Structural,optical and non-linear investigation of Eu<Superscript>3+</Superscript>: Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> sol-gel glass

Optical absorption and fluorescence spectra of Eu³⁺ ions in Al(NO₃)₃-SiO₂ sol-gel glass have been investigated using the Judd- Ofelt theory. JO intensity parameters (ω _λ ) and subsequent radiative properties for⁵ D ₀ ↔⁷ F _1,2,4,6 transitions are determined. The lifetime (τ_r) of⁵ D ₀ state is computed and along with JO parameters are compared with their corresponding values in other glasses prepared by conventional technique. A structural analysis, using IR and XRD spectra and non- linear parametrization of the silica gel glass is carried out. The study reveals the glass to be a very good third order non- linear amorphous optical material.     

Effects of F− on the optical and spectroscopic properties of Yb3+/Al3+-co-doped silica glass

Yb³⁺/Al³⁺-co-doped silica glasses with different F⁻ content were prepared in this work by sol–gel method combined with high temperature sintering. XRF, FTIR and XPS methods were used to confirm the presence of F⁻. The effects of F⁻ on the optical and spectroscopic properties of these glasses have been investigated. It is worth to notice that the F⁻/Si⁴⁺ mass ratio equal to 9% is a significant value showing a real change in the variation trends of numerous following parameters: refractive index, UV absorption edge, absorption and emission cross sections, scalar crystal-field N_J and fluorescent lifetimes. Furthermore, introduction of F⁻ can adjust the refractive index of Yb³⁺/Al³⁺-co-doped silica glass and it is useful for large mode area (LMA) fibers.     

Spectroscopic properties of Er doped and Er, Nd codoped fluoride glasses under simulated sunlight illumination

We investigated the fluorescence characteristics of Er codoped Nd doped ZBLAN glasses proposed for solar pumped fiber laser (SPFL) under simulated sunlight. Er is used as a sensitizer because it absorbs a part of the ultraviolet and visible light where is no absorption of Nd. Under simulated sunlight illumination, Er singly doped fluoride glass displayed four emission bands with peaks at 550, 848, 977 and 1533 nm attributed to the ⁴S_3/2-⁴I_15/2, ⁴S_3/2-⁴I_13/2, ⁴I_11/2-⁴I_15/2 and ⁴I_13/2-⁴I_15/2 electronic transitions of Er, respectively. The quantum efficiency measurement was carried out using an integrating sphere and under the simulated sunlight excitation showed a maximum of 73% for 0.5 mol.% of ErF₃ in ZBLAN glass. In Nd, Er codoped fluoride glass, the 1.05 μm emission of Nd was observed under 380 nm excitation what supposes the energy transfer from Er to Nd in ZBLAN glasses as Nd has no absorption at the wavelength. Er, Nd codoped fluoride glasses are promising as a sensitized laser media for solar pumped fiber lasers.     

Spectroscopic studies of Cu<Superscript>2+</Superscript> ions in sol-gel derived silica matrix

The Cu²⁺ ion doped silica gel matrices in monolithic shape were prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS). The absorption, transmittance and fluorescence spectra of the gel matrices heat treated at different temperatures were monitored. The loss of water and hydroxyl group from silica network changes the optical properties of the Cu²⁺ ions in the host, noted by the change in colour of monolith and spectral characteristics. The pronounced blue shift observed (700–900 nm to 600–850 nm) for the broad band of the absorption spectra of the samples heated up to 700°C is attributed to the ligand field splitting and partial removal of hydroxyl group from the silica matrices. The results indicate broadband filtering effects of the samples in the wavelength region 400–600 nm. Absorption and fluorescence spectra of the glass matrices heated to 1000°C confirms the conversion of Cu²⁺ ion to Cu⁺ ion.     

New transparent Er-doped oxyfluoride tellurite glass ceramic with improved near infrared and up-conversion fluorescence properties

Transparent glass ceramics have been obtained by nucleation and growth of Y₂Te₆O₁₅ or Er₂Te₅O₁₃ cubic phase in a new Er³⁺-doped oxyfluoride tellurite glass. Effect of heat treatment on absorption spectra, luminescence and up-conversion properties in the oxyfluoride tellurite glass has been investigated. With heat treatment the ultraviolet absorption edge red shifted evidently for the oxyfluoride telluride glass. The near infrared emission that corresponds to Er³⁺:⁴I_13/2 → ⁴I_15/2 can be significantly enhanced after heat treatment. Under 980 nm LD pumping, red and green up-conversion intensity of Er³⁺ in the glass ceramic can be observed much stronger than that in the base glass.     

