Sustainable inorganic pigments with high near-infra-red reflectance based on Fe3+ doped YAlO3 for high temperature applications

Non-toxic inorganic pigments based on the Fe(III)-doped YAlO3 with high near-infra-red (NIR) reflectance were synthesized by a modified Pechini method at 1200 °C. A complete solid solution in the YAl1−xFexO3 system (0 ≤x ≤ 1) was prepared, yielding a wide range of colourations from yellow to red, depending on the iron content. Good pigment stability was achieved in a commercial high temperature glaze, used in the ceramic industry to colour glazes on tiles. The pieces coated with the pigmented glazes reached NIR solar reflectance values between 43% and 32%. The temperature protection studies carried out with the glazes pigmented with YAl0.75Fe0.25O3 and YFeO3 compositions, conclude that the pigmented samples reduce the temperature of a building by 5 °C and 4 °C, respectively, in comparison to the unpigmented glaze. Thus, these pigments can be excellent candidates for used in high-temperature applications such as colouring ceramic high temperatures glazes, as well as cool pigments in walls or roofs of buildings.Funding for open access charge: CRUE-Universitat Jaume

Practical guidance for easily interpreting the emission and physicochemical parameters of Eu3+ in solid-state hosts

Materials doped with the luminescent Eu3+ ion are attracting an ever-increasing amount of attention due to their potential applications in solid-state lighting, display devices, solar cells, or bioanalytics. But, why Eu3+? Unlike other lanthanides, its electronic features make the calculation of some physicochemical parameters quite straightforward, since they can be extracted directly from the emission spectrum. Highly appreciated for its reddish emission, the luminescent ion has also been widely used as a site-sensitive structural probe. With this in mind, this paper aims to offer easy guidance with helpful advice on how to interpret measurements of the emission spectra. It also presents the most useful tools for saving time, and gives a focused and practical explanation of the theoretical concepts involved.Funding for open access charge: CRUE-Universitat Jaume

The unexplored δ-phase of KY3F10: toward novel Eu3+-doped nanoplates with a ‘super-diamond’ structure for optical applications

This article describes a new, simple, and high-yield method based on a sonochemical process for obtaining the δ-KY3F10·xH2O compound with a ‘super-diamond’ structure, a material that has been completely neglected in the literature since it was first discovered. We explore the mechanism underlying the formation of the synthesized nanomaterials and show their connection with the pH of the medium. Additionally, we demonstrate for the first time the adequacy of the δ-phase of KY3F10 for optical applications through the novel Eu3+-doped nanoplates, which exhibit long lifetimes and high quantum efficiencies. The results reveal that this material, which also has zeolitic characteristics, can have a strong impact on future photonic and associated applications

Kinetics or thermodynamics? Extolling their role to modulate the crystal phases and luminescence of KY3F10:Eu3+ powders

KY3F10, a fluoride compound with two polymorphs (alpha and delta), has been a subject of study due to its unique properties. Obtaining the metastable delta-phase has been challenging, but this study presents an enhanced synthetic methodology using coprecipitation to isolate specific crystal phases. Varying the reaction temperature and time allows for the modulation of polymorph formation. The structural analysis of the synthesized powders reveals the influence of kinetic and thermodynamic control. The morphology of the particles is also affected by these factors, with different reaction conditions leading to distinct particle shapes. The luminescent response of Eu3+-doped powders helps understand the structural stability. It is demonstrated that time-resolved fluorescence spectroscopy is a sensitive and direct measurement to follow the observed changes. Overall, this study demonstrates the interplay between thermodynamics and kinetics in materials synthesis and the impact on crystal phase formation and properties.Funding for open access charge: CRUE-Universitat Jaume

Unraveling the superior role of dicarboxylic acids as surface chelators in Eu3+-doped yttrium fluorides: A systematic modulation of the crystal phases and morphologies for highly tuned optical performance

Eu3+-doped YF3 and KY3F10 phosphors have been prepared hydrothermally in a wide range of pH values without the use of surface chelators and adding oxalic or tartaric acid. We have proved, for the first time, the usefulness of dicarboxylic acids to modulate the evolution of the surface and crystal phases in the KF-YF3 system. The morphologies and crystal structures of the materials displayed a critical dependence on the pH and the chelator employed, and a plausible mechanism to explain the differences among the distinct series of samples is proposed. As a result, the fluorides exhibited outstanding and tunable photoluminescence, with extremely high quantum efficiencies and very long lifetimes. The asymmetry ratio and Judd-Ofelt parameters calculations allowed us to establish a relationship between the optical performance of the compounds and their physicochemical properties. We feel that this study can arouse widespread interest within the materials engineering community, since similar procedures could be implemented to the extended family of complex yttrium/lanthanide fluorides for advanced applications in important fields such as bioanalytics, biomedics, or photonics. Indeed, the materials in the present work, with orangish-yellow colored emissions, could be very interesting for application in white light emitting diodes through their combination with blue chips

A new series of environment-friendly reddish inorganic pigments based on AFeO3 (A = Ln, Y) with high NIR solar reflectance

