Local vibration around rare earth ions in alkaline earth fluorosilicate transparent glass and glass ceramics using Eu probe

By heat treating the alkaline earth fluorosilicate glass, transparent glass ceramics containing alkaline earth fluoride nanocrystallites were prepared. The luminescence spectra and phonon sideband associated with the Eu^3＋：^5D2→^7F0 in glass and glass ceramics were investigated to analyze the local environment around Eu^3＋. Judd-Ofelt parameters were also calculated from emission spectra, which indicated that the Eu^3＋ ions entered the precipitated CaF2, SrF2, and BaF2 nanocrystallites. Heat treating could not pledge Eu^3＋ ions to coordinate with F^- in the precipitated MgF2 nanocrystallites, owing to the smaller radius of Mg^2＋ than that of Eu^3＋.     

Effect of alumina content and heat treatment on microstructure and upconversion emission of Er3+ions in oxyfluoride glass-ceramics

The effect of alumina content and heat treatment temperature and time, on microstructure and Er3+ (0.5 mol.%) emission of oxy-fluoride glass-ceramics were investigated in this research. Two values of 1.8 (SA1.8Er0.5) and 2.18 (SA2.18Er0.5) were selected in this re-search for SiO2/Al2O3 ratio. According to DTA results, precursor glasses were heat treated at 630, 660 and 690 °C for 4 h and some glasses were also heat treated at 630 °C for 48 and 72 h. The results indicated that alumina content had significant effect on phase separation and vis-cosity of the glasses. Therefore the size, size distribution, and volume concentration of nano CaF2 crystals which precipitated during the heat treatment depended on alumina content of the glass. Due to the much smaller size of the precipitated CaF2 crystals in the glasses of low alumina content, these samples maintained excellent transparency and had narrower crystal size distribution than the high alumina glasses. The crystal size was increased markedly with the temperature increasing from 630 to 690 °C. On the other hand a slight increase was observed in the crystal size by raising the heat treatment time in both glasses. Results indicated that in low alumina content glass (SA2.18Er0.5) the size of CaF2 nanocrystals was controlled in one order of magnitude. The increase of heat treatment time and temperature led to the incorporation of Er3+ ions into CaF2 crystalline phase, increasing significantly the upconversion intensity. After heat treatment at 690 ℃ for 4 h, atomic force microscope (AFM) re-vealed the development of small crystals with an average size of 80 and 30 nm in SA1.8Er0.5 and SA2.18Er0.5 samples, respectively.     

Up-conversion of Er3＋/yb3＋ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals

The up-conversion of Er3+/Yb3+co-doped transparent glass-ceramics 50SiO2-10AlF3-5TiO2-30BaF2-4LaF3-0.5ErF3-0.5YbF3 containing Ba2 LaF7 nanocrystals under the changing of heat treatment temperature and time were investigated.The Ba2 LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction(XRD).The structural investigation carried out by XRD and transmission electron microscopy(TEM) evidenced the formation of cubic Ba2 LaF7 nanocrystals with crystal size of about 14 nm.Comparing with the samples before heat treatment,the high efficiency up-conversion emission of Er3+/Yb3+co-doped samples was observed in the glass-ceramics under 980 nm laser diode excitation.The increase in red emission intensity bands was stronger than the green bands when the crystal size increased.The mechanism for the up-conversion process in the glass-ceramics and the reasons for the increase of Er3+/Yb3+co-doped up-conversion intensity after heat treatment were discussed.     

Photoluminescent properties of Eu3＋ and Tb3＋ codoped Gd2O3 nanowires and bulk materials

In this paper, the Gd2O3：Eu3＋,Tb3＋phosphors with different doping concentrations of Eu3＋and Tb3＋ions were prepared by a hydrothermal method for nanocrystals and the solid-phase method for microcrystals. The interaction of the doped ions with different concentrations and the luminescent properties of the nanocrystals and microcrystals were studied systematically. Their structure and morphology of Gd2O3：Eu3＋,Tb3＋phosphors were analyzed by means of X-ray powder diffraction （XRD）, transmission electron mi-croscopy （TEM） and scanning electron microscopy （SEM）. The photoluminescence （PL） properties of Gd2O3：Eu3＋,Tb3＋phosphors were also systematically investigated. The results indicated that when the concentration of doped Eu3＋was fixed at 1 mol.%, the emis-sion intensity of Eu3＋ions was degenerating with Tb3＋content increasing, while when the Tb3＋content was fixed at 1 mol.%, the emission intensity of Tb3＋ions reached a maximum when the concentration of Eu3＋was 2 mol.%, implying that the energy transfer from Eu3＋to Tb3＋took place. In addition, Tb3＋could inspire blue-green light and the Eu3＋could inspire red light. Therefore co-doping systems by controlling the doping concentration and the hosts are the potential white emission materials.     

