Infrared-to-visible conversion luminescence of Er3+ ions in lead borate transparent glass-ceramics

Transparent glass-ceramics were successfully prepared during controlled heat treatment of lead borate glasses. The PbF₂ particles were dispersed into a borate glass matrix which was evidenced by X-ray diffraction analysis. The phase identification revealed that crystalline peaks can be related to the orthorhombic PbF₂ phase. Green up-conversion luminescence due to the ⁴S_3/2–⁴I_15/2 transition of Er³⁺ ions was registered. In comparison to the precursor glass the luminescence intensity was considerably higher, whereas the luminescence linewidth slightly decreased in the studied oxyfluoride transparent glass-ceramics. It indicated that a part of the trivalent erbium was incorporated into the PbF₂ crystalline phase.     

Up-conversion luminescence and near infrared luminescence of Er3+ in transparent oxyfluoride glass-ceramics

The up-conversion luminescence and near infrared luminescence of the Er³⁺ in transparent oxyfluoride glass-ceramics have been investigated. The formation of PbF₂ nano-crystals in the glass was confirmed by XRD. From optical absorption spectra, the oscillator strengths for several transitions of the Er³⁺ in the glass and glass-ceramic have been obtained and then the Judd–Ofelt parameters were calculated by a least squares fitting. The split near infrared emission peaks of the Er³⁺ ions in the glass-ceramics can be observed because the Er³⁺ ions have entered into crystalline environment of the β-PbF₂ nano-crystals. The up-conversion luminescence intensity of the Er³⁺ in the glass-ceramics can be observed to be much stronger than that in the glasses. The dependence of the up-conversion luminescence intensity on the current of the LD laser used as excited source indicated that the transition mechanism of the up-conversion luminescence can be ascribed to two-photon absorption process.     

Frequency up-conversion luminescence in Yb3+–Ho3+ co-doped PbxCd1−xF2 nano-crystals precipitated transparent oxyfluoride glass-ceramics

Oxyfluoride glasses were developed with composition 30SiO₂·15AlO_1.5·28PbF₂·22CdF₂·(4.9−x)GdF₃·0.1HoF₃·xYbF₃ (x=0, 0.1, 0.2, 0.5, 1, 2, 3, and 4) in mol%. Powder X-ray diffraction analysis revealed that the heat-treatments of the oxyfluoride glasses at the first crystallization temperature cause the precipitation of Yb³⁺–Ho³⁺ co-doped fluorite-type nano-crystals of about 17.8 nm in diameter in the glass matrix. These transparent glass-ceramics exhibited very strong green up-conversion luminescence due to the Ho³⁺: (⁵F₄, ⁵S₂)→⁵I₈ transition under 980 nm excitation. The intensity of the green up-conversion luminescence in the glass-ceramics was much stronger than that in the precursor oxyfluoride glass. The reasons for the highly efficient Ho³⁺ up-conversion luminescence in the oxyfluoride glass-ceramics are discussed.     

Eu ions and CaF2-containing transparent glass-ceramics

Transparent glass-ceramics have been prepared by heat-treating 45SiO₂-20Al₂O₃-10CaO-25CaF₂ glasses doped with Eu²⁺ ions (in mol%). The precipitated crystalline phase in the glass-ceramics was CaF₂. TEM observation showed the precipitated crystalline phase had a size of 11-18 nm and dispersed in the amorphous phase without clustering. Fluorescence measurements showed that Eu²⁺ ions entered into the CaF₂ crystalline phase and gave a much stronger emission in the glass-ceramics than in the corresponding glass.     

Optical investigation of Eu:PbF2 ceramics and transparent glass-ceramics

This paper reports an optical investigation of glass-ceramics formed by annealing glasses with compositions 50 GeO₂-40 PbO-10 PbF₂-x EuF₃, x = [0.5; 1; 1.5; 2] and polycrystalline ceramics with composition 100 PbF₂, y EuF₃, with y = 5, 10, 15 and 20. For each material, the photoluminescence spectrum and the photoluminescence lifetimes of the ⁵D₀, ⁵D₁ and ⁵D₂ Eu³⁺ levels are measured. Occurrence of Eu³⁺:β-PbF₂ nanocrystallites in the glass-ceramics is confirmed and total ceramisation requires more than 10% of EuF₃ with respect to PbF₂ in the starting glass.In the Eu³⁺:β-PbF₂ ceramics and glass-ceramics, Eu³⁺ ions replace Pb²⁺ in their regular cubic site, but they interact together to form dimers and higher nuclearity clusters. These two species are easily distinguished according to their photoluminescence decay rate. For the EuF₃ rates investigated here, there are no isolated Eu³⁺ ions in the PbF₂ lattice.A preliminary investigation of the optical properties of co-doped Gd³⁺:Eu³⁺:β-PbF₂ ceramics was also performed. It shows that mixed Gd³⁺-Eu³⁺ dimers and clusters are formed, and that efficient Gd³⁺ → Eu³⁺ energy transfer occurs in these ceramics. The Pb²⁺ ions of the lattice may also be involved in the energy transfer process.     

