarizações. Medidas de EL em diferentes temperaturas (50-300 K) foram realizadas para investigar a influência da temperatura nos processos de recombinação radiativa. A intensidade exibiu uma redução com o aumento da temperatura, devido ao aumento do acoplamento elétron-fônon. / Silicon nitride with excess of nitrogen thin films were deposited on silicon substrate by reactive sputtering in order to obtain light emitting structures. Samples were modified by ion implantation of arsenic (As) and boron (B) to ascertain dopant leverage at photoluminescence (PL) spectra. PL measurements were performed at temperature ranging from 15 K up to 300 K and showed a band emission between wavelength 370 and 870 nm. An emission centered at 725 nm was observed in doped samples; especially in the presence of As. Microscope images showed crystalline structures of α-Si3N4, β-Si3N4 and γ-Si3N4 and confirmed boron dopant in nanocrystalline structures. Pool-Frenkel conduction model dominates electron transport in non-stoichiometric silicon nitride films due to intraband levels, phenomenon that has a huge contribution to electroluminescence (EL) emission. EL signals were composed by two peaks centered at 760 and 880 nm (negative bias – EL-N) and one peak at 1010 nm (positive bias – EL-P). Diffences between PL and EL spectra exhibit a clear dependence on the mode of excitation (photo and current source) on radiative recombination process. EL intensity had almost a linear increase with current density for both polarizations. EL measurements under AC voltage were composed by a superposition of the signals from EL-N and EL-P signals. Photo and electroluminescence measurements were collected at different temperatures (50 to 300 K) in order to investigate the temperature influence on the radiative recombination. The EL intensity was decreasing with temperature increasing, due to electron-phonon interactions.

In this thesis, optical studies of c-plane InGaN/GaN quantum well (QW) structures are presented. The effects of a Si-doped underlayer (UL) on the optical properties of multiple quantum well (MQW) structures are investigated. The QW photoluminescence (PL) emission peak energy and radiative recombination rate decrease and increase respectively with increasing number of QWs. These observations are attributed to the increasing net electric field across the MQW structure as the strength of the surface polarisation field, which acts in the opposite sense to the piezoelectric polarisation fields across the QWs, reduces with increasing distance of the UL from the sample surface. This leads to a reduction in the electron-hole recombination energy and wavefunction overlap. It is also shown that the internal quantum efficiency of the MQW structures may decrease with increasing number of QWs due to the reducing radiative recombination rate, which could indicate that carrier losses due to thermionic emission or interface recombination are mitigated by the inclusion of an UL. Optical studies of single QW structures containing Si-doped ULs with different net electric fields across the QW are presented. The net electric field across the QW is changed by varying the thickness of the GaN cap layer. The full width at half maximum of the emission peak increases with increasing net electric field across the QW. This is attributed to the increasing variation in electron ground state energies due to the role of the electric field in the localisation of electrons at quantum well width fluctuations. For one sample, a smaller Huang-Rhys factor compared to the rest of the samples is calculated. The non-exponential PL decays detected on the low energy side of the QW emission peak from this sample are also of a different shape to the other PL decays detected at all energies for the other samples. This may be due to the reversal of the net electric field across these QW regions. Observations of a broad emission band on the high energy side of single QW structures at high excited carrier densities are presented. This band occurs in the carrier density regime at which the efficiency droop is observed. The emission band is attributed to higher energy weakly localised or delocalised electron and hole states that are populated following the saturation of the localised ground states. PL decay curves detected across this emission band exhibit plateaus where the PL intensity remains constant until the higher energy emission has decayed. These are similar to decays observed in semiconductor quantum dots, which are characteristic of Pauli state blocking.

