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Hexagonal as well as tetragonal rare earth oxycarbonates can act as hosts for optically active ions; hence, the knowledge of the structural modifications occurring when foreign hosts are inserted into the parent compound is of fundamental importance for the design of new phosphors. In this article, a phase stability study of the pseudobinary system GdOCO-NdOCO at P = 1 atm. CO between 420 and 850 °C is presented, to study the amplitude of the existence fields of the different structures typical of rare earth oxycarbonates. The samples were prepared by thermal decomposition of the corresponding oxalates in CO atmosphere. According to composition and temperature, all the three structural forms reported for oxycarbonates (hexagonal, tetragonal, and monoclinic) have been observed. Above a certain temperature, that depends on composition and increases with Nd amount, all the samples decompose into the corresponding Gd-Nd-mixed oxides and crystallize into one of the three possible structural forms typical of rare earth sesquioxides. Structural refinements performed on the hexagonal oxycarbonates demonstrate that the insertion of Nd in GdOCO results in a linear increase of the lattice parameters (Vegard's law) and in a reorganization of the distances between and in the CO groups and the (Nd/GdO) layers. [ABSTRACT FROM AUTHOR]

Abstract: X-ray absorption measurements have been made on CuL3 and OK edges for two transition metal substituted Hg based oxycarbonates Hg0.5Mo0.5Sr4Cu2(CO3)O6+ δ and Hg0.4Cr0.6Sr4Cu2(CO3)O6+ δ . Despite a much lower T c (37K) the Cr sample has a much higher diamagnetic fraction than the Mo sample (T c∼74K). CuL3 and OK edge spectra clearly indicate the presence of substantial number of doping holes in both the samples characteristic of their superconducting properties. But interestingly, the density of holes (DOH) are almost the same for the two samples. If the DOH correlated with the T c solely, one would expect it be nearly double in Mo sample than the Cr one. Thus the present study presents a strong evidence for the dependence of DOH upon diamagnetic fraction over and above its dependence upon their transition temperature in the cuprate perovskites. Also the results of resistivity and susceptibility studies made earlier on these samples have been mentioned briefly. [Copyright &y& Elsevier]

The phases present in the Tl2O3–MO system, where M=Ca and Sr, have been synthesised and characterised using powder neutron diffraction data. The structures of the phases known to exist in the CanTl2O3+n system with n=1, 1.5, 2 and 3 have been refined and the oxycarbonate phase with composition Ca4Tl2O6CO3 has been identified. In the SrnTl2O3+n system, the structures of the phases with n=1, 2 and 3 have also been refined. The MnTl2O3+n phases with M=Ca and Sr and n=1–3 are related to the lillianite structure while the n=4 compound is an oxycarbonate that has been found to crystallise in I4/mmm symmetry for M=Ca and in three different modifications with space groups P4/mmm, I4/mmm and Pmmm for M=Sr, depending on the ordering of the carbonate groups. The relationships between these structures are discussed and comparisons are made to the previously published structures determined from X-ray powder diffraction data. [Copyright &y& Elsevier]

Arrangements of carbonate groups (CO3) in various 'oxycarbonate' superconductors, prepared mainly by high pressure of around 5GPa, are investigated by high-resolution transmission electron microscopy (HRTEM). Many of these oxycarbonate structures are derived simply by replacing parts of the metal sites of some parent 'oxide' structures by CO3. Unique new structures, such as (Cu,C)-23(n-1)n series of superconductors in a Ba-Ca-Cu-C-O system, have also been discovered. In the case where the 'conduction' block of the parent oxide consists of a Ca-based 'infinite-layer' structure, the CO3 triangles. In contrast, in the case where the conduction block has an Sr-based structure without Ca, on the other hand, CO3 groups can replace every second CuO2 layers of the conduction block, because the apical oxygen can be accepted to form SrO layers. Complicated superstructures are often formed when the CO3 replacements are combined with additional crystallographic-shear operations, as observed in both Hg- and Tl-based oxycarbonates. Finally, local formations of planar defects by CO3 invasions are observed even in some 'oxide' superconductors prepared under high-pressure conditions. [ABSTRACT FROM PUBLISHER]

Nanomaterials with persistent luminescence (PLNMs) have emerged as important materials in autofluorescence-free detection for their exceptional ability to temporarily detach the excitation and emission procedure. Although significant advances in materials composition have been made, research of morphology-dependent PLNMs synthesis is still lacking. At its core, further understanding toward the morphology optimization and afterglow enhancement is needed for their future expansion. Herein, we report a two-step synthesis to prepare morphology and afterglow controllable persistent luminescent oxycarbonates (La 2 O 2 CO 3 : Eu3+, Ho3+). In step one, we emphasized a precipitation pretreatment to ensure uniform precursor nanorods. Then, a morphology evolution from nanorods through bamboo-like nanorods to nanoparticles as well as the control of afterglow time can be realized by simply changing posttreatment conditions, such as reaction duration and reaction power. In particular, we highlighted the nanoparticles can be easily produced via cutting the bamboo-like nanorod section by section during the effortless mechanical grinding. In addition, the as-obtained PLNMs exhibit an excellent aqueous stability and remain suspended in adtevak from live mouse and 10% glucose beyond 10 days. The experiment of autofluorescence-free H 2 O 2 detection with La 2 O 2 CO 3 : Eu3+, Ho3+ PLNMs employed as sensing probe demonstrates that these PLNMs present a fresh way of using PLNMs as a new H 2 O 2 detection mode without in situ excitation for real time monitoring of H 2 O 2 and glucose. • Synthesized a biocompatible material La2O2CO3: Eu3+ via a simple precipitation method. • A red persistent luminescence appears after ceasing the excitation at 254 nm UV light. • Morphologies and afterglow can be controlled by changing post-treatment conditions. • The La2O2CO3 material display a remarkable stability. [ABSTRACT FROM AUTHOR]

We have synthesised a series of compounds in both the (PbTl)Sr4Cu2O7(CO3)1−y(NO3)y (0.1≤y≤0.5) and TlSr2Ba2Cu2O7(CO3)1−y(NO3)y (0.1≤y≤0.2) systems. We report the synthesis conditions of these materials, an X-ray diffraction analysis of their structure and the changes induced in superconducting behaviour produced by the introduction of nitrate groups into the starting composition. [ABSTRACT FROM AUTHOR]

A series of luminescent rare-earth ion-doped hexagonal II-type Gd oxycarbonate phosphors Gd2-xRExO2CO3 (RE = Eu(3+), Yb(3+), Dy(3+)) have been successfully synthesized by thermal decomposition of the corresponding mixed oxalates. The Yb(3+) doped Gd-oxycarbonate has evidenced a high persistent luminescence in the NIR region, that is independent from the temperature and makes this materials particular attractive as optical probes for bioimaging.