Anomalous crystallization behavior of strontium titanate aluminosilicate glass-ceramics

The crystallization of glasses with a nominal composition consisting of 65 wt% SrTiO₃, 29 wt% SiO₂, and 6 wt% Al₂O₃, were investigated. Two glass batches of this composition, prepared from different chemicals and similar processing conditions, resulted in glass-ceramics with very different crystalline phases. One glass batch resulted in glass-ceramics with perovskite SrTiO₃ as the primary crystalline phase, while the second glass batch resulted in glass-ceramics with fresnoite Sr₂TiSi₂O₈ as the primary crystalline phase. The different crystallization sequences of glass-ceramics of the two glass batches were traced to differences between the first phases to crystalline from each glass. The crystallization behavior of these glass-ceramics was further complicated by the presence of several unidentified phases.     

Structural characterisation of transparent oxyfluoride glass-ceramics

Erbium doped transparent glass-ceramics were obtained in the family (50GeO₂[50–y]PbO, yPbF₂+xErF₃). With controlled crystallisation of glasses by inhomogeneous nucleation and growth during reheating, PbF₂ crystallites of nanometric size and a filling factor of 10^–2 were obtained. The phase separation process was studied by thermal analysis, X-ray diffraction and Transmission Electron Microscopy as a function of the precursor glass composition and thermal treatments. The Raman spectra were also measured.     

Effect of CdF2 addition on thermal stability and upconversion luminescence properties in Tm–Yb codoped oxyfluoride silicate glasses

Tm³⁺–Yb³⁺ codoped oxyfluoride silicate glasses suitable for upconversion laser has been fabricated. In this paper, effect of CdF₂ addition on thermal stability and upconversion luminescence properties in Tm³⁺–Yb³⁺ codoped oxyfluoride silicate glasses have been systematically investigated. The experimental results indicate that, with the substitution CdF₂ for PbF₂, the glass thermal stability increases and the UV cutoff edge moves to short-wave band slightly. With increasing CdF₂ content, the blue and red upconversion luminescence intensity increases slightly at first, and then increases rapidly. While the near infrared (NIR) upconversion emission intensity increases notably at first and then increases slightly. However, the blue and NIR luminescence intensity are much stronger than that of red, indicating these oxyfluoride silicate glasses are more preferable for blue and NIR emissions than red emission. The possible upconversion mechanisms for the blue, red and NIR fluorescence are also estimated and evaluated.     

Transparent Ni-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence

We report transparent Ni²⁺-doped ZnO-Al₂O₃-SiO₂ system glass-ceramics with broadband infrared luminescence. After heat-treatment, ZnAl₂O₄ crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. No infrared emission was detected in the as-prepared glass samples, while broadband infrared luminescence centered at 1310 nm with full width at half maximum (FWHM) of about 300 nm was observed from the glass-ceramics. The peak position of the infrared luminescence showed a blue-shift with increasing heat-treatment temperature, but a red-shift with an increase in NiO concentration. The mechanisms of the observed phenomena were discussed. These glass-ceramics are promising as materials for super broadband optical amplifier and tunable laser.     

Fluorescence properties and energy transfer mechanism of Sm ion in lead telluroborate glasses

We report the fluorescence properties of Sm³⁺-doped lead telluroborate glasses of composition PbF₂.TeO₂.H₃BO₃.Sm₂O₃ as a function of Sm³⁺ concentration. A Judd-Ofelt scheme was used to determine the intensity parameters and radiative properties of Sm³⁺ ion. The emission and decay measurements were carried out at 402 nm excitation. Beyond 1.0 mol% Sm³⁺ concentration, the luminescence quenching is observed. The decay curves of ⁴G_5/2 level are well fitted to a single exponential function. The evaluated radiative properties suggest that the ⁴G_5/2 → ⁶H_7/2 transition is responsible for reddish-orange luminescence which might be used in the development of visible lasers.     

Luminescence behavior of Dy ions in lead borate glasses

Dy-doped lead borate glasses were studied. The luminescence spectra showed two characteristic bands at 480 and 573 nm due to ⁴F_9/2–⁶H_15/2 (blue) and ⁴F_9/2–⁶H_13/2 (yellow) transitions of Dy³⁺. The yellow/blue luminescence of trivalent dysprosium was analyzed as a function of the B₂O₃/PbO ratios, the activator (Dy³⁺) and the PbX₂ (X = F, Cl, Br) content.     

