Phosphate Glass-ceramics Research Articles

(Invited) Thermal Quenching of Phosphors: How to Reduce/Remove It?

The most significant revolution in artificial lighting is prompted by the work of 2014 Nobel laureates who developed efficient blue light-emitting diodes enabling bright and energy saving phosphor-converted white light-emitting diodes (pc-WLEDs). However, the most critical property is the thermal stability of phosphors, since, in general, emission losses occur during LED operation due to heat generation (~200˚C), which is detrimental to pc-WLEDs and this process is known as thermal quenching (TQ). In this talk, different techniques have been employed to enhance the thermal stability of phosphor, such as making solid-solution of phosphors, applying ceramic coatings onto phosphor surfaces, and glass ceramic phosphor. Also we report the first of the self-healing blue phosphor that does not exhibit TQ, and sustains its emission intensity up to 200°C.

Microwave Crystallization of Lithium Aluminum Germanium Phosphate Solid-State Electrolyte.

Lithium aluminum germanium phosphate (LAGP) glass-ceramics are considered as promising solid-state electrolytes for Li-ion batteries. LAGP glass was prepared via the regular conventional melt-quenching method. Thermal, chemical analyses and X-ray diffraction (XRD) were performed to characterize the prepared glass. The crystallization of the prepared LAGP glass was done using conventional heating and high frequency microwave (MW) processing. Thirty GHz microwave (MW) processing setup were used to convert the prepared LAGP glass into glass-ceramics and compared with the conventionally crystallized LAGP glass-ceramics that were heat-treated in an electric conventional furnace. The ionic conductivities of the LAGP samples obtained from the two different routes were measured using impedance spectroscopy. These samples were also characterized using XRD and scanning electron microscopy (SEM). Microwave processing was successfully used to crystallize LAGP glass into glass-ceramic without the aid of susceptors. The MW treated sample showed higher total, grains and grain boundary ionic conductivities values, lower activation energy and relatively larger-grained microstructure with less porosity compared to the corresponding conventionally treated sample at the same optimized heat-treatment conditions. The enhanced total, grains and grain boundary ionic conductivities values along with the reduced activation energy that were observed in the MW treated sample was considered as an experimental evidence for the existence of the microwave effect in LAGP crystallization process. MW processing is a promising candidate technology for the production of solid-state electrolytes for Li-ion battery.

Thermal and ionic conductivity studies of lithium aluminum germanium phosphate solid-state electrolyte

Two different compositions of lithium aluminum germanium phosphate glass–ceramics (LAGP) were prepared and investigated as candidate materials for solid-state electrolytes in Li-ion batteries. The thermal and the ionic conductivity behavior of these two different LAGP compositions were investigated. LAGP glasses were prepared using the melt-quench-method. Glass–ceramic samples were obtained from the prepared glasses via two different methods: powder sintering and bulk glass heat-treatment. The ionic conductivity was measured using complex impedance spectroscopy while the thermal diffusivity was measured using a Laser flash apparatus. The thermo-physical properties were studied using differential scanning calorimetry. X-ray diffraction and scanning electron microscopy were used to investigate the crystal structure and the microstructure. The sample with higher ionic conductivity had also shown higher thermal conductivity in the two different studied LAGP compositions. Moreover, the thermal conductivity was depending on the microstructure and density of the samples. Finally, the temperature dependence of the thermal conductivity could not be explained by a single mechanism or by the Wiedemann–Franz law. Therefore, a contribution of the mobile ions to the thermal transport might probably occur.