Study on Synthesis,Structure and Properties of Ba0.9 Sr0.1 TiO3: x Eu2 O3 Ceramics

A series of BaTiO₃ solid solutions were synthesized by sol-gel method during different aging time. The effect of aging time on the dielectric properties of BaTiO₃ ceramics was discussed. A series of BaTiO₃: x Eu₂O₃ and Ba_0.9Sr_0.1TiO₃: xEu₂O₃ solid solutions were synthesized by sol-gel method and their properties were investigated. The ceramics obtained were of high dielectric constants at room temperature. The results indicated that the dielectric properties of BaTiO₃ ceramics were improved by doping with Eu₂O₃. The doping of Sr²⁺ resulted in the decrease in T_c and the increase of dielectric constant. The dopant Eu³⁺ not only caused the decrease in T_c, but also caused the broadening of Curie peak.     

Electrospinning synthesis and luminescent properties of Lu2O3:Eu3+ nanofibers

One-dimensional Lu₂O₃:Eu³⁺ nanofibers were prepared by electrospinning followed by high-temperature calcinations. Thermogravimetric and differential thermal analysis, X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, photoluminescent spectra and decay curves were used to characterize the samples. Results showed that samples began to crystallize at ～500 °C and crystallized completely around 1000 °C. The average diameter of nanofibers (1000 °C annealed) was about 55 nm and the particle size of Lu₂O₃:Eu³⁺ increased with increasing annealing temperature. Under ultraviolet excitation, nanofibers exhibited typical red emission of Eu³⁺ in Lu₂O₃. The effect of heat-treatment temperature on luminescent properties of nanofibers was also discussed.     

Intense upconversion luminescence of Er3+/Yb3+ codoped oxyfluoride borosilicate glass ceramics containing Ba2GdF7 nanocrystals

Er3+/Yb3+-codoped transparent oxyfluoride borosilicate glass ceramics containing Ba2GdF7 nanocrystals were prepared and spectroscopic properties of rare earth ions were investigated.Fluoride nanocrystals Ba2GdF7 were successfully precipitated in glass matrix,which was confirmed by X-ray diffraction(XRD)and transmission electron microscopy(TEM)results.In comparison with the as-made precursor,significant enhancement ofupconversion luminescence was observed in the Er3+/Yb3+codoped oxyfluoride glass ceramics,which may be due to the variation of coordination environment around Er3+and Yb3+ions after crystallization.The transition mechanisms of the green and red upconversion luminescence were ascribed to a two-photon process,and that of the blue upconversion luminescence was a three-photon process.     

Ultra-stable Eu3+-doped CsPbCl2Br1 perovskite quantum dots glass for optical temperature sensing

In this work, Eu³⁺-doped CsPbCl₂Br₁ in borosilicate glass was successfully synthesized by the melt quenching annealing technique and crystallization method. This work reports a novel Eu³⁺-doped CsPbCl₂Br₁ perovskite quantum dots (QDs) glass with high sensitivity for optical temperature sensing. The relation of fluorescence intensity ratio (FIR) with the temperature was studied in the temperature range of 80–440 K. Notably, the maximum absolute temperature sensitivity (S_a) and relative temperature sensitivity (S_r) of Eu³⁺-doped CsPbCl₂Br₁ perovskite QDs glass can reach as high as 0.0315 K^–1 and 3.097%/K, respectively. Meanwhile, Eu³⁺-doped CsPbCl₂Br₁ QDs glass demonstrates good water resistance, excellent thermal and cold cycling stability performance. The Eu³⁺-doped QDs glass materials can bring inspiration to the future exploration of rare earth ion-doped QDs glass material on the application of optical temperature sensing in the future.     