Crystallization study of (TiO2, ZrO2)-rich SiO2-Al2O3-CaO glasses Part I Preparation and characterization of zirconolite-based glass-ceramics

Nuclear power reactors generate long-lived radionuclides such as minor actinides (Np, Am, Cm) which are mainly responsible for the long term radiotoxicity of high level nuclear wastes obtained after reprocessing of nuclear spent fuel. Specific highly durable matrices such as glass-ceramics appear as good candidates for the immobilization of minor actinides. This work concerns the synthesis and the characterization of zirconolite (CaZrTi₂O₇) based glass-ceramics prepared by controlled devitrification of (TiO₂, ZrO₂)-rich SiO₂-Al₂O₃-CaO parent glasses for which neodymium was selected to simulate the radioactive trivalent minor actinides. The present study reports the effect of increasing TiO₂, ZrO₂ and CaO amounts in glass composition on the structure and the composition of the zirconolite crystals (formed as the only crystalline phase in the bulk of the glass), on their nucleation rate I(Z) and on the volume proportion of crystalline phase V of the glass-ceramics. It appears that I(Z) and V strongly increase when the parent glass composition changes. Neodymium electron spin resonance (ESR) shows that the total amount of Nd³⁺ ions incorporated in the zirconolite phase increases with TiO₂, ZrO₂ and CaO amounts in parent glass composition.     

熔制保温时间对CAMS系矿渣微晶玻璃结构与性能的影响

以白云鄂博二次选后尾矿、高炉渣和粉煤灰为主要原料,采用熔融法制得CaO-Al_2O_3-MgO-SiO_2(CAMS)系微晶玻璃,利用DSC、XRD、SEM、EDS、Raman、红外光谱及理化性能测试手段,研究了熔制过程中不同保温时间对微晶玻璃结构与性能的影响。结果表明:随着熔制保温时间的延长,矿渣玻璃熔液中氟的挥发及对氧化铝坩埚的侵蚀导致基础玻璃中氟含量降低而Al2O3含量升高,基础玻璃析晶温度呈先上升后下降的趋势,微晶玻璃主晶相为透辉石,晶粒出现先细化后粗化的趋势,第二相萤石相随着保温时间的延长逐渐消失,最终导致微晶玻璃结构及理化性能发生改变。当玻璃熔制保温时间为5h时,制备的微晶玻璃综合性能最优,其密度、抗折强度、显微硬度及耐酸碱性分别为3.09g/cm3、201 MPa、7 021 MPa、97.78%和98.83%。     

Effect of solubility YAG:Nd nanocrystals in glass matrix

The nanocomposites of Y₃Al₅O₁₂:Nd³⁺ (YAG:Nd) incorporated in borate glass were obtained. The single phase of YAG:Nd nanocrystals were obtained by sol-gel method. The borate glass was melted first and ground up then mixed with the nanocrystals. The samples were formed into pellets under pressure and were annealed in temperatures from the range 550-800 °C. The X-ray diffraction patterns show that together with increasing the temperature the contribution of Y₃Al₅O₁₂ phase decreases and the new YBa₃B₉O₁₉ phase is observed. The luminescence measurements indicates that the band structures and distribution of band intensities of glass-YAG:Nd nanocrystal composites depends crucially on annealing temperature.     

Spectroscopic properties of Pr3+ and Er3+ ions in lead-free borate glasses modified by BaF2

Lead-free oxyfluoride borate glasses singly doped with Pr³⁺ and Er³⁺ were prepared and next investigated using absorption and luminescence spectroscopy. In the studied glass system, barium oxide was substituted by BaF₂. Two luminescence bands of Pr³⁺ located at visible spectral region are observed, which correspond to ³P₀–³H₄ (blue) and ¹D₂–³H₄ (reddish orange) transitions, respectively. The luminescence bands due to ¹D₂–³H₄ transition of Pr³⁺ are shifted to shorter wavelengths, when BaO was substituted by BaF₂. Near-infrared luminescence spectra of Er³⁺ ions in lead-free borate glasses modified by BaF₂ correspond to ⁴I_13/2–⁴I_15/2 transition. Their spectral linewidths increase with increasing BaF₂ concentration. The changes in measured lifetimes of rare earth ions are well correlated with the bonding parameters calculated from the optical absorption spectra.     

Influence of MO/MF2 modifiers (M = Ca,Sr, Ba) on spectroscopic properties of Eu3+ ions in germanate and borate glasses

Series of Eu³⁺-doped lead-free germanate and borate glasses were synthesized. The MO glass modifiers (M = Ca, Sr or Ba) were partially or totally substituted by MF₂ in chemical composition. In contrast to samples modified by CaO/CaF₂ or SrO/SrF₂, the germanate glass samples containing BaO and/or BaF₂ are fully amorphous, while the lead-free borate glasses are fully amorphous, independently from glass modifiers. Effect of glass modifiers on spectroscopic properties of Eu³⁺ were systematically investigated.For that reason, excitation and emission spectra of Eu³⁺ ions in examined systems were registered. Based on the emission spectra, ratio of integrated luminescence intensity of the ⁵D₀ → ⁷F₂ transition to that of the ⁵D₀ → ⁷F₁ transition (R factor) was calculated. Moreover, the luminescence decay curves were collected and the luminescence lifetimes of the ⁵D₀ excited state of Eu³⁺ ions were determined in function of MF₂ concentration.     

