Photoluminescence of lanthanide-doped CaSi2O2N2 phosphors and the energy-level diagram of lanthanide ions in CaSi2O2N2

Lanthanide-doped CaSi₂O₂N₂ phosphors were synthesized by solid-state reaction. Their photoluminescence (PL) properties were investigated and analyzed systematically. Energy transitions attributed to electron transfers from 4f to 4f (ff), from 4f to 5d (fd), from 5d to 4f (df) and charge transfer (CT) transition were obtained and classified. Finally, an energy-level diagram of lanthanide-ions in CaSi₂O₂N₂ was proposed. The diagram matches perfectly with the experimental results and explains the luminescence properties of lanthanide-doped CaSi₂O₂N₂ phosphors. The electron-vibrational interaction in 4f-5d optical transitions of CaSi₂O₂N₂:Eu²⁺ was also studied.     

Photoluminescence properties of novel Eu-activated CaSi6N8O oxynitride phosphor for white LED applications

A series of novel Eu²⁺-activated CaSi₆N₈O greenish-yellow phosphors were synthesized via solid state reaction method. The synthesized CaSi₆N₈O:Eu²⁺ phosphors could absorb UV to near UV light. The emission spectra exhibited a broad greenish-yellow emission band when excited with a light of wavelength 405 nm. The emission spectrum shifted towards longer wavelength with increasing Eu²⁺ concentration. The emission intensity increased with the increasing Eu²⁺ concentration and the quenching concentration was found to be 0.1 mol. The observed results were explained by the energy transfer mechanism due to dipole-dipole interactions among Eu²⁺ ions. These novel greenish-yellow CaSi₆N₈O:Eu²⁺ phosphors could be considered as potential candidate for the white LED applications.     

Growth of ZnSiP2 from tin solution and temperature composition diagram of the ZnSiP2: Sn system

ZnSiP₂ crystals (1 cm or more in length) have been grown from tin solution on a reproducible basis. The dimensions of the largest crystals obtained were 1.7×0.25×0.03 cm³ and 2×0.1×0.02 cm³. The temperature of the reaction region was 1050 to 1080° C and the cooling rate used to form these crystals was 7.5°C h^–1.A practical temperature-composition section of the ZnSiP₂:Sn phase diagram has been determined by differential thermal analysis, X-ray diffraction measurements and microscopic studies. The resulting information on the liquidus temperature variation with composition served to give better control of ZnSiP₂ growth from tin solution. It was concluded that ZnSiP₂ reacted eutectically with Sn and the eutectic composition was close to 100%.     

Microstructure analysis of calcium phosphate formed in tendon

The surface of soft tendon tissue has been modified using calcium phosphate in order for the tendon to directly connect with hard bone and reconstruct an injured ligament. Calcium phosphate was coated onto the tendon in a soaking process using alternating a CaCl₂ (200 mM) and a Na₂HPO₄ (120 mM) solution. According to SEM/EDX observations, calcium phosphate was formed, not only on the tendon surface, but also inside the tendon tissue. When the tendon was treated with seven soaking cycles, calcium phosphate was detected between 0–500 m from the tendon surface. According to TEM observations, the crystal morphology of calcium phosphate depends on the distance from the surface. Hydroxyapatite crystals were observed near the surface, while octa-calcium phosphate crystals could be observed further from the surface, thus at initial soaking. The crystals were formed on collagen fibrils in spaces between the collagen fibrils with the c-axes of the crystals aligned parallel with the collagen fibrils. This finding suggests Ca²⁺ ions to interact with the tendon surface, most probably with the carboxyl functional groups of collagen, and subsequently forming nucleation centers for the crystals.     

Enhanced emission from CaSi2O2N2:Eu phosphors by doping with Y ions

Yttrium doped CaSi₂O₂N₂:Eu²⁺ phosphors were prepared by the solid state reaction method. Large increases in the emission have been achieved by adding Y³⁺ ions in the host. XRD data revealed that the lattice expanded as doping Y³⁺ ions. XPS results suggested that there were more Eu²⁺ ions incorporated into the lattice of Y³⁺ doped samples than that of undoped samples. The doping effect of Y³⁺ ions has been discussed systematically. By using this novel Y³⁺ doped CaSi₂O₂N₂:Eu²⁺ phosphor, bright daylight emission with luminous efficiency (η_L) of 44 lm/W, color rendering index (CRI) of 82 and correlated color temperature (CCT) of 5300 K can be generated from white LED.     

