Phosphate Glass-ceramics Research Articles

The structural role of manganese ions in some zinc phosphate glasses and glass ceramics

X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy measurements have been employed to investigate the samples from the (MnO) x ·(P 2O 5) 40·(ZnO) 60− x (0 ≤ x ≤ 30 mol%) system. The samples had a fixed P 2O 5 content of 40 mol% and the MnO:ZnO ratio was varied. The XRD pattern for the prepared samples shows that the vitreous phase is present only for x ≤ 20 mol%. For the sample containing 30 mol% MnO the presence of a crystalline phase was evidenced, namely the manganese phosphate (Mn 2P 2O 7) embedded in an amorphous matrix. In this case the XRD patterns show the presence of nanometer crystals (56 nm) in a glassy matrix. The estimated amount of the crystalline phase was 74%. The electron micrographs show the structural evolution of the studied samples from a completely amorphous state (for the samples up to 20 mol% MnO) to a partly crystalline one (for the sample with 30 mol% MnO). FTIR data revealed that the short-range order of the glassy matrix is affected by the addition of the MnO to the (P 2O 5) 40·(ZnO) 60 host glass matrix. The compositional dependence of the different structural units which appear in the studied samples was followed. FTIR spectroscopy data suggest that the manganese ions play the network modifier role in the studied samples.

Development of glass ceramic phosphors for white LEDs

Development of glass ceramic phosphors for white LEDs

Influence of light scattering on luminous efficacy in Ce:YAG glass-ceramic phosphor

In Ce:YAG–GC, Ce 3+ ions, incorporated in the Y sites of the precipitated Ce:YAG micro crystals, emit yellow fluorescent light when they are optically excited by a blue LED. White light emission can be obtained by mixing the exciting blue light and the fluorescent yellow light. In the emission process of Ce:YAG– GC, light scattering generally occurs at the phase boundary between the precipitated Ce:YAG micro crystals and the glassmatrix phase due to the difference in refractive index. Since the light scattering changes the direction of both the exciting blue light and the fluorescent yellow light, this directly affects the luminous efficacy of Ce:YAG–GC phosphor. In this study, the interdependence between Ce:YAG particle si ze, luminous efficacy, and the light scattering coefficient were investigated in order to improve the luminous efficacy of Ce:YAG–GC phosphor. Since the luminous efficacy should be affected by the light scattering, as mentioned above, an understanding of light scattering phenomena is critical for the development of Ce:YAG–GC phosphor with higher luminous efficacy. 2. Experimental

Thermal Quenching of Ce3+:Y3Al5O12 Glass-Ceramic Phosphor

The thermal quenching of fluorescence of Ce:Y3Al5O12 glass-ceramic (YAG-GC) phosphor was evaluated and compared with those of Ce:Y3Al5O12 polycrystal (YAG-PC) and Ce:(Gd,Y)3Al5O12 glass-ceramic (GdYAG-GC). The fluorescence intensity of YAG-GC showed a lower temperature dependence than that of GdYAG-GC, although it showed a more marked decrease with increasing temperature than that of YAG-PC.

The luminescence properties of Er 3+-doped and Er 3+–Tm 3+-co-doped phosphate glasses for white light emitting diode

Phosphate glasses and glass ceramics doped with Er 3+ and co-doped with Er 3+–Tm 3+ are presented in this work. The luminescence properties have been characterized by absorption, excitation and emission spectra. All samples excited by blue light could emit a combination of blue/green/orange/red wavelength giving white light. For Er 3+-doped glasses, a self-quenching effect has been obtained and an adjustable tune comes out after crystallization. For co-doped glasses, the red emission at 651 nm has been enhanced due to the existence of Tm 3+, which could be relative to both the overlapped emissions and the energy transfer from Tm 3+ to Er 3+.

