M5 Sites Research Articles

Distribution of Eu and Er in Ca9RE(PO4)7 phosphors analyzed by anomalous X-ray scattering

The structures of Ca9Eu(PO4)7 and Ca9Er(PO4)7 phosphors were analyzed using single-crystal X-ray diffraction. Most Eu ions reside at the medium-sized M1 and M2 sites, with a small amount occupying the M5 site. In contrast, the smaller Er ions favor the smallest M5 site. This study also demonstrates the use of anomalous X-ray scattering measurements at the Er LIII and Er LIII-edges. The energy dependencies observed in the scattering factors for Ca9Eu(PO4)7 and Ca9Er(PO4)7 confirmed the preferred distribution of Eu and Er. Because this anomalous X-ray scattering method leverages the unique anomalous dispersion terms of each element, this advanced technique, coupled with a synchrotron radiation source, is suggested to be a powerful method for distinguishing near-neighbor rare-earth elements in solid-state phosphors.

Strontium and Copper Co-Doped Multifunctional Calcium Phosphates: Biomimetic and Antibacterial Materials for Bone Implants.

β-tricalcium phosphate (β-TCP) is a promising material in regenerative traumatology for the creation of bone implants. Previously, it was established that doping the structure with certain cations can reduce the growth of bacterial activity. Recently, much attention has been paid to co-doped β-TCP, that is explained by their ability, on the one hand, to reduce cytotoxicity for cells of the human organism, on the other hand, to achieve a successful antibacterial effect. Sr, Cu-co-doped solid solutions of the composition Ca9.5-xSrxCu(PO4)7 was obtained by the method of solid-phase reactions. The Rietveld method of structural refinement revealed the presence of Sr2+ ions in four crystal sites: M1, M2, M3, and M4. The M5 site is completely occupied by Cu2+. Isomorphic substitution of Ca2+ → (Sr2+and Cu2+) expands the concentration limits of the existence of the solid solution with the β-TCP structure. No additional phases were formed up to x = 4.5 in Ca9.5-xSrxCu(PO4)7. Biocompatibility tests were performed on cell lines of human bone marrow mesenchymal stromal cells (hMSC), human fibroblasts (MRC-5) and osteoblasts (U-2OS). It was demonstrated that cytotoxicity exhibited a concentration dependence, along with an increase in osteogenesis and cell proliferation. Ca9.5-xSrxCu(PO4)7 powders showed significant inhibitory activity against pathogenic strains Escherichia coli and Staphylococcus aureus. Piezoelectric properties of Ca9.5-xSrxCu(PO4)7 were investigated. Possible ways to achieve high piezoelectric response are discussed. The combination of bioactive properties of Ca9.5-xSrxCu(PO4)7 renders them multifunctional materials suitable for bone substitutes.

Synthesis, dopant solubility, and thermostructural properties of Ca10.5-xTMx(VO4)7 (TM = Co, Cu) as function of transition metal content.

Crystals of Ca10.5-xTMx(VO4)7 (TM = Co, Cu), belonging to the whitlockite family, were synthesized by solid-state reaction and studied as a function of the TM content (x) for the first time. The structure was refined at ambient conditions and at high temperatures up to 1200 K using the Rietveld method. The unit cell size significantly decreases with increasing TM content up to the solubility limit, xlim, which is 0.78(3) for TM = Co and 0.75(4) for TM = Cu. Occupancy factors show a preference for the M5 site by Co/Cu. The unit cell size varies smoothly with temperature, while the axial ratio exhibits nonlinear behaviour above approximately 800 K. The thermal expansion coefficient was determined from 300-1100 K. Atomic arrangement modifications at higher temperatures are indicated by changes in the axial ratio, the thermal expansion coefficient, and the reduction of fractional TM occupancy at the M5 site at specific temperatures.

Antimicrobial and Cell-Friendly Properties of Cobalt and Nickel-Doped Tricalcium Phosphate Ceramics.