Red-Emitting Ga2O3:Eu3+ Powder Derived by Sol-Gel Processing

Ga₂O₃: Eu³⁺ Powder was synthesized by sol-gel method with inorganic salt raw materials, and the crystal structure and luminescent properties were investigated. The structures studied by X-ray diffractionmeter showed that single monoclinism could be obtained using this simple processing. Along with the rise of the calcining temperature, the crystallinity of Ga₂O₃:Eu³⁺ powder increased and the particle size grew larger. The excitation spectra of the powder showed a wide CTS band and typical excitation from Eu³⁺ ion, while the emission spectra had a strongest red emission peak at 613 nm. The excitation and emission intensities changed along with the calcining temperature from 650 to 1050 °C and had an optimal calcining temperature. The excitation and emission intensities also changed along with the doping concentration of Eu³⁺ ion from 0.25% to 4% (atom fraction) and achieve a maximum at a certain concentration which differed for direct Eu³⁺ excitation or CTS excitation. The electroluminescent spectra indicated the typical red emission from Eu³⁺ ion.     

A novel Eu3+-doped phosphor-in-glass for WLEDs and the effect of borophosphate matrix

Phosphor-in-glass(PiG) is a potential color convertor for high power WLEDs.A novel glass matrix with advanced performance is still a challenge.Recently,Eu³⁺ doped glass matrix has attracted much consideration mainly due to its red compensation.A new borophosphate matrix to realize Eu³⁺ red light was designed in the Na₂O-ZnO-P₂O₅-B₂O₃-Eu₂O₃ system.Meanwhile,a series of PiGs composed of different con...     

A comparison research on replacements of Ba2+ by Lu3+ and Ba2+-Si4+ by Lu3+-Al3+ in BaSi2O2N2:Eu phosphors

As a cyan-emitting oxonitridosilicate phosphor,BaSi₂O₂N₂:Eu²⁺can be used as a competent cyan compensator to improve the color rendering index of white light-emitting diodes(WLEDs).However,low luminescence efficiency and poor thermal stability of this type of phosphor seriously suppress its actual application in full-spectrum lighting.The replacements of Ba²⁺by Lu³⁺and Ba²⁺-Si⁴⁺by Lu³⁺-Al³⁺can greatly increase the luminescence intensity and improve the thermal stability at the same time.With Lu³⁺doping,the internal quantum efficiencyηIQE Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺is 24.08%higher than that of Ba_0.97Si₂O₂N₂:0.03 Eu²⁺.After Al³⁺co-doping,theηIQE is further increased by 10.31%compared to Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺.When the temperature rises to 473 K,the luminescence intensity of Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺maintains 62.32%of that at room temperature,which increases by 17.35%in relative to the Ba_0.97Si₂O₂N₂:0.03 Eu²⁺,while the luminescence intensity of Ba_0.925Si_1.97O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺,0.03 Al³⁺keeps 73.87%of the initial value,which increases by18.52%compared to Ba_0.925Si₂O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺.The mechanisms for luminescence and thermal stability improvement are proposed.The Ba_0.925Si_1.97O₂N₂:0.03 Eu²⁺,0.045 Lu³⁺,0.03 Al³⁺cyan phosphor,Y3 Al5 O12:Ce3+yellow phosphor and CaAlSiN3:Eu²⁺red phosphor are mixed thoroughly and coated on a blue LED(450 nm)to assemble a WLED.The WLED demonstrates a color rendering index(Ra)of 97.1 at150 mA,and the R1-R15 values are all above 90.The results indicate that as an effective cyan compensator in WLED,the BaSi₂O₂N₂:Eu²⁺,Lu³⁺,Al³⁺phosphor has great application prospect in the field of full-spectrum lighting.     

The electrical conductivity of some liquids in the system CaF2+CaO+Al2O3

The conductivity of slags in the binary systems CaF₂+Al₂O₃, CaF₂+CaO and the ternary system CaF₂+CaO+Al₂O₃ has been measured, using a four-lead electrode technique at a frequency of 1 kHz. The cell design used ensured that only molybdenum metal was in contact with the slag at high temperature and that the slag was wholly contained in molybdenum. No frequency dispersion could be detected at frequencies between 0.8 to 10 kHz. It is suggested that the formation of complex ions (e.g. AlO₂F₂ ³⁻ and AlOF ₂ ⁻ ) might account for the observed effects in CaF₂+Al₂O₃, CaF₂+CaO+Al₂O₃ liquids as has been previously suggested. an oxide ion clustering mechanism may explain the conductivities found in CaF₂+CaO.     

