Spectroscopic properties of Er-Yb co-doped glass ceramics containing BaF2 nanocrystals

A Er³⁺ and Yb³⁺ co-doped transparent oxyfluoride glass ceramic containing BaF₂ nanocrystals has been prepared. The formation of BaF₂ nanocrystals in the glass ceramic was confirmed by X-ray diffraction. Intense upconversion luminescence in the Er³⁺ and Yb³⁺ co-doped glass ceramic could be observed. Stark splitting of the Er³⁺ upconversion luminescence peaks in the glass ceramic indicated that Er³⁺ and Yb³⁺ had been incorporated into the BaF₂ nanocrystals. Near infrared luminescence decay curves showed that the Er³⁺ and Yb³⁺ co-doped glass ceramic had higher luminescence efficiency than the precursor glass.     

Investigation of the crystallization process in oxyfluoride glass ceramics codoped with Er/Yb

The oxyfluoride glass ceramics are important up-conversion luminescent materials. Er³⁺/Yb³⁺-codoped transparent oxyfluoride glasses were prepared by melt-quenching and subsequently heat-treated at different times and temperatures, and the crystallization process of fluoride nanocrystals from the glass was investigated. X-ray diffraction (XRD) and fluorescence spectra investigations reveal that fluoride nanocrystals are distributed homogeneously among the glassy matrix for the sample doped with Er³⁺/Yb³⁺. The crystallization process indicates that heat-treatment temperature influences the size of fluoride nanocrystals, while heat-treatment time influences their concentration. Moreover, the red emission intensities increase due to the incorporation of Er³⁺/Yb³⁺ into the fluoride nanocrystals under different heat-treatment methods, which are studied by fluorescence spectra.     

Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Transparent oxyfluoride glass-ceramic in the system SiO₂–Al₂O₃–CaF₂–EuF₂ containing Eu-doped CaF₂ nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF₂ nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu³⁺ ion along with annealing time which is consistent with the Eu³⁺ environment evolving from a glassy to a crystalline state.     

Preparation and spectral properties of Nd3 +-doped transparent glass ceramic containing Ca5(PO4)3F nanocrystals

A Nd^3 +-doped transparent oxyfluoride glass ceramic containing Ca₅(PO₄)₃F nanocrystals was prepared by thermal treatment at the crystallization temperature for the precursor glass. The transmittances of the precursor glass and the glass ceramic with a thickness of about 2 mm are up to 84.7% and 77.4% in the visible range. The volume fraction of Ca₅(PO₄)₃F nanocrystals in the glass ceramic is about 19% and the ingress fraction of Nd^3 + ions into the Ca₅(PO₄)₃F nanocrystals is about 32%. The peak absorption cross-section increases to 224% at 807 nm and the full width at half maximum for the 807 nm band decreases from 17.5 to 3.5 nm after the crystallization process. The peak stimulated emission cross-section increases from 1.89 × 10^? 20 to 2.42 × 10^? 20 cm² at 1062 nm and the effective width of the emission line for the 1062 nm band decreases from 34 to 29 nm after the crystallization process. The improvement of spectroscopic properties indicates that the glass ceramic is potentially applicable as the 1.06 μm laser material.     

Enhanced luminescent properties of Tb3+ ions in transparent glass ceramics containing BaGdF5 nanocrystals

Tb³⁺ doped transparent oxyfluoride glass ceramics containing BaGdF₅ nanocrystals were prepared. The transmission spectra, photoluminescence spectra, decay time and X-ray excited luminescence spectra of the Tb³⁺-doped glass and glass ceramics were investigated. Energy transfer from Gd³⁺ to Tb³⁺ has been observed in the glass and glass ceramics. The emission intensity of green band (⁵D₄ → ⁷F_J) of the Tb³⁺-doped glass ceramics is enhanced compared with that of the glass under ultraviolet and X-rays, which could be attributed to that the generation of BaGdF₅ nanocrystals with low phonon energy reduces the non-radiative transitions.     