Chow Chi Fai. / Thesis submitted in: August 2005. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract / Abstract (Chinese) / A cknowledgements / Table of Contents / List of Figures / List of Tables / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- The need for light emission from silicon --- p.1-1 / Chapter 1.2 --- Silicon-based light emitting material 1 - --- p.2 / Chapter 1.3 --- Literature overview --- p.1-4 / Chapter 1.4 --- Project goal --- p.1-10 / Reference --- p.1-11 / Chapter Chapter 2 --- Experimental details / Chapter 2.1 --- Introduction --- p.2-1 / Chapter 2.2 --- Sample preparation techniques --- p.2-1 / Chapter 2.2.1 --- MEVVA ion implantation --- p.2-1 / Chapter 2.2.2 --- PL samples preparation conditions --- p.2-3 / Chapter 2.2.3 --- EL samples preparation conditions --- p.2-4 / Chapter 2.3 --- Characterization techniques --- p.2-7 / Chapter 2.3.1 --- Photoluminescence spectroscopy (PL) --- p.2-7 / Chapter 2.3.2 --- Electroluminescence spectroscopy (EL) --- p.2-9 / Chapter 2.3.3 --- Rutherford backscattering spectroscopy (RBS) --- p.2-10 / Chapter 2.3.4 --- X-ray diffraction (XRD) --- p.2-12 / Chapter 2.3.5 --- Transmission electron microscopy (TEM) --- p.2-13 / Reference --- p.2-15 / Chapter Chapter 3 --- Resutls and Discussions / Chapter 3.1 --- RBS results --- p.3-1 / Chapter 3.2 --- XRD results --- p.3-8 / Chapter 3.3 --- TEM results --- p.3-12 / Chapter 3.3.1 --- Effects of the implantation energy on the microstructure of samples --- p.3-13 / Chapter 3.3.2 --- Effects of the implantation dose on the microstructure of samples --- p.3-16 / Chapter 3.4 --- Photoluminescence results --- p.3-19 / Chapter 3.4.1 --- Effect of implantation energy on the PL --- p.3-19 / Chapter 3.4.2 --- Effect of FA temperature on the PL --- p.3-24 / Chapter 3.4.3 --- Effect of FA duration on the PL --- p.3-26 / Chapter 3.4.4 --- Effect ofRTA duration on the PL --- p.3-28 / Chapter 3.4.5 --- Effect ofRTA temperature on the PL --- p.3-30 / Chapter 3.4.6 --- Effect of implantation dose on the PL --- p.3-32 / Chapter 3.4.7 --- Si band edge enhancement --- p.3-34 / Chapter 3.4.8 --- Photoluminescence spectra as a function of excitation power density --- p.3-37 / Chapter 3.4.9 --- Photoluminescence spectra as a function of measurement temperature --- p.3-45 / Chapter 3.5 --- Electroluminescence results --- p.3-52 / Chapter 3.5.1 --- EL quantum efficiency --- p.3-60 / Reference --- p.3-61 / Chapter Chapter 4 --- Conclusion and future works / Chapter 4.1 --- Conclusion --- p.4-1 / Chapter 4.2 --- Future works --- p.4-2 / Appendix I / Appendix II

Le contrôle des propriétés et la maîtrise du couplage cohérent d'objets quantiques individuels dans une matrice solide sont un enjeu essentiel pour le développement de l'information quantique. Les centres colorés dans le diamant, équivalent aux molécules artificielles, présentent des caractéristiques qui sont très prometteuses pour la réalisation d'une telle application. Parmi les centres colorés, le centre NV (azote-lacune) est le plus intéressant, dû en particulier à sa grande photostabilité à température ambiante. Le travail de cette thèse est consacré à l'étude des propriétés optiques et électroniques des centres colorés NV à température ambiante. / Researches over the past decade in many fields of science, including physics, chemistry have initiated the dream of building computers that work according to the rules of quantum mechanics, and computer and quantum information have been proposed. The Nitrogen-Vacancy color center in diamond is one of the most promising candidate due to several advantages: no blinking and no photo bleach at room-temperature, single photon generation, electron spin manipulated with microwave and readout optically. This thesis concentrates on the study of optical and spin properties of NV color center.