UV–vis spectroscopic studies of CaF2 photo-thermo-refractive glass

A photo-thermo-refractive glass based on the system Na₂O/K₂O/CaO/CaF₂/Al₂O₃/ZnO/SiO₂ doped with Ag₂O, CeO₂, SnO₂, Sb₂O₃ and KBr was investigated. This glass undergoes a permanent refractive index change after UV irradiation and subsequent two step heat treatment at temperatures above Tg. This is due to the formation of Ag metal clusters which act as nucleation centers for CaF₂ crystallization. Oxidation of Ce³⁺ by UV light is the initial reaction and acts as photosensitizer in the glass. The UV–vis absorption spectra during this photo-induced crystallization process were measured. The spectral components that form the absorption spectra of cerium were studied in detail by a band separation with Gaussian functions. Deconvolution of the cerium absorption bands shows an envelope of five spectral components for the trivalent cerium due to the 4f-5d transitions and two spectral components for the tetravalent cerium caused by charge transfer transitions. The effect of different dopants and melting conditions on the photo-thermal process were studied to investigate the influence of glass technology on the photoprocess.     

Fabrication of high-purity silica glass through the WSPA-sol-gel process

High-purity and large-size silica glass was prepared by a wet process silica and pH adjustment (WSPA)-sol-gel process which involved the following steps: (1) colloidal silica synthesis through the hydrolysis reaction of TEOS catalysed by ammonia solution; (2) sol preparation through the hydrolysis reaction of TEOS by hydrochloric acid; (3) mixing the colloidal silica and sol solution; (4) adjusting the pH values of the mixed solution to 4–6; (5) gelling; (6) drying to a dry gel; (7) heat treatment of the gel to collapse the pores, finally to become a silica glass. The purity of the derived silica glass was examined in relation to the metallic impurities and -OH impurities. The relation between ultraviolet absorption of silica glass and metallic impurities was investigated. Ti addition to the silica glass gave a strong absorption at 200 m, for which the ultraviolet absorption coefficient, , was found to be 1.57×10⁴ l mol^–1 cm^–1. The effects of the properties of colloidal silica on the -OH concentration and also the relations between the sintering conditions and residual -OH concentration in silica glass were examined. Using colloidal silica with a large particle size and heat treatment in vacuum resulted in a silica glass with a low concentration of residual -OH.     

Effect of hydroxyl content on the physical properties of calcium metaphosphate glasses

The hydroxyl (OH) content of calcium metaphosphate glasses has been controlled in the range 50–800 ppm by melting calcium dihydrogen phosphate in air, under vacuum and with fluoride addition. Density, refractive index and glass transition temperature of the glasses increase with decrease in OH content while the coefficient of thermal expansion remains almost unchanged. With gradual decrease in OH, the UV cutoff initially shifts towards shorter and finally towards longer wavelengths. IR spectroscopic study shows that the OH groups exist exclusively in the hydrogen bonded states. Correlations of the glass properties with OH content have been explained in terms of structural rearrangement leading to the change in P-O bond length and O-P-O/P-O-P bond angles of the PO₄ tetrahedral units of (PO ₃ ⁻ ) _n chains. These changes are caused due to conversion of non-bridging oxygens (NBOs) of the H-bonded OH groups into bridging oxygens (BOs) during progress of dehydroxylation.     

The 1.53 μm spectroscopic properties of Er3+/Ce3+/Yb3+ tri-doped tellurite glasses containing silver nanoparticles