Electrical conductivity, relaxation, and scaling analysis studies of lithium alumino phosphate glasses and glass ceramics

Different compositions of lithium aluminum phosphate glasses were prepared by melt quenching technique. The best bulk conductivity achieved by the sample G3, (28 mol% of lithium oxide). Further, the investigation extended by crystallizing the G3 sample at different temperatures, 200 °C (GC200), 300 °C(GC300), 400 °C (GC400), and 500 °C (GC500). The electrical measurements for all the glasses and glass ceramics were carried out in the frequency range of 1–105 Hz and at a temperature range of 393–513 K by the impedance spectroscopy. The variation of conductivity with frequency of the samples was explained in the light of different valency states of aluminum ions. AC conductivity data are fitted to a power law equation. Scaled spectra for ac conductivity and modulus data suggested that the present glass samples follow temperature independent conductivity distribution relaxation mechanism.

Preparation and Characterization of the Neodymium-Doped Phosphate Glass-Ceramics

Preparation and Characterization of the Neodymium-Doped Phosphate Glass-Ceramics

Preparation and Luminescence Properties of Glass Ceramics Precipitated With $\hbox{M}_{\bf 2}\hbox{MgSi}_{\bf 2}\hbox{O}_{\bf 7}{:}\,\hbox{Eu}^{\bf 2+}$ (M = Sr, Ca) Phosphor for White Light Source

Eu2+-doped silicate glasses were prepared in the system 42SiO2- gammaCaO-(38gamma)SrO-20MgO- 0.2EuO (gamma = 0, 10, 20, 30, 38) by melting under reducing atmosphere. Glass ceramics precipitated with M2MgSi2O7:Eu2+ (M = Sr, Ca) phosphor were obtained by heat-treatment of the glass. They showed broad emission band due to the 5d rarr 4f transition of Eu2+. The peak wavelength shifted from 470 to 530 nm with increasing CaO content. Their emission wavelength can be controlled by changing the compositional ratio of Ca and Sr. Their color coordinates were widely changed from blue to yellowish green region. We have successfully obtained glass ceramic phosphors with excellent durability for a high-power white LED based on near-UV LED.

Novel $\hbox{Eu}^{{2+}}$-Activated Glass Ceramics Precipitated With Green and Red Phosphors for High-Power White LED

We have obtained Eu2+-doped glass-ceramic phosphors, where the two-phosphor crystals of green and red were precipitated by novel GC preparation frozen sorbet method and postceraming process. The as-made GC consisted of glass and spherical beta-Ca2SiO4:Eu2+ crystal phases with size of about 20-40 mum. After ceramization, Ca3Si2O7:Eu2+ crystals were also precipitated in addition to the beta-Ca2SiO4 crystal. The photoluminescence had two broad emission bands: at 515 nm from Eu2+ :beta-Ca2SiO4 and at 600 nm from Eu2+ :Ca3Si2O7. Judging from the cathodoluminescence mapping images of microstructure, two emission bands peaked at 515 and 600 nm were observed from different parts in the GC. With increasing heat-treatment temperature, the color coordinates shifted from green range to center region, which corresponds to pure white in the International Commission on Illumination chromaticity diagram. Eu2+-doped calcium silicate GC containing beta-Ca2SiO4 and Ca3Si2O7 are suitable phosphor as the use of phosphor converting white LED with high color rendering.

Temperature dependence of luminescence behavior in Er 3+/Yb 3+ co-doped transparent phosphate glass ceramics

The effect of temperature on the luminescence intensity of up-conversion and near infrared in Er 3+/Yb 3+ co-doped phosphate glass ceramics has been investigated. Efficient green and red up-conversion luminescence and strong infrared fluorescence at 1.54 μm wavelength are observed under excitation of 975 nm. The fluorescence intensity is changing at different temperature and the results are explained with the level transitions in Er 3+/Yb 3+ co-doped system. Meanwhile, the lifetime of Er 3+: 4I 13/2 level corresponding to different operating temperature and pump power is also discussed, and the experimental results are fitted using multiphonon relaxation theory.