by Ng Po Yin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 57-59). / by Ng Po Yin. / Acknowledgments --- p.I / Abstract --- p.II / Table of contents --- p.III / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Interest in ZnxCd1-xSe/InP --- p.1 / Chapter 1.2 --- Our work --- p.2 / Chapter 1.3 --- Usefulness of PL --- p.4 / Chapter 1.4 --- Growth conditions of ZnSe/GaAs and ZnxCd1-x/InP --- p.4 / Chapter 1.5 --- Purposes of studying ZnSe/GaAs --- p.5 / Chapter 1.6 --- Inhomogeneity of ZnxCd1-xSe/InP --- p.5 / Chapter Chapter 2 --- Experimental setup and procedures --- p.7 / Chapter 2.1 --- Experimental setup --- p.7 / Chapter 2.2 --- Measurements performed --- p.10 / Chapter 2.3 --- Experimental procedures --- p.10 / Chapter Chapter 3 --- Results and discussion --- p.12 / Chapter 3.1 --- RT and 9K PL of ZnSe/GaAs --- p.12 / Chapter 3.2 --- "Excitation power density dependent, RT and 9K PL of ZnxCd1-xSe/InP" --- p.20 / Chapter 3.3 --- Temperature dependent PL of ZnSe/GaAs and ZnxCd1-xSe/InP --- p.45 / Chapter Chapter 4 --- Conclusions and future work --- p.55 / References --- p.57

Iu Kwan Sai = 以光致發光譜和高解析度X射線衍射譜研究砷銻化鎵外延層和量子井 / 姚昀樨. / On t.p. "̳x" is subscript. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 93-95). / Text in English; abstracts in English and Chinese. / Iu Kwan Sai = Yi guang zhi fa guang pu he gao jie xi du X she xian yan she pu yan jiu shen ti hua jia wai yan ceng he liang zi jing / Yao Yunxi. / ACKNOWLEDGMENTS --- p.i / ABSTRACT --- p.ii / TABLE OF CONTENTS --- p.v / LIST OF TABLES --- p.vii / LIST OF FIGURES --- p.viii / Chapter 1. --- INTRODUTION --- p.1 / Chapter 1.1 --- Motivations --- p.1 / Chapter 1.2 --- Historical Works --- p.1 / Chapter 1.3 --- This Study --- p.3 / Chapter 1.4 --- Growth Conditions of GaAs1-xSbx Alloy --- p.4 / Chapter 2. --- EXPERIMENTAL PROCEDURES --- p.5 / Chapter 2.1 --- High Resolution X-Ray Diffraction (HRXRD) --- p.5 / Chapter 2.1.1 --- The Use of HRXRD --- p.5 / Chapter 2.1.2 --- Setup of the High Resolution X-Ray Diffractometer --- p.7 / Chapter 2.1.3 --- Types of Measurements --- p.8 / Chapter 2.2 --- Photoluminescence (PL) Spectrometer --- p.10 / Chapter 2.2.1 --- The Use of PL --- p.10 / Chapter 2.2.2 --- Setup of PL spectrometer --- p.10 / Chapter 2.2.3 --- types of Measurements --- p.13 / Chapter 3. --- CHARACTERIZATION --- p.14 / Chapter 3.1 --- High Resolution X-Ray Diffraction (HRXRD) --- p.14 / Chapter 3.1.1 --- Principal Scattering Geometries --- p.14 / Chapter 3.1.2 --- Strains in the Epitaxial Layer --- p.16 / Chapter 3.1.3 --- Lattice Parameter --- p.21 / Chapter 3.1.4 --- Sb Composition --- p.24 / Chapter 3.1.5 --- Determination of Thickness --- p.24 / Chapter 3.2 --- Photoluminescence (PL) --- p.25 / Chapter 3.2.1 --- Basic Theory of PL --- p.25 / Chapter 3.2.2 --- Strain and Temperature Effect --- p.26 / Chapter 3.2.3 --- Type I and Type II PL --- p.27 / Chapter 3.2.4 --- The Energy Gap of GaAs1-xSbx --- p.28 / Chapter 4. --- RESULTS AND DISCUSSION --- p.31 / Chapter 4.1 --- Direct Analysis of HRXRD Rocking Curves --- p.31 / Chapter 4.1.1 --- GaAs1-xSbx / GaAs Quantum Wells (QWs) --- p.31 / Chapter 4.1.2 --- GaAs1-xSbx /InP Epitaxial Layers --- p.42 / Chapter 4.2 --- Computer Simulation of HRXRD --- p.51 / Chapter 4.2.1 --- Simulation Theory --- p.51 / Chapter 4.2.2 --- Simulation of Rocking Curves --- p.51 / Chapter 4.3 --- Room Temperature PL of GAAs1-xSBx Quantum Wells and Epitaxial Layers --- p.66 / Chapter 4.4 --- Low Temperature (LT) PL of GAAs1-xSBx Quantum Wells and Epitaxial Layers --- p.75 / Chapter 4.5 --- Excitation Power Dependent (PD) PL of GAAs1-xSBx Quantum Wells and Epitaxial Layers --- p.78 / Chapter 4.6 --- Temperature Dependent (TD) PL of GAAs1-xSBx Quantum Wells and Epitaxial Layers --- p.85 / Chapter 5. --- CONCLUSIONS --- p.90 / REFERENCES --- p.93

