Eu(iii)/Eu(ii)-doped (Ca_0.7Sr_0.3)CO₃ phosphors with vaterite/calcite/aragonite forms as shock/temperature detectors

Abstract

A pure metastable Eu(III)-doped (Ca 0.7 Sr 0.3 )CO 3 vaterite phase has been obtained by the precipitation method. After thermal treatment of this phase, the carbonate crystallizes with a calcite structure.Moreover, with the incorporation of 30 mol% of Sr that tends to stabilize the aragonite structure, both vaterite and calcite phases are able to transform easily into this high-pressure form by mechanical treatment. Hence, for this single composition, the three allotropic forms are achieved and can be compared. Photoluminescence studies indicate the stabilization of the Eu ions in the carbonates obtained, whatever the allotropic form, in the trivalent oxidation state. Significantly different luminescence properties have been found depending on the carbonate structure, which are associated with the various local environments of the doping element. This offers the possibility to employ these Eu(III)-doped samples as shock and/or temperature detectors. In addition, the use of a CaH 2 reducing agent allowed reduction of the main part of the Eu(III) content into Eu(II) in the three different carbonate forms at low temperature. Photoluminescence studies were also performed in these Eu(II)-doped samples and show slightly different emission spectra for the three crystalline structures.

Phase transitions in Mn(Mo1−xWx)O4 oxides under the effect of high pressure and temperature

“…The actual pressure transferred by the shock of the agate balls during ball milling is rather difficult to evaluate. From previous experiments on Sr 1− x Ca x CO 3 vaterite to calcite transformations achieved with the same apparatus, it was already estimated that the ball‐milling process allows phase transformation that have equivalent isostatic transition pressures reported in the literature in the range 1–10 GPa .…”

Enhanced Crystallographic Incorporation of Strontium(II) Ions into Calcite via Preferential Adsorption at Obtuse Growth Steps

“…Furthermore the coprecipitation of Sr into calcium carbonates has been proposed as an attenuation and remediation mechanism for 90 Sr contamination in groundwater [8][9][10] . 11 . Aragonite formation is favoured by high temperature/pressure environments 12 , and by the presence of Mg 2+ and SO4 2ions 6,13 . Sulphate ions compete for the carbonate site and, due to the larger sites in aragonite, sulphate hinders the growth of this polymorph the least 14 .…”

“…11 Vaterite is the least stable calcium carbonate morphology, with the central calcium atom surrounded by eight oxygen atoms with Ca−O bond lengths of 2.29−2.90 Å. 11 Aragonite formation is favored by hightemperature/high-pressure environments, 12 and by the presence of Mg 2+ and SO 4 2− ions. 6,13 Sulfate ions compete for the carbonate site, and, due to the larger sites in aragonite, sulfate hinders the growth of this polymorph the least.…”

“…Aragonite has a more open structure. The central calcium atom is surrounded by nine oxygen atoms with Ca–O bond lengths of 2.42–2.66 Å . Vaterite is the least stable calcium carbonate morphology, with the central calcium atom surrounded by eight oxygen atoms with Ca–O bond lengths of 2.29–2.90 Å .…”

“…The central calcium atom is surrounded by nine oxygen atoms with Ca–O bond lengths of 2.42–2.66 Å . Vaterite is the least stable calcium carbonate morphology, with the central calcium atom surrounded by eight oxygen atoms with Ca–O bond lengths of 2.29–2.90 Å . Aragonite formation is favored by high-temperature/high-pressure environments, and by the presence of Mg 2+ and SO 4 2– ions. , Sulfate ions compete for the carbonate site, and, due to the larger sites in aragonite, sulfate hinders the growth of this polymorph the least .…”