Scientific Papers in SCI

The Palaces in the Alcazar of Seville, Spain, are famous for their ceramic decoration. The technique of tessellation was used extensively in all rooms in the Mudejar Palace, dated in the fourteenth century. These glazed ceramics have been analysed in situ using noninvasive quantitative chemical methods of X-ray fluorescence and diffraction (XRF and XRD). Micro-samples were taken to prepare cross-sections and analysed by optical and electronic microscopy. The composition of these ceramics, their manufacturing technique and the time of application in the different areas of the Palace have been characterized in this work. Five colours have been found in the glazed ceramics: green, black, molasses, white and blue. Fe, Co, Cu, Mn and Sn are the main chemical elements responsible for the colour of the glass phase of these ceramics. Wollastonite, quartz, bustamite and feldspars inclusions have been found in the glass phase. Casiterite and Malayaite have been also characterized by XRD. The ceramic paste used for manufacturing was calcic and was heated at about 900 degrees C. Thenardite, gypsum, sodium chloride and nitrogen compounds have been characterized in the ceramic and are responsible for their alteration. The information obtained in the 24 zones studied shows that there is no homogeneity in the ceramics due to the different times in which the tiles were placed and the restorations carried out over time. There are 3 main groups of ceramics: a) probably from 14th century, b), probably from 15-16th centuries and c) from 19-20th centuries and recent restorations. 

Fluoride-based compounds doped with rare-earth cations are the preferred choice of materials to achieve efficient upconversion, of interest for a plethora of applications ranging from bioimaging to energy harvesting. Herein, we demonstrate a simple route to fabricate bright upconverting films that are transparent, self-standing, flexible, and emit different colors. Starting from the solvothermal synthesis of uniform and colloidally stable yttrium fluoride nanoparticles doped with Yb3+ and Er3+, Ho3+, or Tm3+, we find the experimental conditions to process the nanophosphors as optical quality films of controlled thickness between few hundreds of nanometers and several micrometers. A thorough analysis of both structural and photophysical properties of films annealed at different temperatures reveals a tradeoff between the oxidation of the matrix, which transitions through an oxyfluoride crystal phase, and the efficiency of the upconversion photoluminescence process. It represents a significant step forward in the understanding of the fundamental properties of upconverting materials and can be leveraged for the optimization of upconversion systems in general. We prove bright multicolor upconversion photoluminescence in oxyfluoride-based phosphor transparent films upon excitation with a 980 nm laser for both rigid and flexible versions of the layers, being possible to use the latter to coat surfaces of arbitrary shape. Our results pave the way toward the development of upconverting coatings that can be conveniently integrated in applications that demand a large degree of versatility.