Yb3+/Tb3+ co-doped GdPO4 transparent magnetic glass-ceramics for spectral conversion

Tb3+ and Yb3+ ions co-doped transparent phosphate glass-ceramics containing monoclinic GdPO4 nanocrystals were successfully synthesized using a conventional high temperature melting quenching method in air atmosphere. The structure and morphology properties were systematically analyzed by recording X-ray diffraction patterns and transmission electron microscopy images, which indicate the GdPO4 glass-ceramics was well formed. The luminescent properties of the GdPO4: Yb3+, Tb3+ were investigated based on excitation, emission spectra and decay curves. All samples exhibited the emission of Tb3+ ions from 5D4 → 7FJ (J = 6, 5, 4 and 3) and 5D3 → 7FJ (J = 6, 5 and 4) under irradiation with ultraviolet and near infrared light. Specially, strong green up-conversion emission of Tb3+ at 543 nm (5D4 → 7F5) is observed. And the decay curves illustrate more efficient UC process in GdPO4 glass-ceramics rather than precursor glass. Energy transfer from Gd3+ to Tb3+ as well as cooperative energy transfer from Yb3+ pair to Tb3+ gives a dual mode luminescence. Laser power dependence of up-conversion shows that two-photon process is responsible for the green emission as expected. Additionally, the paramagnetic property of this material was discussed. The hysteresis plot (M−H) analysis results at room temperature indicate their good paramagnetic property. Based on the above results, the block GdPO4 glass-ceramics have potentials to serve as multifunctional materials applied in laser field materials.

Role of titanium ions on the physical and structural properties of calcium zinc bismuth phosphate glass ceramics

The transparent glass ceramics of composition 10CaF2–20ZnO–(15–x)Bi2O3–55P2O5: xTiO2 (0≤x≤4) were prepared by melt quenching followed by heat treatment. The prepared samples were characterized by X-ray diffraction, differential thermal analysis and scanning electron microscopy. These studies have revealed that the samples contain well defined randomly distributed crystalline phases with the complexes of Ti4+ and Ti3+ ions. Spectroscopic studies viz., optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman were also carried out on these glass ceramics. The results of optical absorption and electron paramagnetic resonance studies revealed that part of the titanium ions exist in Ti3+ state that occupy the tetragonally distorted octahedral sites in the glass ceramic network and these ions are found to increase with an increase in the content of nucleating agent TiO2. Fourier transform infrared and Raman studies indicating the formation of TiO6 structural units along with cross linkages viz., P–O–Bi, P–O–Ti. But when TiO2 is present in the larger quantities, the Π-bond of P=O may be ruptured by TiO4 structural units which may cause the creation of new non-bridging oxygen ions facilitating the formation of [TiO6/2]2− structural units also. Therefore, the analysis of spectroscopic studies indicating that the glass ceramics contain greater than 2mol% of TiO2 is suitable for semiconducting applications.

Wollastonite - Tricalcium Phosphate Glass-Ceramics of Eutectic Composition Synthesized by the Glass-Crystallization Method

ABSTRACTGlass-ceramics of eutectic composition in the wollastonite [W, CaO⋅SiO2]- tricalcium phosphate [TCP, β-Ca3(PO4)2] binary system were synthesized by using the glass-crystallization method. The parent glass was crystalized at 800-1300 °C for 0.5-5 h. The in vitro bioactivity of the synthesized glass-ceramics was tested in Kokubo’s Simulated Body Fluid (SBF) for 7-21 days, at pH = 7.4 and 37 °C. All materials were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS). The results showed that metastable Apatite phase [Ap, Ca10(PO4)6O], plus W and TCP phases expected according to the binary phase diagram, were formed. Ap was the first phase formed at 900 °C/0.5 h, which was followed by formation of W phase at 900 °C/2 h and of TCP phase at 1200 °C/0.5 h. The relative proportion of the formed crystalline phases was a function of heat treatment temperature and time. A eutectic microstructure was obtained for the materials heat-treated at 1300 °C for 2 or 5 h. All glass-ceramics showed the formation of a hydroxyapatite (HAp)-like layer during the in vitro bioactivity tests. After 21 days of soaking in SBF, the samples treated at 1300 °C/5 h showed a behavior similar to that typically shown by Bioeutectic® material, while the materials heat-treated at lower temperatures tended to form denser HAp-like layers, with similar thicknesses but with higher Ca/P molar ratios.