Back Cover: Phys. Status Solidi A 206/5

AbstractThe back cover picture of this issue refers to the article entitled ‘Preparation and luminescent properties of Eu2+‐activated glass ceramic phosphor precipitated with β‐Ca2SiO4 and Ca3Si2O7’ by T. Nakanishi and S. Tanabe (pp. 919–922). The paper is a contribution from the International Conference on Optical, Optoelectronic and Photonic Materials and Applications (ICOOPMA) held in Edmonton, Canada in July 2008. The two left‐most pictures show the cathodoluminescence mapping images of the as‐made glass ceramic (GC) and a GC sample heat‐treated at 1050 °C, in which the secondary phase of red phosphor was precipitated around the primary crystal phase emitting green luminescence by post ceramization. The three sample pictures show the color variation of the photoluminescence from the GC phosphors of the same composition ceramed at different temperatures. The chromaticity diagram on the right hand side shows the change in the color coordinates through the ceramization (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of Ce3+ on the spectroscopic properties of transparent phosphate glass ceramics co-doped with Er3+/Yb3+

We have prepared Er3+/Yb3+ co-doped transparent phosphate glass ceramics by the high-temperature melting technique, and demonstrated the influence of energy acceptors Ce3+ ions on the up-conversion and 1.54μm emission properties of Er3+. The energy transfer mechanism is discussed based on the energy matching and the energy level structure. The phonon-assisted energy transfer between Er3+ and Ce3+ favors population feeding from the 4I11/2 to the 4I13/2 level, and therefore drastically decreases the up-conversion emission intensity of Er3+. Meanwhile, 1.54μm fluorescence enhances greatly with the introduction of Ce3+ ions at the proper concentration.

Light scattering in glass ceramic x-ray storage phosphors

We have performed numerical simulations to determine the modulation transfer function for glass ceramic x-ray imaging plates where the image readout is by a scanned laser beam. We focus, in particular, on the role of the effective scattering length in determining the width of the modulation transfer function, covering a range of scattering lengths describing very opaque to very transparent glass ceramics. We find that the shape of the modulation transfer function is, in general, bimodal, with a broad contribution from the laser beam width, and superimposed a narrow one from scattering. The overall width of the modulation transfer function reaches a minimum when the scattering length is comparable with the beam width, and so scattering lengths either much greater or less than the beam width, corresponding to either strongly scattering or highly transparent glass ceramics, give the best expected spatial resolution. However, for a practical range of scattering parameters, transparent glass ceramics are predicted to have a superior resolution compared to very opaque ones. Simulations are included which also demonstrate the effect of particle size, optical absorption, and readout laser power. Stronger optical absorption at the wavelength of the stimulating beam in comparison with that at the wavelength of the emitted light has a markedly beneficial effect on the spatial resolution at the expense of sensitivity. Simulation results are confronted with experimental results for a commercial BaFBr:Eu2+ powder-based imaging plate and a europium-doped fluorozirconate glass ceramic, and good agreement is obtained.

Luminescence Characteristics of YAG Glass-Ceramic Phosphor for White LED

Luminescence characteristics of Ce:Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> (YAG) glass-ceramic (GC) phosphor for a white LED were investigated. The GC phosphor was obtained by a heat treatment of a Ce-doped SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> mother glass between 1300degC and 1500degC for the prescribed time period. The quantum efficiency (QE) of Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> fluorescence in the GC materials, the color coordinate, and the luminous flux of electroluminescence of LED composite were evaluated with a blue LED (465 nm) set in an integrating sphere. The QE increased with increasing ceramming temperature of the as-made glass. The color coordinates ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> ) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelengths shifted to longer side up to Gd/(Y + Gd) = 0.40 in molar composition. As a result, the color coordinate of the LED with GdYAG-GC of various thickness shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions in the precipitated YAG microcrystals, leading to the increase of lattice constant of unit cell, which was confirmed by XRD.

Effect of phase separation on crystallization of glasses in the BaO-TiO2-SiO2 system

The effects of phase separation on the crystallization behavior of glasses were investigated in order to materialize a high-luminous glass-ceramic phosphor, which consists of fine phosphor crystals and a transparent glass matrix prepared due to phase separation. The glass ceramics in BaO-TiO2-SiO2 has the potential to show high photoluminescence intensity, because of multiple light scattering at the boundary between the phosphor crystal and the glass matrix. The crystallization behaviors of the glasses were examined using both the XRD analyses for an isothermal heat treatment process and the DTA measurements as a non-isothermal treatment process. The phase-separation in the glass significantly affected the subsequent crystallization behavior. In the non-phase-separated glasses, surface crystallization occurred first, and crystallization then proceeded inside the glasses. In the phase-separated glasses, the crystallization was considered to start at the boundary of two glass phases inside the glass and the crystals grew in BaO-TiO2-rich phases. This apparent bulk crystallization owing to the phase separation has the potential to materialize a high-performance phosphor composite.