Elucidating the role of hyaluronic acid in the structure and morphology of calcium oxalate crystals

Recent surge in reports describing new additives that inhibiting the growth and nucleation of calcium oxalate (CaOx), the most common component of renal calculi or kidney stones, have rekindled interest in CaOx crystallization. In this in vitro study, the effect of hyaluronic acid (HA), a protein commonly found in urine, on the morphology and phase of the CaOx crystals is investigated. CaOx crystals were crystallized at pH 5.8 and 37 °C with a [Ca²⁺]:[C₂O₄^2-] ratio of 20:1, which is close to physiological conditions, in aqueous solution and artificial urine media. The obtained crystals were characterized structurally, morphologically and in terms of their surface charge. The crystals precipitated in aqueous solution without the HA additive were pure phase calcium oxalate monohydrate (COM) crystals with typical hexagonal morphology. The addition of HA partially promotes the transformation of COM into calcium oxalate dihydrate (COD) in aqueous solution. However, the only solid phase to form in artificial urine media with and without HA was identified as COD with tetragonal bipyramidal morphology. The results of this investigation will contribute to the understanding of the role HA plays on the morphology, structure, and thermal characteristics of CaOx and ultimately facilitate the development of effective treatments for kidney stones.     

Antibacterial and bioactive calcium titanate layers formed on Ti metal and its alloys

An antibacterial and bioactive titanium (Ti)-based material was developed for use as a bone substitute under load-bearing conditions. As previously reported, Ti metal was successively subjected to NaOH, CaCl₂, heat, and water treatments to form a calcium-deficient calcium titanate layer on its surface. When placed in a simulated body fluid (SBF), this bioactive Ti formed an apatite layer on its surface and tightly bonded to bones in the body. To address concerns regarding deep infection during orthopedic surgery, Ag⁺ ions were incorporated on the surface of this bioactive Ti metal to impart antibacterial properties. Ti metal was first soaked in a 5 M NaOH solution to form a 1 μm-thick sodium hydrogen titanate layer on the surface and then in a 100 mM CaCl₂ solution to form a calcium hydrogen titanate layer via replacement of the Na⁺ ions with Ca²⁺ ions. The Ti material was subsequently heated at 600 °C for 1 h to transform the calcium hydrogen titanate into calcium titanate. This heat-treated titanium metal was then soaked in 0.01–10 mM AgNO₃ solutions at 80 °C for 24 h. As a result, 0.1–0.82 at.% Ag⁺ ions and a small amount of H₃O⁺ ions were incorporated into the surface calcium titanate layers. The resultant products formed apatite on their surface in an SBF, released 0.35–3.24 ppm Ag⁺ ion into the fetal bovine serum within 24 h, and exhibited a strong antibacterial effect against Staphylococcus aureus. These results suggest that the present Ti metals should exhibit strong antibacterial properties in the living body in addition to tightly bonding to the surrounding bone through the apatite layer that forms on their surfaces in the body.     

Precipitation of carbonate crystal on surface active glasses

Anions, such as CO₃ ^2– and SO₄ ^2– ions, in industrial wastewater can cause serious scale problem in drainage pipes and vessels, when combined with other metal ions in the water. In this study, it was attempted to remove CO₃ ^2– ions from an aqueous solution by using surface active glasses. Glasses with various compositions of SiO₂-Na₂O-B₂O₃-RO (R = Mg, Ca, Sr, Ba) system were reacted in a CO₃ ^2– ion-containing solution with various pH, then the glass surfaces were analyzed by XRD and SEM, and CO₃ ^2– ions in the reacted solution were also measured. CO₃ ^2– ions in the solution were combined with alkaline earth metal ions, which were leached out of the glass, and were precipitated on the glass surface as carbonate crystals. In this way, the carbonate ions could be removed from the solution. The removal capacity of CO₃ ^2– ions is closely related to the surface reactivity of the glass and solubility product constants of the newly formed carbonate crystals. Glass containing either SrO or BaO showed a strong uptake capacity of CO₃ ^2– ions from the solution.     

Epitaxial growth of MgAl2O4 spinel crystals by solid-state reaction of MgO crystal with molten Al metal

Single crystals of MgAl₂O₄ spinel have been prepared epitaxially by a solid-state reaction of MgO crystal with molten Al metal under vacuum of 10^?5≈10^?6 torr at 1000≈1100°C. The growth rate was estimated to be about 0.1≈0.2 mm/hour in this temperature range. The as-grown crystals were black and opaque with low crystallinity, which was improved by heating above 1350°C. Chemical analysis showed that the crystals were slightly contaminated with Mg metal which was easily oxidized above 900°C in air.     

