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Developing Large grain Perovskites Over Large Areas and Investigating Degradation Using ElectroluminescenceAlmutawah, Zahrah Sadiq 11 July 2022 (has links)
No description available.
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Fabrication and characterization of nanodevices based on III-V nanowiresDe luna bugallo, Andres 06 July 2012 (has links) (PDF)
Semiconductor nanowires are nanostructures with lengths up to few microns and small cross sections (10ths of nanometers). In the recent years the development in the field of III-N nanowire technology has been spectacular. In particular they are consider as promising building in nanoscale electronics and optoelectronics devices; such as photodetectors, transistors, biosensors, light source, solar cells, etc. In this work, we present fabrication and the characterization of photodetector and light emitter based devices on III-N nanowires. First we present a study of a visible blind photodetector based on p-i-n GaN nanowires ensembles grown on Si (111). We show that these devices exhibit a high responsivity exceeding that of thin film counterparts. We also demonstrate UV photodetectors based on single nanowires containing GaN/AlN multi-axial quantum discs in the intrinsic region of the nanowires. Photoluminescence and cathodoluminescence spectroscopy show spectral contributions above and below the GaN bandgap according to the variation of the discs thickness. The photocurrent spectra show a sub-band-gap peak related to the interband absorption between the confined states in the large Qdiscs. Finally we present a study of photodetectors and light emitters based on radial InGaN/GaN MQW embedded in GaN wires. The wires used as photodetectors showed a contribution below the GaN bandgap. OBIC measurements demonstrate that, this signal is exclusively generated in the InGaN MQW region. We showed that LEDs based on this structure show a electroluminescence emission and a red shift when the In content present in the QWs increases which is in good agreement with photoluminescence and cathodoluminescence results.
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[en] PRODUCTION AND CHARACTERIZATION OF ORGANIC ELECTROLUMINESCENT DEVICES (OLEDS) BASED ON (BETA)-DICEKETONE RARE-EARTH COMPLEXES / [pt] PRODUÇÃO E CARACTERIZAÇÃO DE DISPOSITIVOS ORGÂNICOS ELETROLUMINESCENTES (OLEDS) BASEADOS EM COMPLEXOS (BETA)-DICETONATOS DE TERRAS-RARASWELBER GIANINI QUIRINO 27 September 2007 (has links)
[pt] Este trabalho apresenta os resultados de um estudo que envolve a
fabricação e a caracterização de dispositivos orgânicos emissores de luz
(OLEDs) baseados em complexos β-dicetonatos de terras-raras. O estudo se
coloca como continuação lógica da linha de pesquisa em dispositivos
eletroluminescentes baseados em íons terras-raras, começada alguns anos
atrás neste grupo de pesquisa. Para a produção dos dispositivos foram
empregadas várias técnicas de deposição de filmes finos, tais como deposição
térmica resistiva, pulverização catódica assistida por plasma (rf-magnetronsputtering)
e spin-coating. A síntese dos compostos orgânicos, bem como alguns
estudos adicionais puderam ser realizadas através de colaborações com
diversos grupos de pesquisas nacionais, os quais dispõem de recursos e
capacitação em áreas complementares. Os complexos orgânicos estudados
foram divididos em três conjuntos, que chamamos de sistemas. No sistema 1,
estudou-se o complexo Eu(bmdm)3(ttpo)2, onde o ligante orgânico bmdm é um
conhecido agente absorvedor de radiação UV bastante usado em protetores
solares. Os OLEDs baseados neste complexo apresentaram intensa foto- e
eletroluminescência com alta pureza de cor dada apenas pelas finas transições
características do íon Eu3+. No sistema 2, estudou-se o complexo chamado de
binuclear. Este composto tem dois núcleos terras-raras coordenados numa
mesma molécula. O primeiro binuclear estudado, o complexo
Eu(btfa)3 phenterpy Tb(acac)3, não apresentou as transições características dos
íons Tb3+ e Eu3+ como era esperado inicialmente. Por outro lado, apresentou
uma eletroluminescência sintonizável em duas situações distintas, a primeira em
função da tensão aplicada e a segunda através de mudanças na arquitetura das