β-Tricalcium phosphate (β-TCP) is widely used as bone implant material. It has been observed that doping the β-TCP structure with certain cations can help in combating bacteria and pathogenic microorganisms. Previous literature investigations have focused on tricalcium phosphate structures with silver, copper, zinc, and iron cations. However, there are limited studies available on the biological properties of β-TCP containing nickel and cobalt ions. In this work, Ca10.5-xNix(PO4)7 and Ca10.5-xCox(PO4)7 solid solutions with the β-Ca3(PO4)2 structure were synthesized by a high-temperature solid-state reaction. Structural studies revealed the β-TCP structure becomes saturated at 9.5 mol/% for Co2+ or Ni2+ ions. Beyond this saturation point, Ni2+ and Co2+ ions form impurity phases after complete occupying of the octahedral M5 site. The incorporation of these ions into the β-TCP crystal structure delays the phase transition to the α-TCP phase and stabilizes the structure as the temperature increases. Biocompatibility tests conducted on adipose tissue-derived mesenchymal stem cells (aMSC) using the (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) (MTT) assay showed that all prepared samples did not exhibit cytotoxic effects. Furthermore, there was no inhibition of cell differentiation into the osteogenic lineage. Antibacterial properties were studied on the C. albicans fungus and on E. coli, E. faecalis, S. aureus, and P. aeruginosa bacteria strains. The Ni- and Co-doped β-TCP series exhibited varying degrees of bacterial growth inhibition depending on the doping ion concentration and the specific bacteria strain or fungus. The combination of antibacterial activity and cell-friendly properties makes these phosphates promising candidates for anti-infection bone substitute materials.

Mn2+ Luminescence in Ca9Zn1-xMnxNa(PO4)7 Solid Solution, 0 ≤ x ≤ 1.

The solid solution Ca9Zn1-xMnxNa(PO4)7 (0 ≤ x ≤ 1.0) was obtained by solid-phase reactions under the control of a reducing atmosphere. It was demonstrated that Mn2+-doped phosphors can be obtained using activated carbon in a closed chamber, which is a simple and robust method. The crystal structure of Ca9Zn1-xMnxNa(PO4)7 corresponds to the non-centrosymmetric β-Ca3(PO4)2 type (space group R3c), as confirmed by powder X-ray diffraction (PXRD) and optical second-harmonic generation methods. The luminescence spectra in visible area consist of a broad red emission peak centered at 650 nm under 406 nm of excitation. This band is attributed to the 4T1 → 6A1 electron transition of Mn2+ ions in the β-Ca3(PO4)2-type host. The absence of transitions corresponding to Mn4+ ions confirms the success of the reduction synthesis. The intensity of the Mn2+ emission band in Ca9Zn1-xMnxNa(PO4)7 rising linearly with increasing of x at 0.05 ≤ x ≤ 0.5. However, a negative deviation of the luminescence intensity was observed at x = 0.7. This trend is associated with the beginning of a concentration quenching. At higher x values, the intensity of luminescence continues to increase but at a slower rate. PXRD analysis of the samples with x = 0.2 and x = 0.5 showed that Mn2+ and Zn2+ ions replace calcium in the M5 (octahedral) sites in the β-Ca3(PO4)2 crystal structure. According to Rietveld refinement, Mn2+ and Zn2+ ions jointly occupy the M5 site, which remains the only one for all manganese atoms within the range of 0.05 ≤ x ≤ 0.5. The deviation of the mean interatomic distance (∆l) was calculated and the strongest bond length asymmetry, ∆l = 0.393 Å, corresponds to x = 1.0. The large average interatomic distances between Mn2+ ions in the neighboring M5 sites are responsible for the lack of concentration quenching of luminescence below x = 0.5.