Effects of Li replacement on the nucleation, crystallization and microstructure of Li2O-Al2O3-SiO2 glass

The Li replacement including the Li₂O replaced by other oxides and the expensive Li₂CO₃ replaced by low-cost spodumene mineral was studied to lower the product cost of (Li₂O-Al₂O₃-SiO₂, LAS) glass ceramic, and the effects of Li replacement on the nucleation, crystallization and microstructure of LAS glass were investigated by the differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that Li₂O replacement increases the crystallization activation energy, lowers the crystal growth, and increases the nucleation and crystallization temperature by restraining the formation of crystalline phases. The Li₂CO₃ replacement decreases the crystallization activation energy, promotes the crystal growth, without affecting the nucleation, and lowers the crystallization temperature by adding some beneficial compositions with mixed alkali effect.     

Luminescence behavior of Er ions in glass-ceramics containing CaF2 nanocrystals

The upconversion luminescence and near infrared luminescence of the Er³⁺ ions in transparent oxyfluoride glass-ceramics containing CaF₂ nanocrystals have been investigated. The formation of CaF₂ nanocrystals in the glass-ceramics was confirmed by XRD. The oscillator strengths for several transitions of the Er³⁺ ions in the glass and glass-ceramics have been obtained and then the Judd-Ofelt parameters were calculated. The split near infrared emission peaks of the Er³⁺ ions in the glass-ceramics can be observed because the Er³⁺ ions have been incorporated into crystalline environment of the CaF₂ nanocrystals. The upconversion luminescence intensity of Er³⁺ ions in the glass-ceramics increased significantly with increasing heat treated time. The transition mechanism of the upconversion luminescence has been ascribed to a two-photon absorption process.     

Non-isothermal crystallization kinetics of ZnO-BaO-B2O3-SiO2 glass

Glass of composition 40SiO₂-30BaO-20ZnO-10B₂O₃ (mol%) was made by conventional melting and casting process. Crystallization kinetics of above glass has been investigated under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The procedure is applied to the experimental data obtained by differential thermal analysis (DTA), using continuous-heating techniques. The crystallization results are analyzed, and both the activation energy of crystallization process as well as the crystallization mechanism is characterized. Dilatometric measurement of this glass was also done and data obtained was used to calculate the viscosity of the formed glass. Development of crystalline phases on thermal treatments of the glass at various temperatures has been analyzed by X-ray diffraction. Microstructure of the crystalline phases was investigated by scanning electron microscopy (SEM) and the development of various structural features with variation in heat treatment cycle was observed. The nucleation and growth of these phases in the matrix of glass has been described and discussed.     

Study on photoluminescence properties of oxyfluoride germanate Glass

The oxyfluoride germanate glass and glass-ceramics were prepared by the melting–annealing method. The composition of the glass was chosen as 45GeO2–30BaF2–5B2O3–15AL2O3–5R2O–xSm2O3 (R = Li, Na, and K. x = 1.5, 2.0, and 2.5, mol%). Differential thermal analysis, X-ray diffraction, and photoluminescence spectra were carried out to study the effects of the concentration of Sm ions, the kinds of alkali ions and heat treatment on the photoluminescence properties of Sm ion doped oxyfluoride germanate glass. The results showed that the luminescence intensity of the oxyfluoride germanate glass increased when x changed from 1.5 to 2.0 and then decreased when x changed from 2.0 to 2.5. Among various R2O, the Li2O included glass has the strongest luminescence intensity among all the glasses. Heat treatment at 660 °C for 4 h resulted in the formation of the Ba3AlF9 nanocrystal and enhanced the luminescence intensity of the sample. The mechanism of luminescence intensity increase was discussed.     