γ-MnS nano and micro architectures: Synthesis, characterization and optical properties

γ-MnS nanocrystalline materials have been prepared by reaction of Na₂[Mn(HL)₂(H₂O)₂]; 1:2 (M:L) chelate complex with alkaline solution of thiocarbamide in aqueous solution phase. Effect of metal chelate complex, reaction time and surfactant sodium dodecyl sulfate; SDS on phase, morphology and size of the products have been investigated. The metal chelate complex was synthesized by reacting Mn(II) ions with eriochrome black T (NaH₂L) in alkaline medium. γ-MnS crystals were formed when metal complex was used as metal source whereas Mn₃O₄ was the dominant product when MnSO₄·H₂O was used as metal source. Materials thus formed having various morphologies were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) to determine the crystallinity, phase, structure and morphology. The optical properties of the thus prepared samples were determined by UV–vis absorption spectra and photoluminescence spectra. A possible formation mechanism of crystals has been discussed in this article.     

Using a synthetic body fluid (SBF) solution of 27 mM HCO3− to make bone substitutes more osteointegrative

A Tris–HCl-buffered synthetic body fluid (SBF) solution, mimicking the human blood plasma, with the following ion concentrations of 27 mM HCO₃⁻, 2.5 mM Ca²⁺, 1.0 mM HPO₄²⁻, 142 mM Na⁺, 125 mM Cl⁻, 5 mM K⁺, 1.5 mM Mg²⁺, and 0.5 mM SO₄²⁻ was used as an aqueous medium to process a number of bone substitute materials under the so-called biomimetic conditions of 37 °C and pH 7.4. This solution was named as Tris–SBF-27 mM. Firstly, collagen sponges were soaked in Tris–SBF-27 mM solution at 37 °C and were found to be fully covered with nanoporous apatitic calcium phosphate (Ap-CaP). The composites of collagen–Ap-CaP biomaterials are expected to be used in orthopedic and dental surgery. Secondly, Ap-CaP short whiskers or microrods with a novel nanotexture and surface areas higher than 45 m²/g were synthesized in Tris–SBF-27 mM solution. Thirdly, calcium sulfate cements doped with CaHPO₄ (monetite), were shown to have apatite-inducing ability upon ageing in Tris–SBF-27 mM. CaHPO₄ addition in calcium sulfate was found to improve its mechanical strength, measured after cement setting reaction. Pure calcium sulfate cement pellets were not stable in Tris–SBF-27 mM solutions and crumbled into a powder. All the samples were characterized by SEM, XRD, FTIR, surface area and mechanical strength measurements.     

Degradation of methylene blue via photocatalysis of transition metal-loaded sulfated TiO2

Transition metal-loaded nanocrystalline SO₄²⁻/TiO₂ powders were prepared by sol–gel method. Anatase is found as the active phase in all the samples. Sulfation process clearly stabilizes TiO₂ catalyst phase against sintering, maintaining anatase phase and relatively high surface area values with respect to pure TiO₂. Wide structural and surface characterization of samples was carried out in order to establish a correlation between the effect of sulfation and metal incorporation on the TiO₂ photocatalytic properties. The maximum photocatalytic decomposition of methylene blue solution was achieved with sulfation of TiO₂. In addition, incorporation of metal into the structure of SO₄²⁻/TiO₂ seems to enhance the photocatalytic activity of the samples, which is ascribed to the enlargement of specific surface area, photogenerated carriers separation, light absorption, as well as the higher surface acidity.     

Growth of transition metal oxide crystals by halide vapour hydrolysis

Single crystals of NiO, CoO, FeO, Co₃O₄, and Fe₃O₄ have been epitaxially deposited on MgO single-crystal substrates by the hydrolysis of anhydrous metal bromides in the gaseous phase. All of the crystals were grown at temperatures below 700° C and at a total pressure of less than 25 torr. The deposition was usually complete after approximately 30 min, and the crystals were of uniform thickness with a glassy-clear, smooth surface. Depending on the number of depositions, these crystals can be formed in various thicknesses ranging from approximately 5 m to 1 mm. The crystals were found to deposit in parallel alignment with the (100) cleavage plane of MgO. A substantial increase in chemical purity is observed, and only 10³ to 10⁵ dislocations/cm² were observed in all NiO crystals. A reaction mechanism is proposed which involves: (i) the formation of a hydroxybromide transport phase with fluid properties; (ii) adsorption of the transport phase on the MgO substrate; followed by (iii), the chemical disproportionation-crystallisation of the intermediate phase to the oriented, solid oxide phase.Also associated with the Department of Geochemistry and Mineralogy.     

