Preface

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Optical properties of LiNbO3 : Cr crystals co-doped with Germanium oxide

Lithium niobate (LiNbO3) crystals doped with chromium ions show a clear green colouring reflecting the absorption profile of the dominating [Cr](Li) defect centres. A significant change in its colouration takes place when it is co-doped with other valency impurities such as Mg2+, Sc3+ and W6+, above a certain threshold concentration. This concentration singularity has been attributed to the formation of [Cr](Nb) centres coexisting with the [Cr](Li) centres. In this work, we extended the investigation on the effect of co-dopant ions in Cr:LiNbO3 to tetravalent cation such as GeO2. A singularity in the relative intensity of the (4)A(2)-> T-4(1) and (4)A(2)-> T-4(2) absorption band was observed for a concentration of similar to 1.5 mol%, compared with 4.5 mol% for Mg2+. The photoluminescence emission spectra also reveal a new emission band, at a lower energy than the [Cr](Li) centre, corresponding to this threshold concentration. A charge compensation model is proposed to explain the role of cation impurities and results are compared with those of other valence impurities

An interactive installation of African music and the Trans-Atlantic slave trade

This paper introduces Afrobits, an interactive installation about African music and the Trans-Atlantic slave trade. Its main aim is to bring to light invisible stories hidden behind geographic epistemologies. The installation highlights the contribution that African cultures had on the tangible and intangible cultural heritage of the world, such as popular music. Although it covers diverse countries, we focused on the Americas, placing emphasis on Latin-America as the biopolitical space that enabled the integration of native cultures with African peoples. As this project involved web scientists, graphic designers, historians, digital humanists and artists, we also discuss the benefits of interdisciplinary research; contributions from University researchers for the development of storytelling projects for the Cultural Heritage sector; and the implementation of complex technologies and research methods