Synthesis of tin oxide nanosized crystals embedded in silica matrix through sol–gel process using alkoxide precursors

Materials made of tin oxide nanocrystals homogeneously dispersed into a silica glass matrix have been elaborated through sol–gel processing. Addition of strong acids was used to control the hydrolysis–condensation in tin and silicon alkoxides mixed alcoholic solutions. Fourier transform infrared spectroscopy (FTIR) and Small angle X-ray scattering (SAXS) measurements show that the introduction of HCl allows to synthesize gels containing up to 50% of tin oxide precursor without significant modification of the pure silica gel network. Thermal treatments of slowly dried bulk gels induce the crystallization of tin oxide nanoparticles. After firing at 1000 °C, dense materials containing tin oxide nanocrystals (with a mean diameter close to 1–2 nm) are obtained. The crystal size distribution was estimated by X-ray diffraction line profile analysis. The narrowness of this distribution makes these materials interesting for optical applications.     

Reduction and luminescence of europium ions in glass ceramics containing SrF2 nanocrystals

Reduction of Eu³⁺ → Eu²⁺ and luminescence of europium (Eu) ions in glass ceramics containing SrF₂ nanocrystals have been investigated. The formation of SrF₂ nanocrystals in glass ceramics was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Blue luminescence of the Eu²⁺ ions was observed in the Eu doped glass ceramics which were prepared by the heat treatment of the glass in air atmosphere. The double-exponential decay curves of ⁵D₀ state of Eu³⁺ in the Eu doped glass ceramics indicated that there were two different surroundings of the Eu ions in the glass ceramics.     

Crystallization kinetics of fluoride nanocrystals in oxyfluoride glasses

Oxyfluoride glasses containing different alkaline earth fluoride (CaF₂, SrF₂, and BaF₂) were prepared and their crystallization behavior was analyzed using non-isothermal kinetics based upon differential scanning calorimetry (DSC) scan results. The glass containing CaF₂ showed the fastest kinetics for CaF₂ crystallization, while that containing BaF₂ showed the slowest kinetics for BaF₂ crystallization. On the other hand, all the oxyfluoride glasses showed very similar behavior in the crystallization of glass matrices. The difference in the crystallization behavior of the oxyfluoride glasses was discussed based upon the difference in the size of alkaline earth ions and the difference in the dissociation energy of alkaline earth-fluorine bonds.     

Determination of the influence of TiO2 on the elastic properties of a mica based glass ceramic by ultrasonic velocity measurements

The influence of small amount (1 or 2 wt%) of TiO₂ additions and crystallization heat treatment on the elastic properties of a mica based glass ceramic have been investigated by ultrasonic velocity measurements. The mica based glass ceramic was prepared through controlled crystallization of a glass in the SiO₂, Al₂O₃, CaO, MgO, K₂O and F system. Evidences of TiO₂ acting as a nucleating agent in this system was demonstrated. The longitudinal and transversal wave velocities of the as-prepared glass and the mica based glass ceramic were measured by using 5 MHz probes at room temperature. Elastic properties namely; longitudinal modulus, Young’s modulus, bulk modulus, and shear modulus were calculated from the ultrasonic velocity values measured and density values obtained experimentally. It has been observed that small amount of TiO₂ additions caused a notable but not significant; however, the crystallization heat treatment had a profound effect on the elastic properties of the glass in the system studied.     

Structural changes during the crystallization of the Bi4Ge3O12 glasses

Bismuth-germanate glass ceramics with the composition 40% Bi₂O₃-60% GeO₂ (in molar percents) were prepared through controlled crystallization of melt-quenched glass. The Raman and FTIR spectra recorded in the as-made glasses show broad bands at 240, 400, 780 cm^− 1 and 400, 745 cm^− 1 have been assigned Ge-O bonds which appear right after preparation. X-ray diffraction has shown that the as-made glasses are amorphous, but after annealing above the crystallization temperature at 558 °C, BGO nano-crystallites with a size of about 50 nm precipitate in the glass matrix. The Raman and FTIR spectra reveal sharp peaks associated to the “internal” and “external vibrations” of GeO₄ tetrahedral groups inside the BGO nano-crystallites. In the glass ceramic sample the transparency region is shifted at longer wavelengths compared to as-made glass, due to the Rayleigh scattering on the BGO nano-crystallites.     