Effect of rare earths on viscosity and thermal expansion of soda-lime-silicate glass

Viscosity of soda-lime-silicate glass doped with rare earth oxides (Pr₆O₁₁, Eu₂O₃, Yb₂O₃) was investigated by the rotating crucible viscometer, the melting temperature and activation energy for viscous flow of the studied melt were derived on the basis of the Arrhenius Equation, the coefficient of thermal expansion, glass transition temperature and dilatometric softening temperature were also determined with dilatometry, in order to reveal the effects of rare earth elements on the behavior of soda-lime-silicate glass. The results showed that introduction of rare earth oxides decreased the viscosity of soda-lime-silicate glass and melting temperature of corresponding melt, increased coefficient of thermal expansion of soda-lime-silicate glass. The glass transition temperature, dilatometric softening temperature, and melting temperature of soda-lime-silicate glass doped with rare earth oxides increased with increasing cationic field strength of corresponding rare earth ions.     

Spectroscopic properties of Gd2Oa：Dy3＋ nanocrystals

Gd2O3:Dy3+ nanocrystals were synthesized via solvothermal method followed by a subsequent calcination.The samples were characterized by X-ray diffraction(XRD),transmission electron microsopy(TEM),Electronic dispersive X-ray spectroscopy(EDX),photoluminescence(PL)spectrum and decay curves.The effect of the annealing temperature on the crystallinity and particle size was studied;heat treatment improved the crystallinity of as-prepared nanocrystals as well as increased their particle size.The nanocryatals presented monodispersed spherical shape under TEM.Photoluminescence spectra showed that nanocrystal exhibited strong yellow emission corresponding to 4F9/2→6H13/2 transition(573 nm)of Dy3+ under UV light excitation,which broadened with the particle size decreased without structure changed.The theoretical mechanism of luminescence was explored and surface effect was thought to be the main reason.     

Luminescent performance of rare earths doped CaBi2Ta2O9 phosphor

A series of red-emitting phosphors of CaBi₂Ta₂O₉:Pr³⁺ and CaBi₂Ta₂O₉:Eu³⁺ were synthesized by the solid-state reaction method. The crystal structure and photoluminescence properties were investigated by X-ray diffraction (XRD) and photoluminescence spectra. The emission spectra showed that the red emission peaks were located at 622 nm for Pr³⁺ and 615 nm for Eu³⁺, respectively. The optimal doping concentrations for Ca_1?xBi₂Ta₂O₉:xPr³⁺ and Ca_1?yBi₂Ta₂O₉:yEu³⁺ were x=0.02 and y=0.15, respectively. The effect of fluxes (H₃BO₃, NH₄F, CaCl₂ and CaF₂) and charge compensations (Li₂CO₃, Na₂CO₃ and K₂CO₃) on luminescent properties were investigated in detail. It was found that the relative emission intensity of Ca_0.98Bi₂Ta₂O₉:0.02Pr³⁺ with 10 mol.% H₃BO₃ flux was about 2.9 times higher than that of the sample without flux. The relative emission intensity of Ca_0.7Bi₂Ta₂O₉:0.15Eu³⁺, 0.15K⁺ was about the 2.1 times higher than that of Ca_0.85Bi₂Ta₂O₉:0.15Eu³⁺.     

Spectroscopic and structural properties of MgAI204：Nd3＋ nanopowders and ceramics

The structural and spectroscopic properties of MgAl2O4：1%Nd3＋ spinel nanocrystals and ceramics were measured and ana-lyzed. Ceramics were prepared from the above mentioned spinel nanocrystals and undoped commercial spinel powder, using the spark plasma sintering （SPS） method. Properties of the obtained ceramics strongly depended on the SPS conditions. The samples were not homogeneous and possessed defects and pores. The most transparent ceramics had 60% transparency at 1000 nm.     

The solution rate of alumina in CaF2-Al2 O3 slags

The rate of solution of A1₂O₃ in CaF₂ + 30 wt pct A1₂O₃ (at 1518° and 1509°C) and CaF₂ + 20 wt pct A1₂O₃ (at 1500°C) liquids has been determined. The operative process is diffusion-controlled, with an interdiffusion coefficient,D for the process varying between 8.5 and 8.1 x 10^-5 sq cms ^- 1 in the CaF₂ + 30 wt pct A1₂O₃ slags, and 4.0 × 10^-5 sq cms ^- 1 in the CaF₂ + 20 wt pct A1₂O₃ slag. Estimations of the rate at which alumina inclusions would react with these slag during the electroslag processing of steels, indicate that electrode inclusions approaching 100 μ in diam will be dissolved.     