Crystallization and sintering behaviors of the polyphosphate glass doped with Zn and Mn

The crystallization and sintering behaviors of polyphosphate glass doped with trace elements Zn and Mn were examined. The heating experiments on bulk and powder glass samples were performed. The parent glass revealed low crystallization ability and the glass crystallization carried out under simultaneous acting of the surface and volume mechanisms. The bulk glass sample isothermally heated at Tc = 500 °C commences to crystallize after 12 h, and KPO3 and Ca2KP3O10 crystalline phases appeared. The dendritic morphology of the crystals growing on sample surface was determined. The DTA and HSM results showed that the sintering and crystallization processes are independent. Phosphate glass-ceramics containing KPO3, K2Mg(PO3)4, Ca(PO3)2 and KCa(PO3)3 crystalline phases has been prepared by sintering of the glass powder compacts at Tc = 500 °C for t = 12 h. A plate-like morphology of crystals which grow on glass grains surface was observed. The activation energies of crystal growth, Ea,k = (246.6 ± 19.74) kJ mol−1 (Kissinger) and Ea,oz = (258.80 ± 19.70) kJ mol−1 (Ozawa), were calculated.

Red and Green Phosphors Glow on the Basis of Oxide Glass-Ceramics Doped with Eu<sup>3+</sup> and Tb<sup>3+</sup>

Glass-ceramics phosphors were obtained by the introduction of the crystalline phase NaMg3Sc (MoO4)5:Eu3+,Tb3+ in the glass composition 8SiO2-20B2O3-5Lu2O3-31Bi2O3-36ZnO. The properties were characterized by X-ray diffraction (XRD), photoluminescence (PL) and photoluminescent excitation spectra (PLE). The XRD patterns were indicated NaMg3Sc (MoO4)5:Eu3+,Tb3+ crystallize well with the novel structure type and were assigned to the triclinic phase (space group PĪ, Z = 6). Glass-ceramic phosphors are well-known and promising as solid electrolytes, laser, luminescent and other inorganic materials. Luminescent properties of the phosphors are performed at room temperature. The excitation spectra of Eu-doped phosphor present strong absorption at 300 nm and the sharp peaks in the 350-500 nm range. Under the 394 nm excitation, intense red emission peak at 616 nm corresponding to 5D0→7F2 transition of Eu3+ is observed in the emission spectrum. The luminescence property indicates that the local symmetry of Eu3+ ion has no inversion center. The excitation spectra of Tb-doped phosphor by monitoring wavelength at 546 nm shows the intense broad band from 260 to 420 nm and the line at 234 nm, which is mainly attributed to charge-transfer band transition in MoO42- group, indicating the existence of energy transfer from MoO42- to Tb3+ in the Tb3+:glass-ceramic. The measured emission spectrum of Tb-doped phosphor has intense green emission at 546 nm corresponding to 5D4→7F5 transition of Tb3+, with λex=368 nm. The as-prepared phosphors may find potential applications in the field such as color displays, light-emitting diodes (LEDs) and optoelectronic devices.

Tm3+/Tb3+/Sm3+ tri-doped transparent glass ceramic for enhanced white-light-emitting material

The luminescent properties of the Tm3+/Tb3+/Sm3+ ions in phosphate glasses and glass ceramics have been investigated for the generation of white light. The X-ray diffraction pattern of the glass ceramics reveals the presence of SrZnP2O7 nano-crystals in the glass matrix after a suitable thermal treatment of the parent glasses. Bright white light emission of the glass and glass ceramic samples has been observed when the samples are excited with 357 nm light. Significantly increased luminescent intensity is observed from glasses to glass ceramics.