camadas constituintes. Por causa desse efeito, mostramos a possibilidade de se
construir um dispositivo OLED emissor de luz branca. Ainda nesse sistema,
foram estudados OLEDs com complexos modificados quimicamente, chamados
de binuclear 2 e trinuclear. O complexo binuclear 2 apresentou as linhas de
emissão dos íons Tb3+ e Eu3+. Apesar de menos eficiente que o primeiro
complexo binuclear, este estudo mostrou que através de manipulações
moleculares (nanotecnologia) é possível sintetizar compostos capazes de emitir
as linhas características de emissão dos íons terras-raras, ou seja, com um
único complexo é possível obter duas emissões distintas. Por último, ainda como
sistema 2, o complexo trinuclear, é uma mistura de compostos orgânicos
contendo Tm, Tb e Eu e não formam uma única molécula, como no caso dos
compostos binucleares. Este estudo foi iniciado recentemente e ainda não foi
completamente explorado. Os primeiros testes mostraram que é possível usar
este complexo também para fabricar OLEDs com emissão de cor branca,
variando-se as quantidades relativas de Tm, Tb e Eu da mistura. Sabendo-se
que os ligantes β-dicetonas são os responsáveis pela transferência de energia
para os íons TR3+, através do efeito antena, o sistema 3, despontou como
grande novidade, mostrando a construção de dispositivos eletroluminescentes
baseados em complexos tetrakis(β-dicetonatos) de TR, ou seja, compostos que
possuem quatro ligantes β-dicetonas coordenandos a um único íon TR. Com
esse sistema conseguimos pela primeira vez uma emissão eficiente e pura das
principais transições do íon Tb à temperatura ambiente. O trabalho apontou,
também, que tanto a irradiação com luz UV, quanto a exposição aos agentes
atmosféricos (oxigênio, água, umidade, etc.) contribuem para uma rápida
degradação dos complexos orgânicos com conseqüente decaimento do
desempenho dos dispositivos fabricados. Para tanto, iniciamos um estudo para
investigar as causas da degradação de alguns dos compostos orgânicos
utilizados na fabricação de OLEDs. Os estudos de fotoabsorção e fotoemissão
realizados no Laboratório Nacional de Luz Síncrotron foram fundamentais para
uma maior compreensão destes efeitos. Os resultados deste estudo mostraram
que as técnicas espectroscópicas empregadas neste trabalho podem ser
utilizadas para se investigar a estrutura eletrônica, bem como a fotodegradação
de compostos orgânicos usados na fabricação de OLEDs. Utilizando a
espectroscopia de fluorescência, se estudou a viabilidade de se construir um
dosímetro de radiação ultravioleta portátil e de uso pessoal usando um OLED
cuja eletroluminescência é sensível à radiação UV. / [en] In this work we present the results of a study that
involves the manufacture
and the characterization of organic eletroluminescent
devices (OLEDs) based on
(beta)-diketonates Rare-Earth complexes. The investigation
reported is a continuation
of the research in electroluminescent devices based on
rare-earth ions, started
some years ago in our Group. For the production of the
devices were applied
several thin films deposition techniques: thermal
resistive, rf-magnetronsputtering
and spin-coating. The synthesis of organic compounds, as
well some
additional studies, were carried on through the
collaboration with different
brazilian research groups, which have resources and
qualification in
complementary areas. The organic compounds studied in this
thesis have been
divided in three groups, named systems. In system 1, the
studied complex was
Eu(bmdm)3(ttpo)2, where the organic bmdm ligand is a known
UV sensitive
material, frequently used in sunblockers. The OLEDs based
on this complex
presented intense photo- and electroluminescence with high
pure color emission
due to the almost atomic transitions characteristic of the
Eu3+ ion. In system 2, a
binuclear complex, represented by the molecular formula
Eu(btfa)3 phenterpy Tb(acac)3 was studied. This complex
has two rare-earth
nuclei coordinated in the same molecule. The OLEDs based
on this complex did
not present the Tb3+ and Eu3+ characteristic transitions
as expected. On the other
hand, the complex gave us the possibility to develop an
OLED with white color
emission. Probably the major novelty of this thesis is
represented by system 3.