Neste trabalho foram preparadas as amostras Al2O3:TR3+ (TR3+=Eu, Gd) pelos métodos cerâmico, combustão e Pechini, calcinadas de 400 - 1400 ºC. Os difratogramas de raios X sugerem que as amostras calcinadas em menores temperaturas apresentam-se como sistemas amorfos, que com a elevação da temperatura de calcinação transformam-se na fase cúbica das aluminas ativadas (γ-Al2O3). A partir de 1200 ºC forma-se a fase hexagonal de α-Al2O3, altamente cristalina e termoestável. O tamanho dos cristalitos foi determinado pelo método de Scherrer a partir dos respectivos difratogramas. Em geral, os espectros no infravermelho de Al2O3:Eu3+ apresentaram estiramentos relativos aos grupos tetraédricos [AlO4] condensados e/ou isolados indicando a presença de fase γ-alumina. Foi também observada a existência de bandas em regiões de menores energias atribuídas às freqüências de estiramento de grupos octaédricos [AlO6] relativas à fase α-alumina (coríndon). A Microscopia Eletrônica de Varredura (MEV) indicou que as partículas obtidas pelo método cerâmico apresentam menor tamanho e uma morfologia mais uniforme comparados com aquelas obtidas pelos métodos de combustão e Pechini. Os espectros de emissão (λ exc. = 320 nm) do sistema Al2O3:Gd3+ não apresentam as bandas finas oriundas dos íons Cr3+ observadas nos espectros da alumina não dopada, indicando que íon Gd3+ suprime a luminescência destes íons. Os espectros de excitação das amostras Al2O3:Eu3+ preparadas pelo três métodos apresentam uma banda larga atribuída aos defeitos da matriz Al2O3 e à banda LMCT do O→Eu3+, enquanto que as bandas finas são atribuídas às transições 7F0#&8594;5DJ, 5HJ e 5LJ oriundas do íon Eu3+. Os espectros de emissão dos sistemas Al2O3:Eu3+ (1%), obtidos pelos métodos de combustão, cerâmico e Pechini, e calcinados de 400 - 1100 ºC (λexc. = 394 nm) apresentam bandas alargadas atribuídas às transições 5D0→7FJ do íon Eu3+, sugerindo a ocupação de diferentes sítios de simetria neste sistema evidenciado através do alargamento inomogêneo das bandas atribuídas às transições 4f-4f do íon terra rara. A presença da inomogeneidade das transições eletrônicas 5D0→7FJ para Al2O3:Eu3+ (1%) calcinada de 400 a 1000 ºC sugere que este sistema apresenta predominância da fase gama (γ-Al2O3:Eu3+). A conversão da γ-Al2O3 (fase metaestável) em α-Al2O3 (fase estável - coríndon) promove alterações significativas nos espectros de emissão (λexc. = 394 nm). As amostras calcinadas de 1100 a 1400 ºC exibem um pico fino de alta intensidade (695 nm) atribuídas à linha R do íon Cr3+. A curva de decaimento luminescente do nível emissor 5D0 apresentou um comportamento bi-exponencial indicando que o íon Eu3+ encontra-se em um ambiente químico com diferentes sítios de simetria. O sistema Al2O3:Eu3+ preparado pelo método de combustão (400 - 1100 ºC) apresenta um aumento nos valores dos parâmetros de intensidades