Alkali-free bioactive diopside–tricalcium phosphate glass-ceramics for scaffold fabrication: Sintering and crystallization behaviours

The sintering and crystallization behaviours of alkali-free bioactive glass compositions designed in the diopside (CaO·MgO·2SiO2)–tri-calcium phosphate (3CaO·P2O5) binary join by varying the Di/TCP ratios were investigated by hot-stage microscopy and differential thermal analysis, respectively. The effects of non-isothermal heating for 1h at 900, 1000 and 1200°C on the structural changes were assessed by solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) and crystalline phase assemblage. The influence of the heat treatment temperature on 3 point bending strength was also investigated. Diopside and hydroxyapatite formed as primary crystalline phases, accompanied by calcium silicate as secondary phase, in samples are sintered at 900°C and 1000°C. With further increase of the heat treatment temperature to 1200°C, whitlockite that was stated appearing in some compositions at 1000°C, appeared as main crystalline phase after diopside as a result of hydroxyapatite transformation. The data gathered was highly relevant towards setting the experimental conditions required for preparing well sintered and mechanically strong glass/glass-ceramic scaffolds for bone regeneration and tissue engineering applications.

The biological properties of the silver- and copper-doped ceramic biomaterial

The biological properties of nanostructured bioactive ceramic composite (BCC) granules doped with 0.1–10 at.% silver and 0.05–5 at.% copper have been investigated both in vitro and in vivo to develop effective alloplastic material for infected bone defect substitute. It is assumed that the granules consisting of biphasic calcium phosphate and bioactive glass ceramics due to their nanoscale (15–40 nm) and multiphase structure, bioelement placement in different ceramic phases as well as antimicrobial effect should improve osteogenic properties and biocompatibility. Tests in vitro have been conducted with multipotent mesenchymal stromal cells (MSCs) and test strains of microorganisms. The same biocomposite has been used in vivo to study the repair of bone defects in animal model. The findings indicate that doped BCC leads to antimicrobial activity. Inhibition of MSCs growth has been observed for granules doped with ions of more than 1 at.% silver and 0.5 at.% copper. The results of the in vivo study reveal that BCC implantation significantly improves bone reparation. Differences between bone repair with undoped and doped, with 1 at.% silver and 0.5 at.% copper, ceramic samples were not observed. The BCC doped within 0.5–1 at.% silver and 0.25–0.5 at.% copper stimulates bone tissue repair and has satisfactory biocompatibility and antimicrobial properties.

Iron Phosphate Glass-ceramics

Iron Phosphate Glass-ceramics

FTIR spectral analysis and mechanical properties of sodium phosphate glass–ceramics

Glasses of compositions xNa2O–(100−x)P2O5, (40⩽x⩽55) were prepared by melt-quench technique. Controlled heat treatments of these glasses were done to obtain the glass–ceramics. Density of glass–ceramics increases with increasing content of Na2O. X-ray diffraction pattern exhibited two crystalline phases, i.e., NaPO3 and Na2H2P2O7 in all the glass–ceramic samples. FT-IR and Raman study revealed the de-polymerization of phosphate groups, that changes Q2→Q1→Q0 with Na2O content and heat treatment. The scanning electron microscope study confirmed that interlocked crystals are dispersed in a glassy matrix. The Young’s moduli of glass–ceramics are observed in the range of (17.3–21.5)GPa with the increase of Na2O content. The highest value of micro-hardness observed is 918MPa in x=55mol% Na2O glass–ceramic sample. The observed elastic moduli of glass–ceramics are comparable to the other solid electrolyte which is being used in Na-ion batteries.

