Raman and NMR study of bioactive Na2O–MgO–CaO–P2O5–SiO2 glasses

The results of a structural study combining NMR and Raman spectroscopy of several melt-derived glasses in the system Na₂O–MgO–CaO–P₂O₅–SiO₂ are presented. The Raman spectra show clear changes in the Si–O–Si vibrational modes (related to the bridging oxygen atoms, BO) and also verify the presence of non-bridging oxygen atoms (NBO), also named terminal oxygens. The intensity of the Si–O–NBO stretching mode depends on the cation concentration. It can be concluded from the NMR studies that the MgO-containing samples have orthophosphate units charge-compensated by Ca²⁺ and Mg²⁺. The silicate matrix also contains both types of two-valent cations and consists of Q² and Q¹ units. Similarly, the Na₂O-containing samples contain isolated orthophosphate units in a silicate matrix (Q² and Q³ units), both charge-compensated by mixed cations Ca²⁺ and Na⁺. These experimental data were compared with theoretical parameters given by the Stevels model, which is a suitable tool for understanding bioactive behavior of these glasses. Furthermore, results of the in vitro tests carried out in simulated body fluids are presented and compared with both Raman and NMR structural data.     

Excited state absorption and up-conversion luminescence of Ho3+ centres in 3CaO–Ga2O3–3GeO2 glass

3CaO–Ga₂O₃–3GeO₂ glass excited state absorption spectra-activated with Ho³⁺ (Ho₂O₃ – 0.7 wt% content) have been measured and analysed. Up-converted emission channels have been identified and the predicted up-converted emission bands have been registered under Ar ion laser (λ = 488 nm) excitation according to the excited state absorption data. A mechanism of up-converted transitions for Ho³⁺ centres in this prototype glass network is proposed on the basis of the obtained results.     

Photosensitivity of SiO2–Al and SiO2–Na glasses under ArF (193 nm) laser

Photosensitivity of SiO₂–Al and SiO₂–Na glass samples was probed by means of the induced optical absorption and luminescence as well as by electron spin-resonance (ESR) after irradiation with excimer-laser photons (ArF, 193 nm). Permanent visible darkening in the case of SiO₂–Al and transient, life time about one hour, visible darkening in the case of SiO₂–Na was found under irradiation at 290 K. No darkening was observed at 80 K for either kind of material. This investigation is dedicated to revealing the electronic processes responsible for photosensitivity at 290 and 80 K. The photosensitivity of both materials is related to impurity defects excited directly in the case of SiO₂–Na and/or by recapture of self-trapped holes, which become mobile at high temperature in the case of SiO₂–Al. Electrons remain trapped on the localized states formed by oxygen deficient defects.     

Luminescence and energy transfer in Dy3+/Tb3+ co-doped CaO–Al2O3–B2O3–RE2O3 glass

The new calcium aluminoborate glasses with the composition of CaO–Al₂O₃–B₂O₃–RE₂O₃ (RE = Dy and Tb) were synthesized and the luminescence of Dy³⁺ and Tb³⁺ was investigated. The results show that the emission intensity of Tb³⁺ ion was enhanced when introducing Dy³⁺ ion into CaO–Al₂O₃–B₂O₃–Tb₂O₃ glass due to the energy transfer processes between Dy³⁺ and Tb³⁺. The energy transfer efficiencies, transfer probabilities as well as donor–acceptor critical distances were also calculated. The energy transfer mechanism between Dy³⁺ and Tb³⁺ ions is electric dipole–dipole interaction, which can be concluded by both fluorescence decay and emission intensity ratio varieties.     

Spectral investigations on VO2+ ion doped in CaO–SrO–Na2O–B2O3 glass systems

Glasses of the (20 ? x)CaO–xSrO–(20 ? y)Na₂O–60B₂O₃ ? y (CSNB) system with (5 ≤ x ≤ 15) mol% and y = 0.1 mol% of V₂O₅ were characterized by X-ray diffraction (XRD), EPR (Electron Paramagnetic Resonance), Optical absorption Spectra and FT-IR (Fourier transform Infrared Spectroscopy) studies. EPR spectra of all the glass samples exhibit resonance signals characterstic of VO²⁺ ions. The values of spin-Hamiltonian parameters indicate that the VO²⁺ ions in CSNB glasses were present in octahedral sites with tetragonal compression and belong to C_4v symmetry. Spin-Hamiltonian parameters ‘g’ and ‘A’ were evaluated. The Optical band energy (E_opt) and Urbach energy (ΔE) were calculated from their ultra violet edges. By correlating EPR and Optical data the molecular orbital coefficients have been evaluated. IR spectra of these glasses were analyzed in order to identify the contribution of each component to the local structure that determines the physical properties of these glasses.     