Crystal Structure, Thermal Expansion and Luminescence of Ca10.5−xNix(VO4)7

The structural and luminescence properties of a new material, Ca10.5−xNix(VO4)7, formed by substitution of a fraction of calcium by nickel, are studied as a function of the Ni content (x). The powder X-ray diffraction results for the polycrystals, synthesized using a solid-state reaction method, show that in the studied temperature range (300–1150 K), the structure of the unsubstituted material (space group R3c, whitlockite-β-Ca3(PO4)2 structure type) is conserved up to the solubility limit, x = 0.72(2), determined on the basis of variation of unit cell size with x. The samples of nominal composition exceeding this limit contain a significant amount of the impurity phase.The structural refinements demonstrate that Ni atoms preferentially occupy the M5 site (one of the five independent Ca sites, M1–M5). The unit cell size was equally studied in the range of 300–1150 K, leading to the determination of the thermal expansion coefficients. It was found that with rising Ni content, the room temperature volumetric thermal expansion decreases from 41.80 MK−1 (x = 0.16) to 39.24 MK−1 (x = 0.66) and to 38.92 MK−1 at the solubility limit, this reduction being in line with earlier reported data for x=0. In the unit cell variation, around 800–900 K, a weak anomaly is observed, detectable most clearly for the axial ratio; it is also visible at thermal expansion coefficient temperature dependence. Substitution of Ca by Ni ions reduces the optical band gap of Ca10.5−xNix(VO4)7 from 3.56 (x = 0) to 3.29 and 3.16 eV observed for Ni-containing samples (x = 0.33 and 0.66, respectively). Observed bands in the absorption and photoluminescence spectra are assigned to electronic transitions in both VO43− groups and Ni2+ ions, confirming that Ni mainly occupies the M5 site. The band gap narrowing and decrease in photoluminescence intensity when the Ni concentration increases makes Ni-substituted compounds attractive for application, e.g., as photocatalysts.

Dependence of antimicrobial properties on site-selective arrangement and concentration of bioactive Cu2+ ions in tricalcium phosphate

Cu-doped solid solutions Ca10.5–xCux(PO4)7 with β-Ca3(PO4)2 (β-TCP) structure were synthesized using high-temperature solid-state synthesis. Correctly characterizing the location of Cu2+ in the structure is important for a correct understanding of the biological properties formation. The limit of Ca10.5–xCux(PO4)7 solid solutions without impurity phases was found at x = 1.5. The crystal-chemical analysis reveals that the Cu2+ ions cannot be located in the M4 site of the β-TCP-type structure due to the very distorted environment. The Cu2+ ions preferably occupy the M5 site (x ≤ 1.00) and then located in the M3 and M2 sites (x > 1.00). The chemical composition, local environment, and structural features of Ca10.5–xCux(PO4)7 phosphates were investigated by a complex of methods. The antibacterial properties were studied on one fungus (C. albicans) and four bacteria (E. coli, E. faecalis S. aureus and P. aeruginosa). Biocompatibility tests were performed on human bone marrow mesenchymal stem cells (hMSCs). The biological response of the Cu2+ strongly depends on the occupied ion position and its concentration. The concentration-dependent behavior of the bacteria growth inhibition was observed, and the sample with x = 1.33 exhibits the highest activity between single-phase samples. Further increasing of bacteria growth inhibition is attributed to Ca3Cu3(PO4)4 impurity phase. Also, antimicrobial properties depend on the Cu2+ location in the β-TCP crystal structure in accordance with ion release behavior. The Cu2+ location in the large M3 polyhedra leads to a noticeable increase in ion release. Biocompatibility assays on hMSCs showed the absence of cytotoxicity in direct and indirect contact for single-phase samples. In the biphasic sample the presence of impurity Ca3Cu3(PO4)4 phosphate at 2 wt% causes a cytotoxicity effect. Thus, phase purity plays a critical role in understanding the regularities of bioactive properties formation. This work can be an initial basis for further investigations of the site-selective arrangement of bioactive ions, such as Cu2+ and other similar ions, in the β-TCP structure to enhance biological potential.

Zhanghuifenite, Na3Mn42+Mg2Al(PO4)6, a new mineral isostructural with bobfergusonite, from the Santa Ana mine, San Luis province, Argentina