Indeed, knowing that the (beta)-diketone ligands are the
main responsible for the RE3+
ions energy transference through the antenna effect, in
system 3, we investigated
the possibility to fabricate electroluminescent devices
based on RE (beta)-diketonate
tetrakis complexes, which have four coordinated (beta)-
diketones ligand to an RE ion
in order to enchance the energy transfer and the emission
efficiency. With this
system we obtained, for the first time, an efficient and
pure Tb emission at room
temperature.
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[en] PRODUCTION AND CHARACTERIZATION OF ORGANIC LIGHT EMITTING DEVICES (OLEDS) BASED ON SUPRAMOLECULAR COMPLEXES / [pt] PRODUÇÃO E CARACTERIZAÇÃO DE DISPOSITIVOS ORGÂNICOS ELETROLUMINESCENTES (OLEDS) BASEADOS EM COMPLEXOS SUPRAMOLECULARESCRISTIANO LEGNANI 06 December 2006 (has links)
[pt] Neste trabalho são apresentados os resultados da produção
e
caracterização de novos dispositivos orgânicos
eletroluminescentes
(OLEDs), que podem ser divididos idealmente em três
grupos. O primeiro
composto pelos OLEDs que utilizam os distirilbenzenos
(DSBs) como
camada eletroluminescente. Os DSBs são sistemas
utilizados
em química
supramolecular como pontes para transferência de carga.
No
segundo
colocamos os OLEDs baseados em 2; 6 - bis(dietanolamina) -
4; 8 -
dipiperidinopirimida (5; 4-d) pirimidina (DIP), que é uma
droga
amplamente conhecida e utilizada no tratamento de doenças
cardiovasculares, que por possuir uma intensa
fluorescência despertou a
curiosidade para investigarmos a possibilidade da sua
utilização com
camada eletroluminescente. A utilização do DIP como camada
eletroluminescente resultou em um OLED com a maior
luminância dos
grupos estudados, 1500 cd/m2. O terceiro grupo é formado
por OLEDs
que utilizam moléculas de calixarenos ([Al . 1]3+ e [Zn .
1]2+
onde 1 = 8-
oxiquinolinacalix[4]areno) como camada transportadora de
elétrons e
eletroluminescente. Foram estudados dois sistemas
calixarenos, o
primeiro sistema é coordenado com alumínio (calix[Al]3+)
e
o segundo
coordenado com zinco (calix[Zn]2+). O sistema calix[Al]3+
apresentou uma
interessante propriedade de cooperação entre o anel
central calix e um
grupamento quinolina coordenado com Al. Utilizando este
mecanismo de
sinergia produzimos um OLED sintonizável, o qual varia o
pico de sua
banda de eletroluminescência de 510 nm pra 470 nm em
função da
tensão aplicada. Desta forma a cor da luz emitida pelo
dispositivo pode
ser variada com continuidade do azul (X=0,26 : Y=0,33
coordenadas CIE)
até o verde claro (X=0,18 : Y=0,25).Todos os sistemas
orgânicos foram
analisados de um ponto de vista térmico através da
analise
de
calorimetria diferencial de varredura (DSC), com a qual
determinamos sua temperatura de transição vítrea (Tg).
Com
o auxilio de medidas
eletroquímicas, estabelecemos um procedimento
experimental
simples e
rápido para determinar os níveis energéticos HOMO
(highest
occupied
molecular orbital) dos materiais orgânicos estudados na
forma de filmes.
Enfim, através da caracterização elétrica foi possível
determinar o tipo de
injeção de portadores que governa os dispositivos bem
como
o modelo
que controla o transporte de cargas no interior dos OLEDs. / [en] In this work the results of the production and
characterization of new
organic electroluminescent devices (OLEDs) are presented
and
discussed. The work can be ideally divided in three parts.
The first is
composed by the OLEDs that use the distyrilbenzene (DSBs)
compounds
as electroluminescent layer. The DSBs are systems used in
supramolecular Chemistry as bridges for load transfer.
