Analysis and optimization of light outcoupling in OLEDs with external hierarchical textures

Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.Fil: Kovacic, Milan. University of Ljubljana; EsloveniaFil: Samigullina, Dinara. University of Ljubljana; EsloveniaFil: Bouchard, Felix. Technische Universität Dresden; AlemaniaFil: Krc, Janez. University of Ljubljana; EsloveniaFil: Lipovšek, Benjamin. Technische Universität Dresden; AlemaniaFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Lasagni, Andres Fabian. Technische Universität Dresden; AlemaniaFil: Reineke, Sebastian. University of Ljubljana; EsloveniaFil: Topic, Marko. University of Ljubljana; Esloveni

Leptogenesis within a generalized quark-lepton symmetry

Quark-lepton symmetry has been shown to be inconsistent with baryogenesis via leptogenesis in natural schemes of the see-saw mechanism. Within the phenomenological approach of textures, we relax this strict symmetry and propose weaker conditions, namely models of the neutrino Dirac mass matrix $M_D$ which have the same hierarchy as the matrix elements of $M_u$. We call this guide-line generalized $hierarchical$ quark-lepton symmetry. We consider in detail particular cases in which the moduli of the matrix elements of $M_D$ are equal to those of $M_u$. Within the phenomenological approach of textures, we try for the heavy Majorana mass matrix diagonal and off-diagonal forms. We find that an ansatz for $M_D$ preserving the hierarchy, together with an off-diagonal model for the heavy Majorana neutrino mass, is consistent with neutrino masses, neutrino mixing and baryogenesis via leptogenesis for an intermediate mass scale $m_R \sim 10^{12}$ GeV. The preservation of the hierarchical structure could come from a possible symmetry scheme.Comment: 12 pages, RevTex4. Title and abstract changed. Revised and enlarged versio

Compatibility of A4A_{4} Flavour Symmetric Minimal Extended Seesaw with (3+1)(3+1) Neutrino Data

Motivated by the recent resurrection of the evidence for an eV scale sterile neutrino from the MiniBooNE experiment, we revisit one of the most minimal seesaw model known as the minimal extended seesaw that gives rise to a $3+1$ light neutrino mass matrix. We consider the presence of $A_4$ flavour symmetry which plays a non-trivial role in generating the structure of the neutrino mass matrix. Considering a diagonal charged lepton mass matrix and generic vacuum alignments of $A_4$ triplet flavons, we classify the resulting mass matrices based on their textures. Keeping aside the disallowed texture zeros based on earlier studies of $3+1$ neutrino textures, we categorise the remaining ones based on texture zeros, $\mu-\tau$ symmetry in the $3\times3$ block and hybrid textures. After pointing out the origin of such $3+1$ neutrino textures to $A_4$ vacuum alignments, we use the latest $3+1$ neutrino oscillation data and numerically analyse the texture zeros and $\mu-\tau$ symmetric cases. We find that a few of them are allowed from each category predicting interesting correlations between neutrino parameters. We also find that all of these allowed cases prefer normal hierarchical pattern of light neutrino masses over inverted hierarchy.Comment: 46 pages, 8 figures, 21 table

Right-handed Majorana Neutrino Mass Matrices for Generating Bimaximal Mixings in Degenerate and Inverted Models of Neutrinos

An attempt is made to generate the bimaximal mixings of the three species of neutrinos from the textures of the right-handed Majorana neutrino mass matrices. We extend our earlier work in this paper for the generation of the nearly degenerate as well as the inverted hierarchical models of the left-handed Majorana neutrino mass matrices using the non-diagonal textures of the right-handed Majorana neutrino mass matrices and the diagonal form of the Dirac neutrino mass matrices, within the frame work of the seesaw mechanism in a model independent way. Such Majorana neutrino mass models are important to explain the recently reported result on the neutrinoless double beat decay (0/nu/beta/beta) experiment,together with the earlier established data on LMA MSW solar and atmospheric neutrino oscillations.Comment: 14 pages, To appear in IJMPA (2003

Classification and Application of Triangular Quark Mass Matrices

The hierarchical structure in the quark masses and mixings allows its ten physical parameters to be most conveniently encoded in mass matrices of the upper triangular form. We classify these matrices in the hierarchical, minimal parameter basis where the mismatch between the weak and mass eigenstates involves only small mixing angles. Ten such pairs are obtained for the up and down quarks. This analysis can be used to classify texture zeros of general mass matrices. For hermitian mass matrices with five texture zeros, this method yields immediately five pairs of textures with simple, analytic predictions for the quark mixings. Comparison with data indicates that, of the five pairs, three are disfavored, one is marginally acceptable, while the fifth fits well.Comment: 18 pages, ReVTe

A New Approach to Texture Analysis of Quark Mass Matrices

The triangular basis is proposed as an efficient way of analyzing general quark mass matrices. Applying the method to hermitian hierarchical matrices with five texture zeros, analytic predictions for quark mixing can be readily obtained. One unique texture pair is found most favorable with present data. Some remarks are also made concerning parallel textures between the up and down quark mass matrices with four zeros.Comment: 4 pages, talk presented at PASCOS'99, Lake Tahoe, California, December 10-16, 199