Abstract A new mineral species, zhanghuifenite, ideally Na3Mn42+Mg2Al(PO4)6, has been found in the Santa Ana mine, San Luis province, Argentina. It occurs in irregular veinlets or patches, 5 mm thick, in a nodule of beusite interlaminated with lithiophilite. Broken pieces of zhanghuifenite are blocky or tabular. Single crystals are up to 0.8 × 0.5 × 0.5 mm. No twinning or parting is observed macroscopically. The mineral is deep green, transparent with pale green streak and vitreous luster. It is brittle and has a Mohs hardness of ~5 with good cleavage on {010}. The measured and calculated densities are 3.63(2) and 3.62 g/cm3, respectively. Optically, zhanghuifenite is biaxial (+), with α = 1.675(2), β = 1.680(2), γ = 1.690(2) (white light), 2V (meas) = 74(2)°, and 2V (calc) = 71°. The calculated compatibility index based on the empirical formula is 0.020 (excellent). An electron microprobe analysis yields an empirical formula (based on 24 O apfu) (Na2.80Ca0.11)Σ2.91(Mn3.092+Fe0.472+Mg0.36)Σ3.92(Mg1.31Fe0.692+)Σ2.00 (Al0.81Fe0.193+)(PO4)6. Zhanghuifenite is insoluble in water or hydrochloric acid. Zhanghuifenite is isostructural with bobfergusonite, a member of the alluaudite supergroup. It is monoclinic, with space group P21/n, Z = 4, and unit-cell parameters a = 12.8926(3), b = 12.4658(3), c = 10.9178(2) Å, β = 97.9200(10)°, and V = 1737.93(7) Å3. The crystal structure of zhanghuifenite contains six octahedral M (= Mn, Fe, Mg, Al) sites and five X (= Na, Mn, Ca) sites with coordination numbers between 6 and 8. The six M octahedra share edges to form two types of kinked chains extending along [101], with one consisting of M1-M4-M5 and the other M2-M3-M6. These chains are joined by PO4 tetrahedra to form sheets parallel to (010), which are linked together through corner-sharing between PO4 tetrahedra and MO6 octahedra in the adjacent sheets, leaving open channels parallel to a, where the large X cations are situated. Zhanghuifenite differs from bobfergusonite in two major aspects. One is that the M4 and M5 sites in the former are mainly occupied by Mg, but by Fe2+ and Fe3+, respectively, in the latter. The other is that the X2-X5 sites in zhanghuifenite are all nearly or fully filled with Na, resulting in 3 Na apfu in the ideal formula, but X4 and X5 are merely half-occupied in bobfergusonite, giving rise to 2 Na apfu.

Crystal structure, dielectric and optical properties of β-Ca3(PO4)2-type phosphates Ca9-xZnxLa(PO4)7:Ho3+

A series of new phosphates Ca9-xZnxLa(PO4)7:Ho3+ with the β-Ca3(PO4)2-type structure was synthesized by the solid state route. An intense near infra-red (NIR) emission according to intraconfigural 4f-4f transitions of Ho3+ ions 5I7 – 5I8 (~2 μm) and 5I6 – 5I8 (~1.156 μm) was observed. The obtained phases were studied by a combination of methods including synchrotron powder X-ray diffraction, dielectric spectroscopy, second harmonic generation, differential scanning calorimetry, luminescence spectroscopy. The structure of Ca8ZnLa(PO4)7 was refined by the Rietveld method in centrosymmetric space group R3‾c. The Ca2+ → Zn2+ substitution in the M5 site leads to a transformation from polar R3c space group (x = 0 – 0.5) to centrosymmetric R3‾c space group (x = 0.6–1) and to the increased integral intensity of luminescence with maxima at x = 1. It was concluded that the crystal site engineering in the Ho3+-containing β-Ca3(PO4)2-type hosts offers a promising way to obtain new NIR phosphors for use in the creation of biocompatible bone tissue fillers.

The crystal structure and thermal expansion of novel substitutionally disordered Ca10TM0.5(VO4)7 (TM = Co, Cu) orthovanadates.