Ω2 com o aumento da temperatura de calcinação promovendo uma elevação do caráter covalente da interação metal-doador. Os valores da eficiência quântica de emissão (η) dos sistemas Al2O3:Eu3+ apresentam-se maiores comparados com outros sistemas vítreos. Observa-se que as coordenadas CIE dos compostos Al2O3:Eu3+ localizam-se próximas ao vértice correspondente à cor vermelha sugerindo uma grande contribuição desta cor. / In this work, Al2O3:TR3+ (TR3+=Eu, Gd) samples were prepared by ceramic, combustion and Pechini methods annealed at the temperature range of 400 - 1400 ºC. X-Ray diffraction -XRD patterns suggest that samples heated at lower temperatures are amorphous systems, but when the temperature increases, a change in the cubic phase of activated alumina (γ-Al2O3) is observed. The α-Al2O3 phase showed high crystallinity and thermostability annealed at 1200 ºC. Crystallite size was determined by Scherrer\'s method using XRDs. In general, infrared spectra of Al2O3:Eu3+ show stretching frequencies related to condensed and/or isolated tetrahedral groups [AlO4] indicating the presence of γ-alumina phase. It was observed the existence of bands in lower energies attributed to stretching frequencies of octahedral groups [AlO6] from α-alumina phase (corundum). The scanning electron microscopy (SEM) suggests that particles obtained by ceramic method show the smallest size and the most uniform morphology compared to those prepared by combustion and Pechini methods. Emission spectra (λ exc. = 320 nm) of AlAl2O3:Gd3+ system present no narrow bands arising from Cr3+ ions observed in the spectra of non-doped alumina indicating luminescence quenching by Gd3+ ion. Excitation spectra of Al2O3:Eu3+ samples prepared by three methods present a broad band attributed to defects of Al2O3 matrice and to LMCT state of O→Eu3+, on the other hand, the narrow bands are assigned to 7F0→5DJ, 5HJ and 5LJ transitions arising from Eu3+ ion. Emission spectra of Al2O3:Eu3+ (1%) system prepared by combustion, ceramic and Pechini methods, annealed from 400 to 1100 ºC (λexc. = 394 nm) show broad bands for 5D0→7FJ transitions of Eu3+ ion suggesting that this ion is in different symmetry sites indicated by inhomogeneous line broadening of bands attributed to 4f-4f transition from rare earth ion. The presence of inhomogeneity of 5D0→7FJ transitions for Al2O3:Eu3+ (1%) annealed from 400 to 1000 ºC suggests that this system presents predominantly the γ-alumina phase. The conversion of γ-Al2O3 (metastable phase) to α-Al2O3 (stable phase - corundum) changes significantly their emission spectra (λexc. = 394 nm). The samples annealed from 1100 to 1400 ºC, exhibited a high intensity narrow peak around 695 nm assigned to R lines of Cr3+ ion. Luminescence decay curves of 5D0 emitter level have a bi-exponential behavior indicating that Eu3+ ion is found in a chemical environment with different symmetry sites. The Al2O3:Eu3+ system prepared by combustion method at 400 -1100 ºC presents an increase in the Ω2 intensity parameter values with the increase of annealing temperatures enhancing the covalent character of metal-donator interaction. The values of emission quantum efficiencies (η) of Al2O3:Eu3+ are higher than those for vitreous systems. CIE coordinates of Al2O3:Eu3+ are located near the corner corresponding to monochromatic red color.