Photoluminescence study of SiO2 coated Eu3+:Y2O3 core-shells under high pressure

Uniform core-shell Eu³⁺:Y₂O₃/SiO₂ spheres were synthesized via precipitation and the Stöber method. The structural transition of core-shell Eu³⁺:Y₂O₃/SiO₂ was studied by using high pressure photoluminescence spectra. With pressure increasing, the emission intensities of ⁵D₀→⁷F_0,1,2 transitions of Eu³⁺ ions decreased and the transition lines showed a red shift. The relative luminescence intensity ratio of ⁵D₀→⁷F₂ to ⁵D₀→⁷F₁ transitions decreased with increasing pressure, indicating lowering asymmetry around Eu³⁺ ions. During compression, structural transformation for cores in the present core-shell Eu³⁺:Y₂O₃/SiO₂ sample from cubic to monoclinic took place at 7.5 GPa, and then the monoclinic structure turned into hexagonal above 15.2 GPa. After the pressure was released, the hexagonal structure transformed back to monoclinic and the monoclinic structure was kept stable to ambient pressure.     

Optical and luminescence characteristics of Eu3+-doped B2O3:SiO2:Y2O3:CaO glasses for visible red laser and scintillation material applications

Europium(Eu~(3+)) doped glasses of chemical compositions(55-x)B_2O_3:10 SiO_2:25 Y_2O_3:10CaO:xEu_2O_3,where x denotes mol% and ranges 0≤ x ≤ 2.5, were synthesized by adopting conventional melt quenching technique, Physical properties like density, molar volume, polaron radius, inter-ionic distance and field strength of the glass samples were investigated to assess the impact of Eu_2O_3. Optical and luminescence properties of the glasses were characterized with optical absorption, photoluminescence,X-ray induced emission spectra, temperature dependence emission spectra and decay times. Judd-Ofelt(JO) intensity parameters(Ω_λ) of the glasses were evaluated based on the absorption spectrum of 0.5 mol%. JO parameters, calculated from absorption spectra with thermal corrections on oscillator strength, were used to evaluate radiative properties such as radiative transition probability(A_R),branching ratio(β_R), stimulated cross section emission(σ) and radiative lifetime(τ_R) for ~5D_0→~7 F_J(J = 0,1,2,3 and 4) transitions. The decay rate of ~5D_0 fluorescent level for all the glass samples was single exponential. Lifetimes of the ~5D_0 level were decreased with increasing concentrations of Eu~(3+)ions from 0.05 mol% to 2.5 mol% which might be due to energy transfer through cross-relaxation in the glasses. The chromaticity coordinates(x, y) were similar for all BSYCaEu glasses and were located at the red region of CIE 1931 color chromaticity diagram. Hence, these results confirm that the Eu~(3+) doped BSYCaEu glasses could be useful for visible red lasers and glass scintillation applications.     

Evaluation of B2O3 as replacement for CaF2 in CaO–Al2O3 based mould flux

In order to develop low fluoride or fluoride free CaO–Al₂O₃ based mould flux for casting high aluminium steel, an investigation was carried out to study the effect of substituting CaF₂ with B₂O₃ on heat transfer and crystallisation behaviour of CaO–Al₂O₃ based mould flux by employing a heat transfer simulator of mould flux and a single hot thermocouple technique. The results showed that addition of CaF₂ promoted heat transfer of CaO–Al₂O₃ based mould flux, which was opposite to the effect of CaF₂ on heat transfer in conventional CaO–SiO₂ based mould flux. Addition of CaF₂ inhibited crystallisation of CaO–Al₂O₃ based mould flux by lowering the start crystallisation temperature and prolonging the incubation time of crystallisation. B₂O₃ showed similar effects to CaF₂ on heat transfer and crystallisation of CaO–Al₂O₃ based mould flux, but its ability to promote heat transfer and suppress crystallisation was stronger than CaF₂. Ca₃B₂O₆ (melting temperature 1480°C) was found as the primary crystalline phase in fluoride free CaO–Al₂O₃ based mould flux compared with the primary crystalline phase Ca₂Al₃O₆F (melting temperature 1507°C) in fluoride bearing (20% CaF₂) CaO–Al₂O₃ based mould flux.