The whitlockite-related materials have attracted researchers' attention because of their potential application in various fields, especially in optoelectronics. In the present work, the structure of novel whitlockite-related oxides Ca10TM0.5(VO4)7 (TM = Co, Cu) is studied at room and high temperatures, using X-ray powder diffraction. These compounds form by fractional substitution of divalent transition metal atoms into the Ca3(VO4)2 lattice. Rietveld refinements provided the structural details. The lattice parameters are a = 10.78074(6) Å, c = 37.8196(2) Å, and V = 3806.67(4) Å3 for Ca10Co0.5(VO4)7 and a = 10.78710(7) Å, c = 37.8997(3) Å, and V = 3819.23(4) Å3 for Ca10Cu0.5(VO4)7. Structure refinement results show that among the five available sites (M1-M5), the M2+ ions select the M5 site. This finding is confirmed by analysis of interatomic distances: due to the difference in size between TM and Ca ions sharing the M5 site, the M5-O distance shortens by about 5.0% for Ca10Co0.5(VO4)7 and 2.7% for Ca10Cu0.5(VO4)7 with respect to the unsubstituted parent compound, Ca3(VO4)2. The observed trends in the crystallographic properties of the studied crystals are in line with those of previously reported structurally related phosphates, Ca10.5-xMx(PO4)7 (M = Mg or divalent transition metal). Moreover, the observed tendency for occupation of M5 by small divalent ions follows the earlier theoretical results. For cobalt and copper substituted orthovanadate and orthophosphate whitlockite related materials, a linear variation in the unit cell size is demonstrated. The common equation for evaluation of volume is applicable to the substitution of the two transition metals in orthovanadate and orthophosphate whitlockite related materials. Thermal expansion is investigated for both compounds. The variations of the lattice parameters and the thermal expansion coefficient with temperature are determined in the 300-810 K range. The lattice parameter, a, expands by 0.80% for Ca10Co0.5(VO4)7 and 0.74% for Ca10Cu0.5(VO4)7 in this range. The lattice parameter, c, enlarges by about 0.70% for both samples. In the studied temperature range, the volume thermal expansion coefficient of Ca10Co0.5(VO4)7 increases from 37.2 to 44.8 MK-1 and for Ca10Cu0.5(VO4)7, it increases from 35.1 to 45.2 MK-1; the observed expansion anisotropy is smaller than those of other related compounds.

Superstructure formation in a ternary Yb-Cd-Mg 1/1 quasicrystal approximant

ABSTRACT The superstructure and basic structure of ternary Yb-Cd-Mg 1/1 quasicrystal approximants with the compositions YbCdMg and YbCdMg were investigated using X-ray structural analysis. The former was determined to have a face-centred packing structure comprising two distinguishable Tsai-type rhombic triacontahedron clusters (space group , Å), while the latter was found to have a body-centred packing structure made of identical Tsai-type rhombic triacontahedron clusters (space group , Å). The distinction between the two types of clusters in the superstructure is based on the positional disorder of the first tetrahedron shell and the relative Cd/Mg occupancy at M5 sites in the fourth icosidodecahedron shell. In both the superstructure and basic structure, sites preferentially occupied by Mg typically have two Yb atoms among the atoms to which they are coordinated. Finally, a six-dimensional structural model of the primitive Tsai-type icosahedral quasicrystals was modified so as to incorporate the selective Cd/Mg occupation found in the 1/1 approximants.

Structure and electronic properties of CaAl12−xFexO19 hibonites

Dilution of iron in the AM12O19 has shown promising coupling of magnetic and electric properties in the hexaferrites. We have prepared samples of low iron content in the isostructural hibonite, CaAl12−xFexO19, to investigate the structural effects of larger iron substitution into the aluminum sites and the resultant properties. We found a solid solution exists for CaAl12−xFexO19 where x ≤ 5.5. Iron distributes into all sites with the tetrahedral M3 and octahedral M5 sites displaying nominally larger preference at higher Fe content. Paramagnetic behavior was observed for x ​= ​1–3, while x ​= ​4–5.5 displayed a broad ferromagnetic-like transition with increasing Curie temperature. Differences in field-cooled and zero-field-cooled magnetic susceptibility measurements and low magnetic moment indicate the presence of a frustrated antiferromagnetic structure as the source of the ferromagnetic-like behavior. Increasing Fe content also increases the dielectric constant up to 21 ​at room temperature with high dielectric loss.