The preparation and structural studies in the (80 − x)TeO2–20ZnO–(x)Er2O3 glass system

Er³⁺-doped tellurite glasses of the (80 ? x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ? x ? 2.5 mol%) have successfully been made by melt-quenching technique and their structure has been investigated by means of DTA and Raman spectroscopy. The DTA results show the thermal parameters; such as the glass transition temperature (T_g) and crystallization temperature (T_c) were determined. It is found that this system provides a stable and wide glass formation range in which the glass stability around 99–140 °C may be obtained. The Raman spectroscopy used the structural studies in the glass system. Two Raman shift peaks were observed around 640–670 cm^?1 and 720–740 cm^?1, which correspond to the stretching vibration mode of TeO₄ tbp and TeO₃ tp, respectively. It is found that the spectral shift in Raman spectra is depending on the Er₂O₃ content. This evolution is an indication of the changes in the basic unit of the glass structure.     

Visible to near-infrared down-conversion luminescence in Tb3 + and Yb3 + co-doped lithium–lanthanum–aluminosilicate oxyfluoride glass and glass-ceramics

Tb^3 + and Yb^3 + co-doped oxyfluoride glasses were fabricated in a lithium–lanthanum–aluminosilicate matrix (LLAS) by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. Visible to near-infrared down-conversion luminescence was studied for glass and glass-ceramic samples with different Yb^3 + concentrations. It has been found that the luminescence intensity at 940–1020 nm from Yb^3 + ions increases while the emission lifetime of Tb^3 + ions decreases in the glass-ceramic compared to that in the as-prepared glass, which indicates that the energy transfer efficiency increases in the glass-ceramics compared to that in the as-prepared glass. The down-conversion luminescence also increased for increasing Yb^3 + concentration from 1 mol% to 2 mol%, but decreased for the sample with a high Yb^3 + co-doping concentration of 8 mol%, which is attributed to the concentration quenching.     

Synthesis and bioactive properties of macroporous nanoscale SiO2–CaO–P2O5 bioactive glass

A macroporous nanoscale bulk bioactive glass (SiO₂–CaO–P₂O₅ system) was prepared by sol–gel co-template method. Porosimeter analysis showed that the as-synthesized bioactive glasses (BGs) had a porosity of 85% and exhibited a multimodal pore size distribution, nanopores (10–40 nm) and macropores (100 nm–10 μm). Morphological and structural characterizations showed the pores were interconnected with pore walls of about 250 nm in width and 1 μm in length. In vitro bioactivity test indicated that the as-synthesized bulk BGs exhibited faster apatite layer formation capability than the conventional sol–gel BGs. Additionally, the deposited layer was identified as hydroxycarbonate apatite, which is similar to the inorganic part of human bone.     

Characteristics and biocompatibility of Na2O–K2O–CaO–MgO–SrO–B2O3–P2O5 borophosphate glass fibers

A novel Na₂O–K₂O–CaO–MgO–SrO–B₂O₃–P₂O₅ borophosphate glass fiber is prepared. The thermal properties including differential thermal analysis (DTA) and viscosity measurement of the glass were presented. The tensile strength of the glass fiber is measured. The reaction of the glass fibers in the SBF solution is characterized by XRD, FTIR and SEM. XRD and FTIR indicate that the carbonate hydroxyapatite has formed rapidly on the glass. Cell attachment, spreading and proliferation on the glass are determined by MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay method using Human osteosarcoma MG-63 cells. The bioactivity and biocompatibility of the glass fiber make it a good potential prospect in the field of tissue engineering.     