Influence of lead and cadmium fluoride variation on white light emission characteristics in oxyfluoride glasses and glass–ceramics

The radiative properties of Dy-doped glasses and glass–ceramic phosphors with varying lead and cadmium fluoride content are investigated in the present study for white light emitting applications. The precipitation of cubic lead fluoride phase of 10–18nm crystallites was determined with the help of x-ray diffraction studies and the nanocrystalline nature was confirmed with scanning electron microscopy studies. The small size of the nanocrystallites enables the fabrication of transparent glass–ceramics which is verified by UV–vis spectroscopic study. The photoluminescence and lifetime measurements indicate towards progressive changes in the Dy3+ ion surroundings and propose enhanced energy transfers taking place post-heat treatments. Finally, CIE chromaticity coordinates are found to lie in the white region proposing the suitability of the present studied materials for color display devices.

Advances in transparent glass–ceramic phosphors for white light-emitting diodes—A review

Abstract Currently, the major commercial white light-emitting diode is the phosphor converted LED made of blue-emitting chip and Y 3 Al 5 O 12 :Ce 3+ yellow phosphor dispersed in organic silicone. However, the organic binder in high-power device ages easily and turns yellow due to accumulated heat emitted from chip, which adversely affects the device properties such as luminous efficacy and color coordination, and therefore reduces its long-term reliability as well as lifetime. In this mini-review article, we provide an overview of recent progresses in developing transparent inorganic glass–ceramics phosphors excitable by blue chip, as an alternative to conventional polymer-based phosphor converter, for construction of high-power white light-emitting diodes. Two kinds of synthesis routes, glass crystallization and low-temperature co-sintering, are discussed in detail. Afterwards, the materials design, structure/property optimization as well as glass–ceramic-based WLED devices construction are summarized. Finally, challenges and future advances for the realization of transparent glass–ceramics in commercial applications will be presented.

KrF excimer laser precision machining of hard and brittle ceramic biomaterials

KrF excimer laser precision machining of porous hard–brittle ceramic biomaterials was studied to find a suitable way of machining the materials into various desired shapes and sizes without distorting their intrinsic structure and porosity. Calcium phosphate glass ceramics (CPGs) and hydroxyapatite (HA) were chosen for the study. It was found that KrF excimer laser can cut both CPGs and HA with high efficiency and precision. The ablation rates of CPGs and HA are respectively 0.081 µm/(pulse ⋅ J cm−2) and 0.048 µm/(pulse ⋅ J cm−2), while their threshold fluences are individually 0.72 and 1.5 J cm−2. The cutting quality (smoothness of the cut surface) is a function of laser repetition rate and cutting speed. The higher the repetition rate and lower the cutting speed, the better the cutting quality. A comparison between the cross sections of CPGs and HA cut using the excimer laser and using a conventional diamond cutting blade indicates that those cut by the excimer laser could retain their intrinsic porosity and geometry without distortion. In contrast, those cut by conventional machining had distorted geometry and most of their surface porosities were lost. Therefore, when cutting hard–brittle ceramic biomaterials to prepare scaffold and implant or when sectioning them for porosity evaluation, it is better to choose KrF excimer laser machining.

Porous hydroxyapatite scaffolds containing calcium phosphate glass-ceramics processed using a freeze/gel-casting technique

A freeze/gel-casting technique has been applied to produce porous ceramic composite scaffolds with tailored pore structures and improved compressive strength for tissue engineering applications. Tertiary-butyl alcohol (TBA)-based hydroxyapatite/calcium phosphate glass-ceramic suspensions with 5–15 vol.% solid loading were used in this study. Following sintering at 1050–1250 °C, the composite scaffolds were characterized in terms of microstructure, and physical and mechanical properties. The resulting scaffolds consisted of unidirectional pore channels (macro-sized) aligned in the solidification direction of the TBA solvent used in the freeze casting step and a few inter/intra-granular pores with small diameter (micron sized) remained in the wall structures of the pore channels by gel casting. With the addition of glass-ceramics (≤10 wt%), a liquid phase was formed mainly by the melting of calcium phosphate glasses at a given sintering temperature. The wall structures became more densified (less porous) aided by liquid phase sintering, possibly lending enhanced compressive strength.