Synthesis, neutron diffraction and photoluminescence properties of a whitlockite structured Ca9MgLi(PO4)7:Pr3+ phosphor

The whitlockite structured compound Ca9MgLi(PO4)7 has been investigated as a potential host material for down-conversion phosphors. However, no detailed crystal structure and crystallographic site occupancy have been reported for this compound previously. In this work, Pr3+ activated Ca9MgLi(PO4)7 phosphors were successfully synthesized, and the structure and photoluminescence properties were characterized. Upon neutron and X-ray powder diffraction data, the crystallographic site occupancies of M1-M5 in the whitlockite-type structure were carefully refined by the Rietveld method. The M1, M2 and M3 sites are all found to be 8-fold coordinated and fully occupied with Ca and Pr. The results also revealed that the M4 and M5 sites are co-occupied by Li–Mg and Ca–Mg, respectively. Photoluminescence (PL) study showed that the phosphor has a characteristic excitation band at the visible light region of 430–500 nm. Three peaks observed at 442, 468, and 484 nm in the excitation spectra can be ascribed to the 3H4→3P2, 3H4→3P1, and 3H4→3P0 transition of Pr3+, respectively. The phosphor doped with 0.02 Pr3+ gives the strongest emission peaked at 612 nm, with the CIE chromaticity coordinate of (0.613, 0.366). This reddish-orange emitting phosphor has good thermal stability that it retains 83% of its emission intensity at 200 °C. Energy transfer mechanism of the activators was analyzed to be dipole-dipole multipolar interaction. The present work demonstrates that Ca9MgLi(PO4)7:Pr3+ is a promising phosphor for blue-pumped white light-emitting diodes (WLEDs).

Luminescence, structure and antiferroelectric-type phase transition in Ca8ZnEu(PO4)7

Photoluminescence excitation and emission spectra of new phosphate Ca8ZnEu(PO4)7 have been investigated. The influence of the composition on the luminescence intensity has been shown. The substitution of Zn2+ for Ca2+ in Ca9Eu(PO4)7 with the formation of Ca8ZnEu(PO4)7 leads to the increased emission intensity 5D0 → 7F2 by about 1.5 times and to decreased number of bands from three to one in the range of 5D0 → 7F0 transition. Conditions of preparation do not influence the luminescent properties and distribution of Eu3+ cations in the structure. DSC, SHG data and dielectric spectroscopy reveal that Ca8ZnEu(PO4)7 belongs to antiferroelectrics (Tc = 836 K). The first-order antiferroelectric/paraelectric transformations are accompanied by a changing symmetry (R3¯с to R3¯m). The structure of Ca8ZnEu(PO4)7 (sp. gr. R3¯с) was refined by the Rietveld method. The Zn2+ cations occupy the M5 site. The Eu3+ and Ca2+ ions are located in the M1 and M3 sites of β-Ca3(PO4)2-type structure.

Pure, lithium- or magnesium-doped ferroelectric single crystals of Ca9Y(VO4)7: cation arrangements and phase transitions

Abstract Single crystals of Ca9Y(VO4)7 (1), Ca9Y(VO4)7:Li+ (2) and Ca9Y(VO4)7:Mg2+ (3) were grown by the Czochralski method. Their chemical composition was analyzed by ICP spectroscopy and their crystal structure was examined by single crystal X-ray analysis. The crystals are characterized by trigonal symmetry, space group R3c. Hexagonal unit-cell parameters are as follows: a=10.8552(1) Å, c=38.0373(2) Å, V=3881.65(1) Å3 for 1; a=10.8570(1) Å, c=38.0161(3) Å, V=3880.77(4) Å3 for 2; a=10.8465(1) Å, c=38.0366(2) Å, V=3875.36(3) Å3 for 3. All crystals are characterized by β-Ca3(PO4)2-type structure with statistical distribution of Ca2+ and Y3+ over M1, M2 and M5 sites in different ratios and with completely empty M4-cationsite. The impurity of Mg2+cations in structure 2 has been detected in octahedral M5 site. Ferroelectric phase transitions are evidenced by DSC and SHG. At about 1220 and 1300 K, they demonstrate phase transitions. Upon heating the symmetry of the crystal structure changes according to the scheme R3c→R3̅c→R3̅m and is restored during consequent cooling. The first of them is of ferroelectric and the second of non-ferroelectric nature. Even a small amount of impurities in Ca9Y(VO4)7 structure is accompanied by a noticeable decrease in the temperature of the ferroelectric-paraelectric phase transition.