Study of fluorine losses and spectroscopic properties of Er doped oxyfluoride silicate glasses and glass ceramics

The fluorine losses during synthesis of Er³⁺ doped transparent glasses in the SiO₂–PbO–PbF₂ system were investigated. The final fluorine contents of the glasses were detected by using a fluorine ion selective electrode. The results show that high fluorine losses are occured in the normal preparation processes. With the increase of initial PbF₂ contents or melting time resulted in the increase of the fluorine losses. The thermal and spectroscopic properties of the glasses and the corresponding glass ceramics were investigated through the analysis of the differential scanning calorimetry (DSC), absorption and upconversion luminescence spectra. The effects of fluorine contents show a decrease of the glass transition temperatures (Tg) of the glasses and an enhancement of upconversion intensity of the corresponding glass ceramics.     

The microstructure of erbium-ytterbium co-doped oxyfluoride glass-ceramic optical fibers

Oxyfluoride transparent glass-ceramics combine some features of glasses (easier shaping or lower than single crystals cost of fabrication) and some advantages of rare-earth doped single crystals (narrow absorption/emission lines and longer lifetimes of luminescent levels). Since the material seems to be promising candidate for efficient fiber amplifiers, the manufacturing as well as structural and optical examination of the oxyfluoride glass-ceramic fibers doped with rare-earth ions seems to be a serious challenge. In the first stage oxyfluoride glasses of the following compositions 48SiO₂-11Al₂O₃-7Na₂CO₃-10CaO-10PbO-11PbF₂-3ErF₃ and 48SiO₂-11Al₂O₃-7Na₂CO₃-10CaO-10PbO-10PbF₂-3YbF₃-1ErF₃ (in molar%) were fabricated from high purity commercial chemicals (Sigma-Aldrich). The fabricated glass preforms were drawn into glass fibers using the mini-tower. Finally, the transparent Er³⁺ doped and Er³⁺/Yb³⁺ co-doped oxyfluoride glass-ceramic fibers were obtained by controlled heat treatment of glass fibers. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. X-ray diffraction examination (XRD) at each stage of the glass-ceramic fibers fabrication confirmed the undesirable crystallization of preforms and glass fibers has been avoided. The fibers shown their mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. The crystal structure of the grown nano-crystals has been determined by XRD and confirmed by electron diffraction (SAED). Results obtained by both techniques seem to be compatible: Er₃FO₁₀Si₃ (monoclinic; ICSD 92512), Pb₅Al₃F₁₉ (triclinic; ICSD 91325) and Er₄F₂O₁₁Si₃ (triclinic; ICSD 51510) against to initially expected PbF₂ crystals.     

New binary PbF2-AlF3 glasses

New binary glass PbF₂-AlF₃ (AlF₃ 30–60 mole %) is developed by rapid quenching technique. PbF₂-AlF₃ glass, which is resistant to moisture and of low toxicity, is expected to have a transmission loss minimum in 3–4 μm wavelength region. Infrared absorption edge of the glass is originated from AlF₃ absorption band around 18 μm. Refractive index of PbF₂-AlF₃ glass is measured as 1.66 the value decreases with increasing AlF₃ content. Crystallization temperature (280–330°C) and thermal expansion coefficient (13?16×10^?6) are also affected by AlF₃ content. Activation energy of crystallization is determined, by DTA measurement, as about 80 kcal/mole. It is suggested from these data that PbF₂-AlF₃ glass has a potentiality for the achievement of infrared transmitting optical fibers.     

Ionic conductivity of fluoroaluminoindate glasses

(54 - 2.4x)InF₃ + xA1F₃ + (36 -1.6x)BaF₂ + 3xPbF₂ + 1OLiF glasses (nine compositions,x varying from 0 to 18 mol % at 2.25 mol % intervals) were prepared. The glass compositions were taken between the 60InF₃ + 40BaF₂ and 25A1F₃ + 75 PbF₃ eutectics, of which the former is glass-forming (10 mol % LiF was added for glass stabilization). The electrical properties of the glasses were studied by impedance spectroscopy at frequencies from 5 Hz to 500 kHz and temperatures from 20 to 200‡C. The 400-K ionic conductivity of the glasses was found to rise from 4.3 x 10^-6 S/cm in the PbF₂-free glass to 1.4 x 10^-5 S/cm in the glass containing 54 mol % PbF₂; concurrently, the 300-K static dielectric permittivity increases from 17 to 29.