Local structure around phosphorus and silicon in the CaO–SiO2–PO2.5 system

The local structure of phosphorus and silicon in the molten CaO–SiO₂–PO_2.5 slag system was investigated by magic angle spinning nuclear magnetic resonance (MAS-NMR). The ³¹P MAS-NMR spectra revealed that phosphorus was present primarily as the monophosphate complex ion PO₄^3?, with a small amount of diphosphate ion also present. Their relative ratio to total phosphorus was independent of the phosphate concentration of the sample. In the case of the ²⁹Si MAS-NMR, the mean number of the non-bridging oxygen atoms associated with tetrahedrally coordinated silicon decreased as the phosphate concentration increased at a fixed CaO/SiO₂ ratio. This indicates that the nonbridging oxygen atoms around the silicon were replaced by bridging oxygen atoms around the phosphorus as the phosphate concentration in the samples increased.To elucidate the basicity dependence of the structure of slag, the relationship between the structure and optical basicity was also investigated. The relative ratio of Qⁿ (Qⁿ means the silicon atoms tetrahedrally bonded with “n” number of bridging oxygen atoms) strongly depends on the optical basicity. These optical basicity dependencies of the structures of phosphorus and silicon can be explained clearly by the basicity equalization concept (Duffy and Ingram, 1976) [12].     

Crystallization behavior and microstructure of (CaO·ZrO2·SiO2)–Cr2O3 based glasses

The effects of chromium oxide on the crystallization behavior of glass compositions in the calcium, zirconium and silicon oxides system were investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopic. Results indicate that crystallization is predominantly controlled by a surface nucleation mechanism, even though a partial bulk nucleation has been encountered in compositions containing more than 1.0 mol% of doping oxide. The effect of heating rate on differential thermal analysis curves was studied in order to investigate nucleation mechanisms and to extract the corresponding crystal growth activation energies E_c for the different crystalline phases. Activation energy (E_c) was found to be 490 ± 5 kJ/mol for 5.0 mol% chromium oxide in glasses. The most suitable nucleation temperature was determined as 810 °C for the above mentioned glass. The results of this study have highlighted that a small percentage of chromium oxide strongly affects the crystal formation thereby reducing the time and temperature of the thermal treatment and enhancing the degree of crystallization of calcium, zirconium and silicon oxides glasses.     

Structure and properties of the 70Li2S · (30 − x)P2S5 · xP2O5 oxysulfide glasses and glass–ceramics

The 70Li₂S · (30 ? x)P₂S₅ · xP₂O₅ (mol%) oxysulfide glasses were prepared by the melt quenching method. The glasses were prepared in the composition range 0 ≦ x ≦ 10. The glass–ceramics were prepared by heating the glasses over crystallization temperatures. The PO_nS_3?n (n = 1–3) oxysulfide units were produced in the glasses and glass–ceramics by partial substituting P₂O₅ for P₂S₅. In particular, the P₂OS₆^4? unit would be produced by substituting a small amount of P₂O₅ for P₂S₅. The oxygen atoms were incorporated into the Li₇P₃S₁₁ crystal structure because the diffraction peaks of the oxysulfide glass–ceramic shifted to the higher angle side. The glass–ceramic with 3 mol% of P₂O₅ exhibited the highest conductivity of 3.0 × 10^?3 S cm^?1 and the lowest activation energy for conduction of 16 kJ mol^?1. The P₂OS₆^4? dimer units in the oxygen-incorporated Li₇P₃S₁₁ crystal would improve conductive behavior of the Li₂S–P₂S₅ glass–ceramics.     

Synthesis and structure–property relations in xCuO–(1 − x)Bi2O3 (0.5 ⩽ x ⩽ 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses

Synthesis of the xCuO–(1 ? x)Bi₂O₃ (0.5 ? x ? 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses was done via nitrate–citrate gel route. Glassy phase is ascertained by XRD studies. Magnetic susceptibility results in the range 4.2–400 K show weak paramagnetic nature with exchange integrals ～0.024–0.13 eV in the glasses. The electron paramagnetic resonance (EPR) in the range 4.2–363 K shows g ≈ 2.0 and the trend of the g-matrix elements g_|| > g_⊥ > g_e for the glasses C1–C5 at 4.2 K are due to the Cu²⁺ (3d⁹) paramagnetic site in the glasses which is in a tetragonally elongated octahedron [O_1/2–CuO_4/2–O_1/2] having D_4h symmetry. IR spectroscopic results show the presence of octahedron [BiO_6/2]^3? and [CuO_6/2]^4? units and pyramidal [BiO_2/2O]^? unit in the glasses.     