This is the first time
that they are used in small molecule OLEDs. The second
part deals with
OLEDs based on dipyridamole (2; 6-bis(diethanolamino) - 4;
8 -
dipiperidinopyrimido (5; 4-d)pyrimidine) (DIP) molecule,
which is a very
well known anti-platelet drug thoroughly used in the
treatment of hearth
diseases that for possessing an intense fluorescence woke
up our
curiosity in order to investigate the possibility of its
use as
electroluminescent layer. The use of DIP as
electroluminescent layer
resulted in a particular OLED with the highest luminance
of the
investigated devices, about 1500 cd/m2. Finally, the third
part involves
OLEDs that use calixarenes molecules [Al . 1]3+ and [Zn . 1]
2+
(1 = 8-
oxyquinolinecalix[4]arene) as electroluminescent and
electron transporting
layer. In this work were studied two calixarenes systems:
the first system
is coordinated with aluminum (calix[Al]3+) and the second
one is
coordinated with zinc (calix[Zn]2+). The first one
presented an interesting
cooperation property among the central calix ring and the
quinolina group
coordinated with the Al metal. Using this synergic
mechanism we were
able to produce a tunable OLED, which electroluminescent
emission
varies continuously from 510 nm to 446 nm as a function of
the applied
bias voltage. All the organic compounds used in this work
were analyzed
from a thermal point of view through a Differential
Scanning Calorimetry
(DSC), in order to determine their transition glass
temperature (Tg). By using electrochemistry measurements
it was possible to establish a
systematic and simple experimental procedure to determine
the HOMO
(highest occupied molecular orbital) energy levels of the
organic materials
studied in the form of films. Finally, through the
electrical characterization it
was possible to determine the type of carrier injection
that governs the
fabricated devices as well as the model that controls the
carrier transport
inside the OLEDs.
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Electro-optical Emission of Heterocyclic Aromatic Rigid-rod Polymers Containing Sulfonated PendantsHan, Shen-Rong 24 July 2004 (has links)
In this research, we investigated a novel rigid-rod polymer sPBI for mono-layer polymer light emitting diode (PLED) fabrication and luminescence emission. sPBI could be a luminescent polymer with a low threshold voltage of 4.5 V and green light electroluminescence emission (530 nm). Its SO3H pendant attached to the p-phenyl ring improved electronic delocalization along the backbone resulted in a red shift of the absorption spectrum. By attaching propanesulfonated pendants to the heterocyclic moiety of intractable fully conjugated sPBI, water-soluble rigid-rod polyelectrolyte sPBI-PS(Li+) was synthesized to promote its processibility in water or common organic solvent. This water-soluble rigid-rod polyelectrolyte sPBI-PS(Li+) was fabricated for polymer light-emitting electrochemical cells (PLECs) with LiCF3SO3 (LiTf) or LiN(CF3SO2)2 (LiTfSI) dopants for investigating the influence of propanesulfonated pendants as well as dopants on the opto-electronic emission and the room-temperature DC conductivity. The effect of lithium salts (LiTf or LiTfSI) on photoluminescence color of doped sPBI-PS(Li+) films was negligible. sPBI-PS(Li+) PLECs doped with 0.41 and 1.01 wt. % of LiTfSI showed higher green light electroluminescence emission (514 nm) with a lower threshold voltage of 3.0 V and -4.6 V, respectively. Emission brightness of the sPBI-PS(Li+) PLEC did not raise upon increasing the ionic conductivity of the luminescent layer.
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Light Emitting Diodes of Non-fully Conjugated Coil-like and Fully Conjugated Rigid-rod Heterocyclic Aromatic Homopolymers with Push-pull PendantsWen, Hong-ta 12 July 2008 (has links)
ABSTRACT
Light emitting diodes of non-fully conjugated coil-like homopolymers and fully conjugated rigid-rod homopolymers with electron withdrawing or donating group were studied. A series of Poly[2,2-(m-2-X-phenylene)-4-4¡A-hexafluoroisopropane- bibenzoxazoles] (6F-PBO-X, with X = amine, hydrogen and nitro) and poly-p-(2-X- phenylene)-benzobisoxazole (PBO-X, with X = amine, hydrogen and nitro) were synthesized for light emitting diode applications to observe electroluminescence emission affected by electron withdrawing or donating group.