Comparison of optical parameters and luminescence between Er3+/Yb3+ codoped phosphate glass ceramics and precursor glasses

Er 3 + / Yb 3 + codoped transparent phosphate precursor glasses and glass ceramics have been fabricated and characterized. The formation of ErPO4 and YbPO4 nanocrystals was studied using x-ray diffraction. The intensity parameters, the spontaneous radiative transition probabilities, the branching ratios, and the radiative lifetimes of Er3+ in both glass ceramics and precursor glasses were calculated based on the Judd–Ofelt theory, and the crystallization process in the glass ceramics is confirmed by the optical parameters obtained. Under 975 nm wavelength excitation intense 1.54 μm fluorescence and upconversion luminescence were observed in the glass ceramics, the quantum efficiency of the Er3+ I413/2→I415/2 transition is 95%, and the transition mechanisms of the upconversion luminescence are due to a two-photon process.

Ceramic and Glass Ceramic Phosphors for White LEDs

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In vitro behavior of bioactive phosphate glass–ceramics from the system P 2O 5–Na 2O–CaO containing titania

Soda lime phosphate bioglass–ceramics with incorporation of small additions of TiO 2 were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the soda lime phosphate glasses were performed using X-ray diffraction analysis. Calcium pyrophosphate (β-Ca 2P 2O 7), sodium metaphosphate (NaPO 3), calcium metaphosphate (β-Ca(PO 3) 2), sodium pyrophosphate (Na 4P 2O 7), sodium calcium phosphate (Na 4Ca(PO 3) 6) and sodium titanium phosphate (Na 5Ti(PO 4) 3) phases were detected in the prepared glass–ceramics. The degradation of the prepared glass–ceramics was carried out for different periods of time in simulated body fluid at 37 °C using granules in the range 0.300–0.600 mm. The released ions were estimated by atomic absorption spectroscopy and the surface textures were measured by scanning electron microscopy. Investigation of in vitro bioactivity of the prepared glass–ceramics was done by the measurement of the infrared reflection spectra for the samples after immersion in the simulated body fluid for different periods at 37 °C. The result showed that no apatite layer was formed on the surface of the samples and the dominant phase remained on the surface was β-Ca 2P 2O 7, which is known for its bioactivity.

Luminescence Characteristics of YAG Glass–Ceramic Phosphor for White LED

Luminescence characteristics of Ce:Y3Al5O12 (YAG) glass-ceramic (GC) phosphor for a white LED were investigated. The GC phosphor was obtained by a heat treatment of a Ce-doped SiO2-Al2 O3-Y2O3 mother glass between 1300degC and 1500degC for the prescribed time period. The quantum efficiency (QE) of Ce3+ fluorescence in the GC materials, the color coordinate, and the luminous flux of electroluminescence of LED composite were evaluated with a blue LED (465 nm) set in an integrating sphere. The QE increased with increasing ceramming temperature of the as-made glass. The color coordinates (x, y) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd2O3 substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelengths shifted to longer side up to Gd/(Y + Gd) = 0.40 in molar composition. As a result, the color coordinate of the LED with GdYAG-GC of various thickness shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd3+ ions in the precipitated YAG microcrystals, leading to the increase of lattice constant of unit cell, which was confirmed by XRD.

Preparation of BaSi2O5:Eu2+ Glass Ceramic Phosphors and Luminescent Properties

Eu2+-doped BaSi2O5 glasses were prepared by melting method and the glass-ceramics (GCs) were obtained by heat-treatment at various temperatures between 800 °C and 1000 °C. The single phase of BaSi2O5 micro-crystal precipitated in the GCs by heat-treatment above 950 °C, and the quantum yield (QY) of Eu2+ fluorescence became higher than that of other GCs, in which other crystal phases precipitated. When the BaSi2O5 precipitated, the QY increased drastically.