Correlated electron-hole plasma in organometal perovskites

Organic-inorganic perovskites are a class of solution-processed semiconductors holding promise for the realization of low-cost efficient solar cells and on-chip lasers. Despite the recent attention they have attracted, fundamental aspects of the photophysics underlying device operation still remain elusive. Here we use photoluminescence and transmission spectroscopy to show that photoexcitations give rise to a conducting plasma of unbound but Coulomb-correlated electron-hole pairs at all excitations of interest for light-energy conversion and stimulated optical amplification. The conductive nature of the photoexcited plasma has crucial consequences for perovskite-based devices: in solar cells, it ensures efficient charge separation and ambipolar transport while, concerning lasing, it provides a low threshold for light amplification and justifies a favourable outlook for the demonstration of an electrically driven laser. We find a significant trap density, whose cross-section for carrier capture is however low, yielding a minor impact on device performance

Light-Induced Charged and Trap States in Colloidal Nanocrystals Detected by Variable Pulse Rate Photoluminescence Spectroscopy

<p>Intensity instabilities are a common trademark of the photoluminescence of nanoemitters. This general behavior is commonly attributed to random fluctuations of free charges and activation of charge traps reducing the emission yield intermittently. However, the actual physical origin of this phenomenon is actively debated. Here we devise an experiment, variable pulse rate photoluminescence, to control the accumulation of charges and the activation of charge traps. The dynamics of these states is studied, with pulse repetition frequencies from the single-pulse to the megahertz regime, by monitoring photoluminescence spectrograms with picosecond temporal resolution. We find that both photocharging and charge trapping contribute to photoluminescence quenching, and both processes can be reversibly induced by light. Our spectroscopic technique demonstrates that charge accumulation and trap formation are strongly sensitive to the environment, showing different dynamics when nanocrystals are dispersed in solution or deposited as a film.</p>

Final FLaReNet deliverable: Language Resources for the Future - The Future of Language Resources

Language Technologies (LT), together with their backbone, Language Resources (LR), provide an essential support to the challenge of Multilingualism and ICT of the future. The main task of language technologies is to bridge language barriers and to help creating a new environment where information flows smoothly across frontiers and languages, no matter the country, and the language, of origin. To achieve this goal, all players involved need to act as a community able to join forces on a set of shared priorities. However, until now the field of Language Resources and Technology has long suffered from an excess of individuality and fragmentation, with a lack of coherence concerning the priorities for the field, the direction to move, not to mention a common timeframe. The context encountered by the FLaReNet project was thus represented by an active field needing a coherence that can only be given by sharing common priorities and endeavours. FLaReNet has contributed to the creation of this coherence by gathering a wide community of experts and making them participate in the definition of an exhaustive set of recommendations

Colloidal synthesis and characterization of Bi2S3 nanoparticles for photovoltaic applications

Bismuth sulfide is a promising n-type semiconductor for solar energy conversion. We have explored the colloidal synthesis of Bi2S3 nanocrystals, with the aim of employing them in the fabrication of solution-processable solar cells and to replace toxic heavy metals chalcogenides like PbS or CdS, that are currently employed in such devices. We compare different methods to obtain Bi2S3 colloidal quantum dots, including the use of environmentally benign reactants, through organometallic synthesis. Different sizes and shapes were obtained according to the synthesis parameters and the growth process has been rationalized by comparing the predicted morphology with systematic physical-chemistry characterization of nanocrystals by X-ray diffraction, FT-IR spectroscopy, Transmission Electron Microscopy (TEM)

Capturing Coercions in Texts: a First Annotation Exercise

In this paper we report the first results of an annotation exercise of argument coercion phenomena performed on Italian texts. Our corpus consists of ca 4000 sentences from the PAROLE sottoinsieme corpus (Bindi et al. 2000) annotated with Selection and Coercion relations among verb-noun pairs formatted in XML according to the Generative Lexicon Mark-up Language (GLML) format (Pustejovsky et al., 2008). For the purposes of coercion annotation, we selected 26 Italian verbs that impose semantic typing on their arguments in either Subject, Direct Object or Complement position. Every sentence of the corpus contains information about corpus-derived typed selectional preferences for verbs in the targeted argument slots and is annotated with the source type for the noun arguments by two annotators plus a judge. An overall agreement of 0.87 kappa indicates that the annotation methodology is reliable. A qualitative analysis of the results allows us to outline some suggestions for improvement of the task: 1) a different account of inherently polysemous nouns has to be devised and 2) a more comprehensive account of coercion mechanisms requires annotation of the deeper meaning dimensions that are targeted in coercion operations, such as those captured by Qualia relations

Domain-Specific Languages for Epigraphy: The Case of ItAnt

ItAnt is a research project devoted to the languages and cultures of ancient Italy witnessed by a digital collection of inscriptions. This contribution illustrates how the definition of a Domain-Specific Language can support the activity of the epigraphists involved in the project by increasing the human readability of the encoded data without sacrificing the compliance to standard models and formats. Finally, an example of concrete use of the encoded texts within the CLARIN-IT DigItAnt platform will be briefly described

Evaluating ImagAct-WordNet mapping for English and Italian through videos

In this paper we present the results of the evaluation of an automatic mapping between two lexical resources, WordNet/ItalWordNet and ImagAct, a conceptual ontology of action types instantiated by video scenes. Results are compared with those obtained from a previous experiment performed only on Italian data. Differences between the two evaluation strategies, as well as between the quality of the mappings for the two languages considered in this paper, are iscussed

Deliverable D.2.3 Loading Software: Final Version BioLexicon Data Base: Architecture and Application

BioLexicon Data Base: Architecture and Applicatio

SemEval-2010 Task 7: Argument Selection and Coercion

We describe the Argument Selection and Coercion task for the SemEval-2010 evaluation exercise. This task involves characterizing the type of compositional operation that exists between a predicate and the arguments it selects. Specifically, the goal is to identify whether the type that a verb selects is satisfied directly by the argument, or whether the argument must change type to satisfy the verb typing. We discuss the problem in detail, describe the data preparation for the task, and analyze the results of the submissions