All polymers were fabricated identically to form bi-layer light emitting diodes. In the devices, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonite)(PEDOT:PSS) was applied to be a hole transport layer; indium tin oxide (ITO) was the anode; and aluminum was the cathode.
Devices of the non-fully conjugated coli-like polymers (6F-PBO-X) and the fully conjugated rigid-rod polymers (PBO-X) all showed threshold voltage about 4 V. In the electroluminescence (EL) spectrum, the maximum intensity of non-fully conjugated polymer (6F-PBO-X) with amine (-NH2), hydrogen (-H) or nitro (-NO2) functional group was at 499 nm, 505 nm and 515 nm, respectively, showing a 20 nm wavelength shift. From ¡VNH2, -H and ¡VNO2 groups, their Commission International de l`Eclairage (C. I. E.) coordinates were (0.30, 0.46), (0.34, 0.45) and (0.40, 0.46), respectively. The EL maximum intensity for fully conjugated rigid-rod polymer PBO-X was at 521 nm (-NH2) and 474 nm (-NO2) showing a 50 nm wavelength shift. Their C. I. E. coordinates were (0.42, 0.45) and (0.25, 0.38), respectively. This is attributed to the fully conjugated, collinear, coplanar, rigid-rod polymers (PBO-X) backbone readily affected by the push-pull functional groups showing a large red shift.
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InAlGaAs/InP light emitting transistors and transistor lasers operating near 1.55 μmHuang, Yong 02 November 2010 (has links)
Light emitting transistors (LETs) and transistor lasers (TLs) are newly-emerging optoelectronic devices capable of emitting spontaneous or stimulated light while performing transistor actions. This dissertation describes the design, growth, and performances of long wavelength LETs and TLs based on InAlGaAs/InP material system. First, the doping behaviors of zinc (Zn) and carbon (C) in InAlGaAs layers for p-type doping were investigated. Using both dopants, the N-InP/p-In0.52(AlxGa1-x)0.48As/N-In0.52Al0.48As LETs with InGaAs quantum wells (QWs) in the base demonstrate both light emission and current gains (β). The device performances of Zn- and C-doped LETs have been compared, which is explained by a charge control analysis involving the quantum capture and recombination process in the QWs. A TL based on a C-doped double heterostructure (DH-TL) with single QW was designed and fabricated. The device lases at 77 K with a threshold current density (Jth) of 2.25 kA/cm2, emission wavelength (λ) at ~1.55 µm, and β of 0.02. The strong intervalence band absorption (IVBA) is considered as the main intrinsic optical loss that prohibits the device from lasing at room temperature. Based on a threshold condition analysis taking into account the strong IVBA, it is found that room-temperature lasing of a DH-TL is achieved only when the base thickness and doping level are within a specific narrow range and improved performance is expected in a separate confinement heterostructure (SCH) TL.
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Nanoskalige Halbleiter und funktionalisierte Kohlenstoffmaterialien: Darstellung, Charakterisierung und Anwendung in ElektrolumineszenzbauteilenSchrage, Christian 04 October 2010 (has links) (PDF)
In dieser Arbeit werden zwei Schwerpunkte behandelt. Zum Einen soll der Einsatz nanoskaliger Materialien als Funktionskomponenten in Elektrolumineszenzbauteilen beschrieben werden. Dabei wird in einem ersten Aufbau ein transparenter Nanokompositfilm als emittierende Schicht in einem, den organischen Leuchtdioden, analogen Aufbau eingesetzt, während in einer zweiten Struktur eine transparente Elektrode, die auf nanoskaligen Kohlenstoffmaterialien (Kohlenstoffnanoröhren bzw. Graphenen) basiert, hinsichtlich ihrer Eignung als Alternative zu etablierten transparenten Elektroden untersucht werden soll. In weiterführenden Arbeiten werden die Erfahrungen aus der Graphensynthese auf die Generierung poröser, funktionalisierter Kohlenstoffmaterialien angewendet. Verbindend, wird die Röntgenkleinwinkelstreuung eingesetzt, um in vergleichenden Untersuchungen möglichst detailierte Informationen über die jeweiligen Systeme zu erhalten.