The metallic silver nanoparticles (NPs) was introduced into the Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glasses with composition TeO₂–ZnO–La₂O₃ to improve the 1.53 μm band fluorescence. The UV/Vis/NIR absorption spectra, 1.53 μm band fluorescence spectra, fluorescence lifetimes, X-ray diffraction (XRD) curves, differential scanning calorimeter (DSC) curves and transmission electron microscopy (TEM) image of tri-doped tellurite glasses were measured, together with the Judd–Ofelt intensity parameters, emission cross-sections, absorption cross-sections and radiative quantum efficiencies were calculated to investigate the effects of silver NPs on the 1.53 μm band spectroscopic properties of Er³⁺ ions, structural nature and thermal stability of glass hosts. It is shown that Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glasses can emit intense 1.53 μm band fluorescence through the combined energy transfer (ET) processes from Yb³⁺ to Er³⁺ ions and Er³⁺ to Ce³⁺ ions under the 980 nm excitation. At the same time, the introduction of an appropriate amount of silver NPs can further improve the 1.53 μm band fluorescence owing to the enhanced local electric field effect induced by localized surface Plasmon resonance (LSPR) of silver NPs and the possible energy transfer from silver NPs to Er³⁺ ions, and an improvement by about 120% of fluorescence intensity is found in the studied Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glass containing 0.5 mol% amount of silver NPs with average diameter of ∼15 nm. The energy transfer mechanisms from Yb³⁺ to Er³⁺ ions and Er³⁺ to Ce³⁺ ions were also quantitatively investigated by calculating energy transfer microparameters and phonon contribution ratios. Furthermore, the thermal stability of glass host increases slightly with the introduction of silver NPs while the glass structure maintains the amorphous nature. The results indicate that the prepared Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glass with an appropriate amount of silver NPs is an excellent gain medium applied for 1.53 μm band EDFA pumped with a 980 nm laser diode (LD).     

Light emission at 2 μm from Ho-Tm-Yb doped silicate glasses

The 2.0 μm emission properties and thermal stability of Yb-Tm-Ho triply-doped silicate glass are investigated. The characteristic temperatures, absorption spectrum and fluorescence spectra of the glasses are measured. Intensive emission near 2.0 μm is observed upon excitation at 980 nm and the corresponding mechanisms are discussed. Based on the measured absorption spectra, the absorption and emission cross sections, the Judd-Ofelt parameters and radiative properties are calculated and discussed. The predicted spontaneous transition probability for Ho³⁺:⁵I₇ → ⁵I₈ transition in silicate glass is 58.05 s⁻¹. The results indicate that the energy transfer in Yb³⁺ → Tm³⁺, Yb³⁺ → Ho³⁺, Tm³⁺ → Ho³⁺ is efficient and the Yb-Tm-Ho triply-doped silicate glass is a promising 2.0 μm laser glass material.     

Synthesis of Er<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> : Yb<Subscript>3+</Subscript> doped sol-gel derived silica glass and studies on their optical properties

Er₃₊ and Er₃₊ : Yb₃₊ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol-gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er₃₊ doped samples clearly revealed the absorption due to Er₃₊ ions. On the other hand Yb₃₊ : Er₃₊ doped samples showed enhanced absorption due to² F _7/2 →² F _5/2 transition. The absorption and emission cross-section for² F _7/2 ↔² F _5/2 of Yb³⁺ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm⁻¹. The 960 cm^-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.     

Effect of Calcium on Nd:GdVO4 single crystal

The Ca_0.08Gd_0.92VO₄ crystal and Nd-doped Ca_0.08Gd_0.92VO₄ crystals were grown by the Czochralski method; the lattice parameters of the crystals were determined by XRD. The results showed that substituting Nd³⁺ caused an increase in lattice parameter; the segregation coefficient of Nd³⁺ ions in the crystal is lower than that of Nd:GdVO₄ crystal; the absorption spectra, fluorescence spectra, absorption cross-section and the emission cross-section of the Nd:Ca_0.08Gd_0.92VO₄ crystal were investigated at room temperature; furthermore, the Raman performance of Ca_0.08Gd_0.92VO₄ crystal was improved.     

Synthesis of mesoporous SiO2 glass by a novel chemical method

A novel five-step method for fabricating mesoporous SiO₂ glass was described in this paper, which consists of: (1) formation of colloidal suspension of Zn(OH)₂, (2) synthesis of silica sol, (3) mixture of Zn(OH)₂ colloidal suspension and silica sol to form nano-ZnO embedded precursor glass, (4) annealing of the precursor glass, and (5) treating nano-ZnO embedded glass with HCl to obtain the mesoporous glass. The mesostructure of the glass was investigated by X-ray diffraction (XRD), field emission scanning electron microscope (SEM), and BET surface area analysis. The average pore size distribution is in the range of 3.7 nm, and the surface area is as high as 496.5 m²/g.     