Neste trabalho, investigamos a influência da estrutura de energia das minibandas dos estados eletrônicos ocupados no tempo de recombinação em poços quânticos múltiplos (MQW) fracamente acoplados de GaAs / AlGaAs. Um dos melhores métodos para estudar o efeito da estrutura energética consiste em medir o tempo de recombinação eletrônica em função de parâmetros expostas à influência externa que afeta a estrutura energética, por isso, aplicamos um campo magnético externo. O espectro da emissão de fotoluminescência foi composta pelas contribuições das minibandas da banda de condução, Γ – Γ e Γ – XZ. Observou-se um aumento notável do tempo de recombinação quando o campo magnético causou a despopulação da minibanda de maior energia, Γ – XZ. O efeito observado é atribuído à variação induzida pelo campo magnético na densidade dos estados eletrônicos. / In the present work, we investigate the influence of the miniband energy structure of the populated electron states on the recombination time in GaAs/AlGaAs weakly coupled multiple quantum wells (MQW). The best method to study the effect of the energy structure is to measure the recombination time in the same sample subject to external influence which affects the energy structure, therefore, we apply an external magnetic field. The photoluminescence emission was composed of the contributions from the Γ – Γ and Γ – XZ conduction band minibands. Remarkable enhancement of the recombination time was observed when the magnetic field caused depopulation of the higher energy Γ – XZ miniband. The observed effect is attributed to the magnetic field induced variation of the electron density of states.

High performance optoelectronic applications require simultaneously high mobility ($\mu$) and high quantum efficiency of fluorescence ($\Phi$). While this has been realised for organic small molecule semiconductors, applications such as high efficiency organic photovoltaics and bright organic light-emitting diodes towards electrically driven lasing are hampered by an apparent trade-off between $\mu$ and $\Phi$ in disordered systems. Recent reports of state-of-the-art device performance often optimise $\mu$ and $\Phi$ in disordered organic materials separately, and employ multi-layer architectures. In this work, we investigate materials in a class of donor-acceptor polymer materials; the indacenodithiophene-$\textit{alt}$-benzothiadiazole family, which demonstrate high $\mu$ in spite of a low long-range structural order, to understand the interplay between these two important device figures-of-merit. In the first section, we evaluate the effect of various tuneable parameters on $\mu$ and device performance in organic field-effect transistors. Using chemical modifications to the solubilising side chains, we observe that the substitution of bulky groups leads to a reduction of the hole mobility $\mu_h$ > 2 cm$^{2}$/Vs to ~ 0.5 cm$^{2}$/Vs in the benchmark polymer of this family, indacenodithiophene-$\textit{alt}$-benzothiadiazole. Crystallographic and exciton-quenching based experiments confirm this observation is closely related to the degree of polymer backbone aggregation, and this leads to a different temperature evolution of the transport behaviour. In order to reliably improve $\mu$ in these systems, an elongation of the donor subunit is required. This increases the $\pi$-electron density on the donor, and can lead to an improvement in $\mu$ where the side chain density is decreasing. This chemical design, leading to a more highly aggregated structural motif is much more potent in determining $\mu$, it seems, than design strategies to further improve the energetic disorder in the joint density of states and the potential barrier to torsion, which may be near optimised in these low-disorder systems. In the second section, we unpick the precise relationship between the degree of aggregation apparently linking high $\mu$ to low $\Phi$. With a prototype system, we compare the photophysics of two indacenodithiophene-$\textit{alt}$-benzothiadiazole polymers differing by side chain bulkiness. Despite the aforementioned suppression of $\mu$, we observe an improvement to $\Phi$ of $< 0.02$ to $\sim 0.18$ upon backbone separation. This derivative has the highest $\Phi$ reported for any polymer with $\mu$ exceeding that of amorphous-Si. However, the $\Phi$ in the more aggregated derivative is not limited by the formation of non-emissive excitons, but rather by an additional internal conversion pathway which is strongly temperature dependent, and mediated by Raman-active vibrations and close chain coupling. Extending this study, we analyse additional materials in this family with the highest $\Phi \cdot \mu$ values reported for conjugated polymers. We find that increasing the energy gap leads to an increase in $\Phi$, and secondary emission pathways via weakly luminescent inter-chain charge transfer species. By solving the rate equations for exciton recombination, we use the radiative rate of inter-chain luminescence as a probe to show strong wavefunction mixing at close-contact points for some polymers, and suggest this as the origin for a superior $\mu$ in dithiopheneindenofluorene-$\textit{alt}$-benzothiadiazole compared to indacenodithiophene-$\textit{alt}$-benzothiadiazole. We demonstrate how low $\mu$ can be decoupled from the energy gap ($E_g$), and propose backbone elongation leading to increased inter-chain wavefunction overlap and a higher $E_g$ as a design rule to increase $\Phi$ and $\mu$ together. Finally, we assess the role of low-frequency vibrations in organic semiconductors displaying thermally activated delayed fluorescence (TADF). In the low-aggregation limit where $\Phi$ is maximised, we show that non-radiative triplet recombination is strongly related to low frequency torsional motion, and both are reduced in the presence of a rigid polymer host matrix for various TADF materials across different classes. However, we also explore the importance of rotational freedom in determining the oscillator strength, exchange energy, and spin-orbit coupling matrix elements which mediate luminescence in the absence of a rigid host. We demonstrate that suppressing dynamic motion is a powerful tool to modulate the photophysical properties of these emitters, and can lead to improved $\Phi$ particularly for low $E_g$ emitters.