Formulation and characterization of glass–ceramics based on Na2Ca2Si3O9–Ca5(PO4)3F–Mg2SiO4-system in relation to their biological activity

Glasses having a chemical composition based on combeite [Na₂Ca₂Si₃O₉]–fluoroapatite [Ca₅(PO₄)₃F] and forsterite [Mg₂SiO₄] system were crystallized through controlled heat-treatment. Two forms of sodium calcium silicate e.g. combeite Na₂Ca₂Si₃O₉ and pectolite Na₂CaSi₃O₈, were formed together with diopside (CaMgSi₂O₆) and monticellite (CaMgSiO₄) in addition to fluoroapatite (Ca₅(PO₄)₃F) phases by thermal treatment of the glasses. Selected glass–ceramics were exposed to a simulated body fluid solution (SBF) which is close to human plasma for 3 weeks. Energy dispersive X-ray analysis (EDX) and inductive coupled plasma (ICP) analysis confirmed the formation of an apatite layer which indicate bioactivity in the all crystallized sample. A decreasing of surface bioactivity with increasing Mg₂SiO₄/Na₂Ca₂Si₃O₉ replacement was observed as indicated by the decrease in the amount of apatite layer on the surface of the crystallized specimens. The Vicker’s microhardness of the studied glass–ceramic materials are between 5,047 and 6,781 MPa.     

Uptake of various cations by amorphous BaAl2Si2O8 prepared by solid-state reaction of kaolin with BaCO3

The uptake of various ions by amorphous and crystalline BaAl₂Si₂O₈ was investigated. The BaAl₂Si₂O₈ samples were prepared by solid-state reaction of kaolin ground with BaCO₃ for periods from 1 to 24 h followed by firing at temperatures of 800–1200 °C for 24 h. Uptake experiments were performed at room temperature (25 °C) using a solid/solution ratio of 0.1 g/50 ml, with a cation concentration of 10⁻³ M and reaction time of 24 h. The cations used for the uptake experiments were alkaline earth ions (Mg²⁺, Ca²⁺ and Sr²⁺) and transition metal ions (Ni²⁺, Co²⁺, Cu²⁺ and Zn²⁺). The uptake of alkaline earth ions was low in all the samples while the transition metal ion uptakes were higher in the amorphous BaAl₂Si₂O₈ sample than crystalline BaAl₂Si₂O₈ samples. The high uptake of transition metal ions by the amorphous sample was further enhanced by prolonging the grinding time. Since the amorphous sample appears from the ²⁹Si and ²⁷Al NMR spectra to have a similar local structure to crystalline hexacelsian (double-layered structure consisted of alternatively corner shared AlO₄ and SiO₄ tetrahedra), the uptake of transition metal ions is suggested to occur by release of interlayer Ba ions in the vicinity of edge sites with the adsorption of transition metal ions from the solution.     

Ionic conductivity and crystallographic data for Na2-xCa1-xAlxSiO4 and Na2-xCaSi1-xPxO4 carnegieite phases

Single crystals of Na₂CaSiO₄ prepared at 30 kbar and 1500°C are cubic with $\text{a}\text{= 22.456}\text{A}\text{?}$. The polycrystalline compositions Na_1.9Ca_0.9Al_0.1SiO₄ and Na_1.8CaSi_0.8P_0.2O₄ can also be indexed using $\text{a}\text{= 22.458}\text{and}\text{22.471}\text{A}\text{?}$, respectively. The Ca carnegieites Na₂CaSiO₄, Na_1.9Ca_0.9Al_0.1SiO₄, and Na_1.8CaSi_0.8P_0.2O₄ have Na ion conductivities of only 5?8 × 10^?6 (ω-cm)^?1 at 300°C.     