Sol–gel synthesis and characterization of unexpected rod-like crystal fibers based on SiO2–(1-x)CaO–xSrO–P2O5 dried-gel

Sol–gel technique has several benefits for the preparation of glass, and morphology can be better controlled compared to conventional methods. In this research, new sol–gel derived bioactive glasses based on SiO₂–CaO–SrO–P₂O₅ dried-gel were synthesized and characterized. Herein, a series of 58S bioactive glasses with the composition of 60%SiO₂–36%(CaO/SrO)–4%P₂O₅ (mol%) were synthesized, and the effect of adding strontium (Sr) to the glass structure SiO₂–(1-x)CaO–xSrO–P₂O₅ (where x = 0, 0.5, 0.1, 0.25, 0.5 and 1) was investigated by gradually substitution of Sr with calcium (Ca). The obtained results indicated that the Sr free sample totally takes amorphous state indicative of the internal disorder, glassy nature and non-crystalline states of this material. Surprisingly, after further addition of Sr to the glass structure, the X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) micrographs showed unexpected significant rod-like crystal fibers, and the major diffraction peaks of Sr(NO₃)₂, SrCO₃ and Sr₂Si₂O₄ became sharper and more apparent up to the final addition of Sr. The complicated and contradictory results underscore the need for better knowledge of how impurities act upon by growing rod-like crystals. In addition, totally understanding the effect of Sr on the morphology of samples from the bottom up is a daunting challenge.     

Growth of Sm1 – ySryF3 – y (0 < y ≤ 0.31) Crystals and Investigation of Their Properties

Crystallography Reports - Sm1&nbsp;–&nbsp;ySryF3&nbsp;–&nbsp;y (0 &lt; y ≤ 0.31) crystals have been grown from melt by directional solidification in a...     

Micro-structural studies of GeSe2–Ga2Se3–MX (MX = CsI and PbI2) glasses using Raman spectra

Microstructure of the chalcohalide glasses: GeSe₂–Ga₂Se₃–CsI and GeSe₂–Ga₂Se₃–PbI₂ ternary system were investigated by Raman spectra, lifetime of Dy³⁺ infrared emission and glass transition temperature (T_g). The evolution of the Raman spectra shows that the fundamental structural groups of these studied glasses consist of [Ge(Ga)Se₄] tetrahedral and some complex structure units [Ge(Ga)I_xSe_4?x](x = 1–4). The x value varied when the different iodide was added in Ge–Ga–Se matrix. For GeSe₂–Ga₂Se₃–CsI glasses, the [Ge(Ga)I_xSe_4?x](x = 1–4) mixed-anion tetrahedral and [Ga₂I₇]^? units occurred. For GeSe₂–Ga₂Se₃–PbI₂ glasses, the [Ge(Ga)I₂Se₂], [Ge(Ga)I₃Se] units can be formed. The changes of Dy³⁺ infrared emission lifetime and T_g support the results. Additionally, [PbI_n] structural units will be formed in GeSe₂–Ga₂Se₃–PbI₂ glasses due to high form-ability of these units when the PbI₂ content is high.     

Nanostructured Crystals of Fluorite Phases Sr1 – xRxF2 + x (R Are Rare-Earth Elements) and Their Ordering. 15. Concentration Dependence of the Defect Structure of As Grown Nonstoichiometric Phases Sr1 – xRxF2 + x (R = Sm,Gd)

Crystallography Reports - The defect structure of as grown single crystals Sr1&nbsp;–&nbsp;xSmxF2&nbsp;+&nbsp;x (x = 0.14, 0.26) and...     

Pr3 +–Yb3 +‐codoped lanthanum fluorozirconate glasses and waveguides for visible laser emission

Pr^3 +–Yb^3 +‐codoped fluoride glass waveguides have been synthesized by Physical Vapor Deposition (PVD). A study of the evaporation of ternary mixture of rare earth fluorides LaF₃–PrF₃–YbF₃ has been necessary to control the doping of the evaporated glass. Optical and spectroscopic studies have been performed in both bulk and waveguide configuration. Red, orange, green and blue emissions in Pr^3 +–Yb^3 +-codoped lanthanum flurozirconate glasses called ZLAG have been investigated, by exciting in the blue or in the infra-red at 980 nm. Bulk samples with different dopant concentrations (0.25–3 mol% for Pr^3 + and 0–5 mol% for Yb^3 +) have been studied in order to optimize the Pr^3 + emission. It has been shown than the luminescence is similar in bulk and waveguide upon excitation at 980 nm.