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Transferts d'énergie dans des titanates dopés Pr 3+ et application au développement d'afficheurs électroluminescents par pulvérisation cathodiqueSarakha, Ludovic 03 February 2011 (has links) (PDF)
Ce travail de thèse est une contribution au développement d'afficheurs électroluminescents inorganiques utilisant le luminophore CaTiO3 :Pr3+ comme couche active. Il comporte deux volets. Le premier concerne l'étude du dépôt de CaTiO3 :Pr3+ par pulvérisation cathodique à partir d'une cible céramique élaborée au laboratoire et s'est plus particulièrement attaché à l'influence de la pression de dépôt et aux conditions de recuit (température, type de fours) sur les propriétés morphologiques, structurales, optiques et électriques des films. Les films obtenus sont cristallisés en structure orthorhombique, photoluminescents, transparents sur toute la gamme du visible et possèdent des propriétés électriques compatibles avec l'application visée. Des pistes d'optimisation de ces propriétés sont également avancées. Le second volet du travail utilise le modèle de transfert de charge par intervalence (TCIV) développé ces dernières années au laboratoire, pour orienter la recherche d'autres luminophores dopés par des ions Pr3+ utilisables dans des afficheurs électroluminescents. Sur cette base, des titanates de formulations (Ca,Sr)TiO3 :Pr3+, CaTiO3 :Bi3+ ;Pr3+ et Na1/2Ln1/2TiO3 :Pr3+ (Ln = La, Gd, Y, Lu) ont été synthétisés et caractérisés. L'évaluation détaillée du comportement de ces matériaux en photoluminescence a permis de valider le modèle TCIV, d'initier d'autres modèles et de mettre en évidence l'intérêt d'un codopage au bismuth pour accroître l'intensité de fluorescence de l'ion Pr3+ dans la matrice CaTiO3. Le luminophore rouge CaTiO3 :Bi3+ ; Pr3+ apparaît être un candidat intéressant pour des applications en électroluminescence.
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Silicon Nanocrystals Embedded In Sio2 For Light Emitting Diode (led) ApplicationsKulakci, Mustafa 01 September 2005 (has links) (PDF)
In this study, silicon nanocrystals (NC) were synthesized in silicon dioxide matrix by ion implantation followed by high temperature annealing. Annealing temperature and duration were varied to study their effect on the nanocrystal formation and optical properties. Implantation of silicon ions was performed with different energy and dose depending on the oxide thickness on the silicon substrate. Before device fabrication, photoluminescence (PL) measurement was performed for each sample. From PL measurement it was observed that, PL emission depends on nanocrystal size determined by the parameters of implantation and annealing process. The peak position of PL emission was found to shifts toward higher wavelength when the dose of implanted Si increased. Two PL emission bands were observed in most cases. PL emission around 800 nm originated from Si NC in oxide matrix. Other emissions can be attributed to the luminescent defects in oxide or oxide/NC interface.
In order to see electroluminescence properties Light Emitting Devices (LED) were fabricated by using metal oxide semiconductor structure, current-voltage (I-V) and electroluminescence (EL) measurements were conducted. I-V results revealed that, current passing through device depends on both implanted Si dose and annealing parameters. Current increases with increasing dose as one might expect due to the increased amount of defects in the matrix. The current however decreases with increasing annealing temperature and duration, which imply that, NC in oxide behave like a well controlled trap level for charge transport. From EL measurements, few differences were observed between EL and PL results. These differences can be attributed to the different excitation and emission mechanisms in PL and EL process. Upon comparision, EL emission was found to be inefficient due to the asymmetric charge injection from substrate and top contact. Peak position of EL emission was blue shifted with respect to PL one, and approached towards PL peak position as applied voltage increased. From the results of the EL measurements, EL emission mechanisms was attributed to tunneling of electron hole pairs from top contact and substrate to NC via oxide barrier.
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