Environment-friendly pigments based onAFeO3(A¼La, Pr, Nd, Sm, Gd, Tb, Y or Yb) with high near-infrared (NIR) reflectance were synthesised by a coprecipitation method at 1200 C. The Rietveldrefinement analysis showed single-phase orthorhombic perovskite for all compositions. All pigments,which showed reddish hues, offered good colour stability after mixing these pigments in powder formwith siloxane transparent paint and two different glazes. The powderepaint mixtures produced withGdFeO3, TbFeO3and YFeO3pigments have the highest NIR solar reflectance, reaching values ofR¼50%.The temperature shielding studies conducted using TbFeO3pigmentepaint mixture for a roof coatingyielded a reduction of 3.2 C in comparison to a commercial pigment. Moreover, the glazes that werepigmented using GdFeO3, TbFeO3and YFeO3compositions also presented the most intense reddishcolours. A study of the thermal and chemical stability of the pigment with the highest NIR solarreflectance showed good stability in both cases. The reddish pigments that were prepared can thereforebe good candidates for use in different applications such as cool pigments or pigments for ceramic glazesat high temperatures

The influence of Ca2+ and Zn2+ doping on the development of sustainable pigments based on GdFeO3 perovskite: From a reddish colour towards a pure black

Black pigments are very commonly used and arouse widespread interest in the ceramic industry. Nevertheless, these pigments contain toxic elements that are detrimental to human health. In view of this, the present work is focused on the development of sustainable black pigments prepared by a coprecipitation method at 1200 °C. Samples with the nominal formula (Gd1–xCax)(Fe0.95Zn0.05)O2.975–x/2 (x = 0.00, 0.05, 0.10) showed single-phase orthorhombic perovskite. The presence of dopants played an important role in the reduction of Fe3+ to Fe2+ and caused different local distortions in the structure which explained the final black colouration of these pigments in comparison with the red GdFeO3 sample. The loss of symmetry and the increase in the number of d-d transitions of iron may explain the aforementioned changes. Co-doped pigments reached low C* values, improving on the purest black colour obtained in a commercial black ceramic pigment, which contains toxic elements. In addition to presenting good NIR solar reflectance values of up to 8%, the final colours of these pigments were also stable after their application in a commercial transparent glaze at 1080 °C that could be used for tiles.Funding for open access charge: CRUE-Universitat Jaume

Impedance spectroscopy: A useful technique to unveil the mechanism of a CO oxidation reaction

In this work, the impedance spectroscopy (IS) technique was used to aid inunderstanding the reaction mechanism of the CO oxidation reaction using thePr2Zr2−xFexO7±δ(x=0 and 0.10) mixed oxide as a heterogeneous catalyst. Thecatalytic reaction occurred in the same temperature range where there was adecrease in the overall resistivity of the materials. Moreover, it has been observedthat within the temperature range where the catalytic process takes place, thereis a variation in theAandnparameters of the power law dispersion. CombiningIS with catalytic reactions offers a robust approach to enhance the understand-ing of the mechanisms involved in the CO oxidation reaction. It enables preciseanalysis of the changes that take place at the solid–gas interface, particularly thegeneration of reactive oxygen species. Furthermore, it allows examining the rela-tionship between the presence of oxygen vacancies and defects, which directlyimpact the catalytic process.Funding for open access charge: CRUE-Universitat Jaume

Study of nanoparticles based on Cr and Sb doped TiO2 as pigments for inkjet technology applications

Nanoparticles of the ceramic pigment with composition Ti0.97Cr0.015Sb0.015O2 were prepared by microemulsion-mediated solvothermal method at 180 ºC. Anatase or rutile single phase was obtained depending on the synthesis conditions. Scanning electron microscope analysis showed the formation of nanospheres with particle size around 600 nm. The anatase to rutile transformation temperature was determined by Raman spectroscopy. The evolution of the colour was studied, and it was related with the polymorphic transition. Yellow nanopigments were obtained at low temperature and huge orange colour was observed at high temperature. Nanopigments prepared at 180 ºC were tested with an industrial frit. Similar chromatic coordinates of an industrial orange ceramic pigment obtained at high temperatures were observed. -potential values of the nanoparticles were -57 mV. The size, shape, colour and electrostatic stability of these nanoparticles make them potential candidates to be applied in glazes or inkjet printers as orange ceramic pigments.We thank the “Universitat Jaume I”-project No. P1 1B2013-65 (MJ, MD, HB, EC) for financial suppor

Environmental-friendly yellow pigment based on Tb and M (M = Ca or Ba) co-doped Y2O3

A yellow inorganic ceramic pigment with general formula Y1.86−xMxTb0.14O3−x/2 (M = Ca and/or Zn) with x = 0.06, 0.32 and 0.64 were synthesized by a modified Pechini method. XRD, SEM and HRTEM/EDX analysis showed the formation of solid solution at 1300 °C when x = 0.06 and 0.32. The best b* yellow coordinates were obtained for Ca and Zn co-doped Y1.86Tb0.14O3 samples. The intensity of the yellow colour in the samples is related to the presence of Tb4+ ions. Samples with higher concentration of Tb4+ ions lead to a better yellow colour. The chemical stability of these pigments was determinate in an industrial glaze. The glazing tests indicated that the powder samples with x = 0.06 and 0.32 fired at 1300 °C were stable in the glaze. These results make it a potential candidate for environmental friendly yellow ceramic pigment to be used in applications such as pigment for glazes or inkjet printers.We thank the “Bancaja-Universitat Jaume I” – project No. P1 1B2011-25 (MP, HB, EC) for financial support. We also thank to the SCIC “Servicios Centrales de Instrumentación Científica” and ITC “Instituto de Tecnología Cerámica” of the Jaume I University for the facilities in the different techniques. VDL thanks “Ministerio de Ciencia e Innovación” for the research contract