Tuning of photoluminescence by co-doping Eu2+, Eu3+ and Tb3+ in Ca9NaZn(PO4)7 phosphor

A series of Ca9NaZn(PO4)7: Eu2+/Eu3+, Tb3+ (CNZP: Eu2+/Eu3+, Tb3+) phosphors were synthesized by the solid-state reaction method. The results of structure refinement indicate that the chemical formula of CNZP can be written as Ca9.12(5)Zn0.88(5)Na1.0(2)(PO4)7. Ca2+ ions fully occupy M1 site and partly occupy M2, M3 and M5 sites. The M4 sites are 100% occupied by Na+ ions and Na+ ions didn't participate in other sites. Zn2+ ions partly occupy M2, M3 and M5 sites and the biggest occupation 81(2)% of Zn2+ was observed for M5 sites. There are both 6-coordinated and 8-corrdinated Ca2+ and Zn2+ in CNZP matrix. According to Davolos's theory, we speculated that Eu3+ ions could substitute both Ca2+ and Zn2+ ions in CNZP matrix, while Eu2+ ions could only replace Ca2+ ions but not Zn2+ ions in CNZP host. Eu3+ ions doped in CNZP matrix only partly were reduced to Eu2+ state under the preparation conditions. The reaction mechanism was proposed. The emission color of the as-prepared phosphor were tuned from blush-violet to warm-white and yellowish-green by energy transfer of Eu2+→Tb3+ and Tb3+→Eu3+ in CNZP: Eu2+/Eu3+, Tb3+ phosphor. The samples showed good thermal stability. All the results imply that CNZP: Eu2+/Eu3+, Tb3+ phosphor is a potential color-tunable phosphor candidate for n-UV LEDs.

Refining the Society Islands cultural sequence: colonization phase and developmental phase coastal occupation on Moʻorea Island

The Society Islands are critical to chronology building in East Polynesia, as the archipelago served as a potential first landfall for voyagers moving out of the West Polynesia homeland. Yet determining the particulars of migration sequences and settlement chronology in the Society Islands, like the rest of East Polynesia, has been challenging. Here, we report on a dating and re-dating program of four coastal sites on the island of Moʻorea, Windward Society Islands, aimed at refining the archipelago's cultural chronology and its place within larger settlement trends for East Polynesia. We begin with a brief discussion of 1960s archaeological research in the Society Islands and the archipelago's role in the East Polynesian colonisation debate before turning to a discussion of the newly dated and re-dated Mo'orea coastal sites. Our new corpus of 14C dates provides evidence for two well-studied Mo'orea Island sites dating to the Colonisation Phase (GS-1 and ScMf-5). The earliest dated occupation of the ScMf-5 site contained an earth oven, diverse artefacts and dense faunal remains indicative of a permanent, and perhaps large, settlement along the north shore of Moʻorea. Results point to established Society Island populations from the 11th to 13th centuries AD, supporting both the Conservative Model of East Polynesian settlement and more inclusive synthetic models. Developmental Phase dates from ScMf-2 illustrate that new parts of the Moʻorea north shore were inhabited at this time, while other earlier coastal sites continued to be occupied, tentatively suggesting population increase. The re-dated M5 site, with its elaborate temples of the 'Oro cult style, fits well into accepted dates for the Classic Phase. Our re-dating program has not only allowed us to refine the Society Islands cultural sequence, but has permitted precise identification or confirmation of two sites dating to the Colonisation Phase.