Neste trabalho foram preparadas as amostras Al2O3:TR3+ (TR3+=Eu, Gd) pelos métodos cerâmico, combustão e Pechini, calcinadas de 400 - 1400 ºC. Os difratogramas de raios X sugerem que as amostras calcinadas em menores temperaturas apresentam-se como sistemas amorfos, que com a elevação da temperatura de calcinação transformam-se na fase cúbica das aluminas ativadas (&#947;-Al2O3). A partir de 1200 ºC forma-se a fase hexagonal de &#945;-Al2O3, altamente cristalina e termoestável. O tamanho dos cristalitos foi determinado pelo método de Scherrer a partir dos respectivos difratogramas. Em geral, os espectros no infravermelho de Al2O3:Eu3+ apresentaram estiramentos relativos aos grupos tetraédricos [AlO4] condensados e/ou isolados indicando a presença de fase &#947;-alumina. Foi também observada a existência de bandas em regiões de menores energias atribuídas às freqüências de estiramento de grupos octaédricos [AlO6] relativas à fase &#945;-alumina (coríndon). A Microscopia Eletrônica de Varredura (MEV) indicou que as partículas obtidas pelo método cerâmico apresentam menor tamanho e uma morfologia mais uniforme comparados com aquelas obtidas pelos métodos de combustão e Pechini. Os espectros de emissão (&#955; exc. = 320 nm) do sistema Al2O3:Gd3+ não apresentam as bandas finas oriundas dos íons Cr3+ observadas nos espectros da alumina não dopada, indicando que íon Gd3+ suprime a luminescência destes íons. Os espectros de excitação das amostras Al2O3:Eu3+ preparadas pelo três métodos apresentam uma banda larga atribuída aos defeitos da matriz Al2O3 e à banda LMCT do O&#8594;Eu3+, enquanto que as bandas finas são atribuídas às transições 7F0#&8594;5DJ, 5HJ e 5LJ oriundas do íon Eu3+. Os espectros de emissão dos sistemas Al2O3:Eu3+ (1%), obtidos pelos métodos de combustão, cerâmico e Pechini, e calcinados de 400 - 1100 ºC (&#955;exc. = 394 nm) apresentam bandas alargadas atribuídas às transições 5D0&#8594;7FJ do íon Eu3+, sugerindo a ocupação de diferentes sítios de simetria neste sistema evidenciado através do alargamento inomogêneo das bandas atribuídas às transições 4f-4f do íon terra rara. A presença da inomogeneidade das transições eletrônicas 5D0&#8594;7FJ para Al2O3:Eu3+ (1%) calcinada de 400 a 1000 ºC sugere que este sistema apresenta predominância da fase gama (&#947;-Al2O3:Eu3+). A conversão da &#947;-Al2O3 (fase metaestável) em &#945;-Al2O3 (fase estável - coríndon) promove alterações significativas nos espectros de emissão (&#955;exc. = 394 nm). As amostras calcinadas de 1100 a 1400 ºC exibem um pico fino de alta intensidade (695 nm) atribuídas à linha R do íon Cr3+. A curva de decaimento luminescente do nível emissor 5D0 apresentou um comportamento bi-exponencial indicando que o íon Eu3+ encontra-se em um ambiente químico com diferentes sítios de simetria. O sistema Al2O3:Eu3+ preparado pelo método de combustão (400 - 1100 ºC) apresenta um aumento nos valores dos parâmetros de intensidades &#937;2 com o aumento da temperatura de calcinação promovendo uma elevação do caráter covalente da interação metal-doador. Os valores da eficiência quântica de emissão (&#951;) dos sistemas Al2O3:Eu3+ apresentam-se maiores comparados com outros