The influence of Ta2O5 additions on the thermal properties and crystallization kinetics of a lithium zinc silicate glass

The lithium zinc silicate glass exhibits two crystallization exotherms corresponding to the formation of Li₂ZnSiO₄ and silica phases, respectively. The silica phases include tridymite and cristobalite. The influence of Ta₂O₅ additions on the thermal properties and non-isothermal crystallization kinetics of this glass, including nucleation rate maxima and activation energies for crystallization, has been determined by differential scanning calorimetry and X-ray diffraction. It has been found that Ta₂O₅ affects the crystallization behavior markedly, inhibiting the crystallization of high thermal expansion silica phases at lower concentrations, whilst at higher concentrations also suppressing crystallization of the Li₂ZnSiO₄ phase. At the higher concentrations, these phases are replaced by small amounts of LiTaO₃ and LiTaSiO₅.     

Amorphous phase separation and crystallization in a lithium silicate glass prepared by the sol-gel method

A 10Li₂O---90SiO₂ (mol%) gel-glass has been prepared by using tetramethyl orthosilicate and lithium iso-propoxide as starting materials. The phase separation and crystallization behaviour was compared with the corresponding conventionally melted glass using DTA, X-ray diffraction and TEM. The same crystallization phase was found in both the gel glass and melted glass upon heating above 650°C. However, the rate of crystallization in the gel-glass was higher than in the melted glass. TEM revealed amorphous phase separation in the gel glass and melted glass. However, the morphologies were different, an interconnected microstructure being observed in the gel glass and a droplet structure in the melted glass. These differences can be partly attributed to differences in OH content. Other potential influencing factors are also considered. After 650°C for 2 h lithium disilicate crystals were observed in the volume of the gel glass by TEM. As the crystals grew they absorbed Li₂O from the surrounding lithia-rich amorphous phase so that silica-rich (lithia depleted) diffusion zones formed around them.     

A new transparent oxyfluoride glass ceramic with improved luminescence

A new type of glass ceramic containing BaF₂ nano-crystals was prepared by melt quenching. Differential scanning calorimetry, X-ray diffraction and transmission electron microscopy were used to study its thermal behaviors and structural characteristics. Based on Judd-Ofelt theory, the spectroscopic properties of the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ in glass ceramic were evaluated. Notably, it is found that the fluorescence lifetime in the present system is much longer than that in most other glasses and glass ceramics. A comparative study on luminescence performance suggests that the obtained glass ceramic is a promising material for Er³⁺ doped fiber amplifiers.     

AIT玻璃衬底非晶硅薄膜的固相晶化研究

本实验在铝诱导织构的基础上,对以AIT浮法玻璃为衬底沉积非晶硅薄膜固相晶化进行了初步研究.采用拉曼散射、X射线衍射等手段对生成多晶硅薄膜的结构和光学性能进行了表征和分析.研究结果表明:热处理10h,薄膜的晶化率达到80;以上,同时具有良好的(111)择优取向;同平板玻璃衬底对比,AIT玻璃上制备的多晶硅薄膜具有良好的陷光作用.     

Degree of local structural ordering and its correlation with the glass forming ability of alloys

The degree of local structural order in amorphous solids and liquids has been investigated in CuHf alloys for the first time. X-ray diffraction experiments and thermal analysis show that the local structural order is strongly composition-dependent. For the CuHf alloys, it has been found that a close relationship exists between the degree of local ordering and the glass forming ability. Comparisons between the present alloys and those studied previously show that local structural order in glass formation is determined by the dominant vitrification conditions (diffusion-controlled or nucleation-controlled). The local ordering structures act as random fields against crystallization when the primary crystallization mechanism for the undercooled melts is the formation of intermetallic crystals.