Antiferroelectric properties and site occupations of R3+ cations in Ca8MgR(PO4)7 luminescent host materials

Ca8MgR(PO4)7 (R = La, Pr, Nd, Sm−Lu, and Y) phosphates with a β-Ca3(PO4)2 related structure were prepared by a standard solid-state method in air. Second-harmonic generation, differential scanning calorimetry, and dielectric measurements led to the conclusion that all Ca8MgR(PO4)7 are centrosymmetric and go to another centrosymmetric phase in the course of a first-order antiferroelectric phase transition well above room temperature (RT). High-temperature electron diffraction showed that the symmetry changes from R3¯c to R3¯m during the phase transition. Structures of Ca8MgR(PO4)7 at RT were refined by the Rietveld method in centrosymmetric space group R3¯c. Mg2+ cations occupy the M5 site; the occupancy of the M1 site by R3+ cations increases monotonically from 0.0389 for R = La to 0.1667 for R = Er-Lu, whereas the occupancy of the M3 site by R3+ cations decreases monotonically from 0.1278 for R = La to 0 for R = Er-Lu. In the case of R = Er-Lu, the M3 site is occupied only by Ca2+ cations. P1O4 tetrahedra and cations at the M3 site are disordered in the R3¯c structure of Ca8MgR(PO4)7. Using synchrotron X-ray powder diffraction, we found that annealing conditions do not significantly affect the distribution of Ca2+ and Eu3+ cations between the structure positions of Ca8MgEu(PO4)7. Luminescent properties of Ca8MgEu(PO4)7 powder samples were investigated under near-ultraviolet (n-UV) light. Excitation spectra of Ca8MgEu(PO4)7 show the strongest absorption at about 395 nm that matches with commercially available n-UV-emitting GaN-based LED chips. Emission spectra show an intense red emission due to the 5D0 → 7F2 transition of Eu3+.

Site-occupancy, luminescent properties and energy transfer of a violet-to-red color-tunable phosphor Ca10Li(PO4)7: Ce3+, Mn2+

A series of color-tunable phosphors Ca10Li(PO4)7: Ce3+, Mn2+ were synthesized by high-temperature solid-state reaction. Site occupancy of Ce3+ and Mn2+ in Ca10Li(PO4)7 and corresponding luminescent properties were systemically studied. Rietveld refinement results indicate that the Ce3+ ions are preferred to occupy 7-cooridnated M1 and M3 sites, and Mn2+ ions are mainly occupying distorted octahedral M5 sites, which results in Ce3+ violet emission at 370nm and Mn2+ red emission at 640nm. The intensity of Mn2+ red emission is greatly enhanced through efficient Ce3+-Mn2+ energy transfer (ηET=94%). The critical distance and corresponding mechanism of Ce3+-Mn2+ energy transfer was found to be ~11Å and dipole-quadrupole interaction, respectively. The emitting colors of Ca10Li(PO4)7: Ce3+, Mn2+ phosphors can be tuned from violet through pink to red by adjusting the Ce3+/Mn2+ ratio. The composition-optimized red phosphor Ca10Li(PO4)7: 0.05Ce3+, 0.09Mn2+ exhibits excellent thermal stability at high temperature (~100% at 160°C).

Structural characterization and composition of Y-rich hainite from Sakharjok nepheline syenite pegmatite (Kola Peninsula, Russia)

Y-rich hainite occurs in nepheline syenite pegmatite of the Sakharjok massif (Kola Peninsula, Russia). It forms euhedral prismatic crystals up to 2 mm in length as well as rims around an unidentified mineral phase (silicate of Ca, Y, Zr and Ti). The mineral is triclinic, space group P-1, a 9.6054(10), b 5.6928(6), c 7.3344(7) Å, α 89.903(2), β 101.082(2), γ 100.830(2)°, V 386.32(7) Å3, Z = 1. The calculated density is 3.39 g/cm3. Chemical composition of Sakharjok hainite is different from the previously published data by much higher Y and Nb contents up to 0.72 and 0.20 atoms per formula unit, respectively, by the two- to five-fold depletion in the LREEs and by the strong enrichment of the HREEs. From the single-crystal X-ray diffraction data, there is a significant amount of Y in the M1 site associated with the absence of Zr in it. Nb and Zr are concentrated in the M5 site substituting Ti. Combination of single-crystal X-ray diffraction data and electron microprobe data give the empirical formula (Ca1.04Y0.63REE0.24Mn0.02)∑1.93(Na0.92Ca0.77)∑1.69Ca2.00(Na0.65Ca0.10)∑0.75(Ti0.60Zr0.21Nb0.15Fe0.03)∑0.99((Si4.00Al0.02)∑4.02O14) (F2.61O1.39)∑4.00.