Crystal growth of Bi2Sr2CuO6 from flux system KCl-KF and its superconductivity

Single crystals of Bi₂Sr₂CuO₆ (BSCO) were grown from high-temperature solution using KCl-KF as flux. Differential thermal analysis (DTA) of the starting materials enabled an appropriate temperature programme to be introduced for crystal growth by spontaneous nucleation. By means of the improved thermogravimetric (TG) method, Bi₂Sr₂CuO₆ crystals were grown after determination of the crystallization temperature. A single crystal in the form of a thin rectangular platelet up to 6×4 mm² was obtained and was identified by X-ray powder pattern and by scanning electron microscopy (SEM). Analyses were performed by using high-resolution electron probe microanalysis (EPMA), which indicated that it is the nonstoichiometric compound Bi_2+xSr_2–xCuO₆. The superconducting properties are strongly dependent on the composition of Bi and Sr in the crystals and on heat treatment. The transition temperature of 7 K with 0.5 K width for as-grown crystals, has been obtained.     

Formation mechanism of calcium phosphate coating on micro-arc oxidized magnesium

A calcium phosphate coating was prepared on the surface of micro-arc oxidized magnesium by a chemical method. The microstructure evolution of the coating was characterized by X-ray diffraction, Fourier-transformed infrared spectroscopy and scanning electron microscopy. The results showed that Ca₁₀(PO₄)₆(OH)₂ (HA) was firstly formed on the surface of micro-arc oxidized magnesium, followed by flake-like CaHPO₄·2H₂O (DCPD). The solution pH and Ca²⁺ concentration had intense influence on the formation of calcium phosphate coating. Acidic Ca²⁺ enrichment solution was favourable for HA formation on the surface of micro-arc oxidized magnesium. High concentration of HPO₄²⁻ and low concentration of Ca²⁺ in acidic solution improved the formation of DCPD coating.     

Low temperature fabrication of spherical brushite granules by cement paste emulsion

Secondary protonated calcium phosphates such as brushite (CaHPO₄·2H₂O) or monetite (CaHPO₄) have a higher resorption potential in bone defects than sintered ceramics, e.g. tricalcium phosphate or hydroxyapatite. However, processing of these phosphates to monolithic blocks or granules is not possible by sintering due to thermal decomposition of protonated phosphates at higher temperatures. In this study a low temperature technique for the preparation of spherical brushite granules in a cement setting reaction is presented. These granules were synthesized by dispersing a calcium phosphate cement paste composed of β-tricalcium phosphate and monocalcium phosphate together with a surfactant to an oil/water emulsion. The reaction products were characterized regarding their size distribution, morphology, and phase composition. Clinically relevant granule sizes ranging from 200?μm to 1?mm were obtained, whereas generally smaller granules were received with higher oil viscosity, increasing temperature or higher powder to liquid ratios of the cement paste. The hardened granules were microporous with a specific surface area of 0.7?m²/g and consisted of plate-like brushite (>95?% according to XRD) crystals of 0.5–7?μm size. Furthermore it was shown that the granules may be also used for drug delivery applications. This was demonstrated by adsorption of vancomycin from an aqueous solution, where a load of 1.45–1.88?mg drug per g granules and an almost complete release within 2?h was obtained.     

Seeded growth of hydroxyapatite in simulated body fluid

The precipitation of calcium phosphates was investigated, in simulated body fluid (SBF), pH 7.40 and 37°C. The kinetics of the mineral phase forming in the SBF was measured using the constant supersaturation method. The approach provides a detailed investigation in the processes taking place in the SBF which is widely used for the study of biomineralization. The pH adjustment was done by a pH-stat instead of Tris-Buffer [Tris (hydroxymethyl) Aminomethane] to avoid the presence of organic soluble compounds. The stability of SBF was investigated and the stable supersaturated solutions were seeded. The technique of seeded precipitation was employed for the achievement of accurate and reproducible kinetics measurements. The crystal growth experiments in which SBF solutions of variable supersaturations were seeded with hydroxyapatite [Ca₅(PO₄)₃OH, HAP] crystals showed that the precipitation of calcium phosphates took place exclusively on specific active sites provided on the surface of the synthetic seed crystals. The crystal growth mechanism showed that the process was controlled by surface diffusion. The phase formed was HAP in the lattice of which CO₃²⁻ and Mg²⁺ ions were incorporated. SBF was the source of these ions. Moreover it was found that the less stable calcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) may form as a transient phase hydrolyzing rapidly into the more stable HAP. Morphological examination of the carbonated apatites formed in the SBF showed appreciable aggregation.