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We present a systematic study on the effect of surface ligands on the luminescence properties and colloidal stability of β-NaYF4:Yb3+,Er3+ upconversion nanoparticles (UCNPs), comparing nine different surface coatings to render these UCNPs water-dispersible and bioconjugatable. A prerequisite for this study was a large-scale synthetic method that yields ~2 g per batch of monodisperse oleate-capped UCNPs providing identical core particles. These ~23 nm sized UCNPs display an upconversion quantum yield of ~0.35% when dispersed in cyclohexane and excited with a power density of 150 W cm-2, underlining their high quality. A comparison of the colloidal stability and luminescence properties of these UCNPs, subsequently surface modified with ligand exchange or encapsulation protocols, revealed that the ratio of the green (545 nm) and red (658 nm) emission bands determined at a constant excitation power density clearly depends on the surface chemistry. Modifications relying on the deposition of additional (amphiphilic) layer coatings, where the initial oleate coating is retained, show reduced non-radiative quenching by water as compared to UCNPs that are rendered water-dispersible via ligand exchange. Moreover, we could demonstrate that the brightness of the upconversion luminescence of the UCNPs is strongly affected by the type of surface modification, i.e., ligand exchange or encapsulation, yet hardly by the chemical nature of the ligand.
Several glazed ceramic fragments (XVIth to XVIIIth centuries) from two production centers in Portugal (Coimbra and Lisbon) were the object of this study. The ones from Coimbra comprise two sets of samples: faiences and tiles. The ones from Lisbon are only tiles (azulejos, in Portuguese). The three main divisions of such pieces are the ceramic support (body), glaze and surface decoration. The system decoration/glaze is not easy to investigate, due to the high heterogeneity resulting from the mixing procedures and firing temperatures used. Moreover, the ability of the pigment to diffuse into the base glaze varies depending on the composition of both the pigment and the glaze in terms of fusibility. In order to raster these effects, high resolution techniques are required. In this work, synchrotron micro-X-ray fluorescence (µ-XRF) analysis was performed to monitor the profiles of the characteristic elements from the colors used and the glaze in well prepared cross-sections of the samples. Key elements are: Co for blue, Mn for purple, Cu for green, Sb for yellow, Pb for the glaze and Fe for the body. The major difference observed is that faiences have glaze thicknesses between 150 and 200 µm and tiles have glaze thicknesses between 350 and 400 µm. Furthermore, in faiences all the pigments except the yellow ones are well dispersed into the glassy matrix, while in tiles, all of them are just partially diffused throughout the glaze. However, differences between the tiles from Coimbra and Lisbon were observed. In the samples from Lisbon, a higher intake from the pigment throughout the glaze is observed.
Die Empfindlichkeit von Eindring- und Magnetpulverprüfungen (PT, MT) hängt unter anderem von der Eignung und der Qualität der Prüfmittel ab (für PT bezeichnet als Eindringsystem). Die Ermittlung der Empfindlichkeit erfolgt an Kontrollkörpern mit natürlichen und künstlichen Inhomogenitäten durch Ermittlung der Anzeigenerkennbarkeit als Maß für die Eignung. Die europäischen Normen spezifizieren die Anforderungen an die Prüfmittel für Typen-, Chargen- und Betriebsprüfungen nach pr EN ISO 3452-2 für PT und EN ISO 9934-2 für MT. Dieser Beitrag beschreibt die Ermittlung der Empfindlichkeit von Prüfmitteln sowie deren Qualifizierung bei der Typenprüfung. Die vorgeschlagenen Verfahren wurden durch experimentelle Untersuchungen validiert, bei denen ein Bildverarbeitungssystem zur Ermittlung der Anzeigenerkennbarkeit verwendet wurde. Im Hinblick auf die Qualifizierung der Prüfmittel wird die Zuverlässigkeit der Verfahren diskutiert.