sistemas vítreos. Observa-se que as coordenadas CIE dos compostos Al2O3:Eu3+ localizam-se próximas ao vértice correspondente à cor vermelha sugerindo uma grande contribuição desta cor. / In this work, Al2O3:TR3+ (TR3+=Eu, Gd) samples were prepared by ceramic, combustion and Pechini methods annealed at the temperature range of 400 - 1400 ºC. X-Ray diffraction -XRD patterns suggest that samples heated at lower temperatures are amorphous systems, but when the temperature increases, a change in the cubic phase of activated alumina (&#947;-Al2O3) is observed. The &#945;-Al2O3 phase showed high crystallinity and thermostability annealed at 1200 ºC. Crystallite size was determined by Scherrer\'s method using XRDs. In general, infrared spectra of Al2O3:Eu3+ show stretching frequencies related to condensed and/or isolated tetrahedral groups [AlO4] indicating the presence of &#947;-alumina phase. It was observed the existence of bands in lower energies attributed to stretching frequencies of octahedral groups [AlO6] from &#945;-alumina phase (corundum). The scanning electron microscopy (SEM) suggests that particles obtained by ceramic method show the smallest size and the most uniform morphology compared to those prepared by combustion and Pechini methods. Emission spectra (&#955; exc. = 320 nm) of AlAl2O3:Gd3+ system present no narrow bands arising from Cr3+ ions observed in the spectra of non-doped alumina indicating luminescence quenching by Gd3+ ion. Excitation spectra of Al2O3:Eu3+ samples prepared by three methods present a broad band attributed to defects of Al2O3 matrice and to LMCT state of O&#8594;Eu3+, on the other hand, the narrow bands are assigned to 7F0&#8594;5DJ, 5HJ and 5LJ transitions arising from Eu3+ ion. Emission spectra of Al2O3:Eu3+ (1%) system prepared by combustion, ceramic and Pechini methods, annealed from 400 to 1100 ºC (&#955;exc. = 394 nm) show broad bands for 5D0&#8594;7FJ transitions of Eu3+ ion suggesting that this ion is in different symmetry sites indicated by inhomogeneous line broadening of bands attributed to 4f-4f transition from rare earth ion. The presence of inhomogeneity of 5D0&#8594;7FJ transitions for Al2O3:Eu3+ (1%) annealed from 400 to 1000 ºC suggests that this system presents predominantly the &#947;-alumina phase. The conversion of &#947;-Al2O3 (metastable phase) to &#945;-Al2O3 (stable phase - corundum) changes significantly their emission spectra (&#955;exc. = 394 nm). The samples annealed from 1100 to 1400 ºC, exhibited a high intensity narrow peak around 695 nm assigned to R lines of Cr3+ ion. Luminescence decay curves of 5D0 emitter level have a bi-exponential behavior indicating that Eu3+ ion is found in a chemical environment with different symmetry sites. The Al2O3:Eu3+ system prepared by combustion method at 400 -1100 ºC presents an increase in the &#937;2 intensity parameter values with the increase of annealing temperatures enhancing the covalent character of metal-donator interaction. The values of emission quantum efficiencies (&#951;) of Al2O3:Eu3+ are higher than those for vitreous systems. CIE coordinates of Al2O3:Eu3+ are located near the corner corresponding to monochromatic red color.