Influence of thermal treatment on the structure and in vitro bioactivity of sol-gel prepared CaO-SiO2-P2O5 glass-ceramics

Nowadays there is a substantial practical interest in the in vitro bioactivity of calcium silicate phosphate (CSP) glass-ceramics and carbonate apatite (CO3HA) formation on their surfaces after in vitro test in simulated body fluid (SBF). The main purpose of the presented article is the evaluation of the chemical composition of the gel with nominal composition 70.59 CaO:28.23 SiO2:1.18 P2O5 (mol.%) on the structure, crystallization behaviour and in vitro bioactivity in SBF solution for 14 and 28 days. The prepared glass-ceramics have been synthesized via a polystep sol-gel method. The structure of the obtaining samples was studied by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). After thermal treatment of the samples XRD confirmed the presence of ?-Ca2SiO4 and Ca15(PO4)2(SiO4)6, and indicated that at 1500?C Ca15(PO4)2(SiO4)6 becomes predominant phase. FTIR revealed the presence of all characteristics bands for calcium silicate phosphate (CSP) bonds. SEM monitors the presence of particles with different morphology. After in vitro test in SBF, FTIR depicted that B-type carbonate containing hydroxyapatite (CO3HA) is preferentially formed on the immersed glass-ceramics. SEMof the precipitated layers showed the presence of HA spheres. The changes in SBF solution after soaking the samples were recorded by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

Thermal and structural study of glasses in the binary system TeO2–Pb(PO3)2

The main objective of this work has been to prepare and characterize the thermal and structural properties of glasses in the pseudo binary system TeO2–Pb(PO3)2 with respect to the composition. Homogeneous and transparent glass samples were obtained by the melt-quenching method in a large glass forming range in the pseudo binary system (100−x)TeO2–xPb(PO3)2 with x varying from 5 to 100. Thermal properties investigated by DSC pointed out an increase of the glass transition temperature from x=5 to x=40 and further decrease of Tg for higher Pb(PO3)2 concentrations. A similar tendency has been observed for the thermal stability against devitrification measured using the stability parameter Tx–Tg. FTIR together with Raman spectroscopies allowed building a structural model for these glasses with the contribution of distinct phosphate and tellurite units depending on the composition. Identification of crystalline phases obtained after the glasses heat-treatments obtained by X-ray diffraction support the structural evolution suggested by vibrational spectroscopies. These data suggest that incorporation of TeO2 in the lead metaphosphate glass results in tellurium conversion from TeO4 seesaw geometry to TeO3 trigonal pyramids and consequent conversion of well-known metaphosphate units Q2 to modified pyrophosphate units Q21Te in which the phosphorus PO4 tetrahedron is linked to another PO4 unit and one TeO3 pyramid. These tellurite trigonal units cross-link the modified metaphosphate chains with a resulting increase of the glass network connectivity. For high TeO2 concentrations, all Q2 were converted to Q21Te and the additional tellurium atoms are incorporated in the glass network as TeO4 seesaw units with a glass network built from a tridimensional network of TeO3, TeO4 and Q21Te. Finally, this work pointed out the possibility to use this pseudo-binary system for the preparation of phosphate glass-ceramics containing a TeO2 crystalline phase or tellurite glass-ceramics containing a pyrophosphate or metaphosphate crystalline phase.

Optical Investigations in Er<sup>3+</sup>/Yb<sup>3+</sup> Co-Doped Nanostructured Phosphate Glass Ceramics

Er3+/Yb3+co-doped transparent phosphate glass ceramics were fabricated and characterized optically. The formation of nanocrystals is confirmed by x-ray diffraction. Stark split near infrared emission peaks of Er3+have been observed in the glass ceramics, and the effective bandwidth increases with increasing annealing temperature. Upconversion emissions of Er3+in the glass ceramics under 975nm wavelength excitation, especially in the green wavelength region, are enhanced. The results can be attributed to the enhancement of ligand field due to incorporation of Er3+ions into the crystal lattices.