Eu3+ probe ion for rare-earth dopant site structure in sol–gel derived LiYF4 oxyfluoride glass–ceramic

Sol–gel route using metal alkoxides and trifluoroacetic acid as precursors has been used to prepare oxyfluoride glass–ceramic containing Eu³⁺-doped LiYF₄ nanocrystals of about tens of nm size embedded in a silica matrix through controlled crystallization at higher temperatures of the xerogel. Photoluminescence spectra and decay curves recorded in the Eu³⁺-doped LiYF₄ polycrystalline pellet and glass ceramic have been discussed using group-theoretical arguments. In the glass–ceramic Eu³⁺ ions are embedded dominantly inside the LiYF₄ nanocrystals most probably as Eu–O center and/or dimer centers in low symmetry (C_2v) sites; oxygen ions were incorporated in their neighborhood during the glass ceramization.     

Preparation of a water-soluble oligo-(p-phenylene vinylene) embedded silica composite glass through a novel sol–gel process

We describe an improved sol–gel process to prepare a water-soluble oligo-(p-phenylene vinylene) (ws-OPV) doped silica composite glass. The addition of Li₂CO₃ to neutralize the composite sol and solvent extraction with cyclohexane reduces the processing time from several weeks for traditional sol–gel process to several days. The crack-free ws-OPV doped silica composite glass with the low volume shrinkage can be obtained by this process. The choice of ws-OPV ensures the possibility of this modified process. The results of fluorescence spectra indicate that the adjustable and improved emission of composite glass can be achieved, and the photostability is much better, all of which make such composite glasses of more practical significance.     

Spectra and energy levels of Nd3+(4f3) in stoichiometric NdP5O14

We report a detailed crystal-field splitting analysis of the 13 lowest-energy multiplet manifolds, ^2S+1L_J, of Nd³⁺(4f³) in stoichiometric NdP₅O₁₄. The observed manifold splittings were determined by analyzing the absorption spectra between 550 and 1750 nm and the fluorescence spectra between 800 and 1400 nm at temperatures between 8 K and room temperature. The spectra are remarkably sharp given the high concentration of Nd (28.91 wt%) in the stoichiometric crystal. The number of transitions to and from individual multiplet manifolds is consistent with Nd³⁺ ions occupying sites, reported earlier to be of low symmetry (C₁). Sixty experimental energy (Stark) levels associated with the 13 manifolds are compared to a crystal-field splitting calculation in which the observed-to-calculated rms deviation is 6.8 cm⁻¹.     

Role of tin as a reducing agent in iron containing heat absorbing soda-magnesia-lime-silica glass

The role of tin as a reducing agent in a 18Na₂O·2MgOO·8CaOO·72SiO₂ glass containing a definite amount of total, ΣFe = [Fe²⁺] + [Fe³⁺], was investigated with different concentrations of total tin, ΣSn = [Sn²⁺] + [Sn⁴⁺], by absorption spectra of iron ions in the optical range 300–1200 nm recorded on a JASCO-7800 spectrophotometer. The single broad absorption band for Fe²⁺ ion was marked at 1055 nm in the near infrared region and a narrow weak band for Fe³⁺ ion at its λ_max at around 380 nm was observed in the silicate glass. The proportion of ferrous iron was found to increase in the glass in the beginning with the addition of tin up to 0 788% Σ Sn and then it approached a maxima with 1182% Σ Sn. Further addition of tin was found to be futile for the constant iron concentration of 0–875% for achieving higher [Fe²⁺]/[Fe³⁺] ratio for maximum heat absorption due to Fe²⁺ ion in the glass. The mechanism of the process was discussed on the basis of Sn²⁺/Sn⁴⁺ and Fe²⁺/Fe³⁺ mutual redox interaction in the molten glass at 1400°C. The suitable limit of tin was suggested to be 0.788 ≤x ≤ 1.182% by wt for 0.875% of total iron for getting maximum ferrous ion in the glass.     

Fluorescence properties of Eu3+-doped alumino silicate glasses

Alumino silicate glasses of a very broad range of molar compositions doped with 1 ⋅ 10²⁰ Eu³⁺ cm⁻³ (about 0.2 mol% Eu₂O₃) were prepared. As network modifier oxides Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, ZnO, PbO, Y₂O₃ and La₂O₃ have been used. All glasses show relatively broad fluorescence excitation and emission spectra. For most glasses only a weak effect of the glass composition on the excitation and emission spectra is observed. Although the glasses should be structurally similar, notable differences are found for the fluorescence lifetimes. These increase steadily with decreasing mean atomic weight, decreasing refractive index and decreasing optical basicity of the glasses, which may be explained by local field effects. An exception from this rule are the strontium, barium and potassium containing glasses, which show significantly increased fluorescence lifetimes despite of their high refractive index, optical basicity and molecular weight. The non mono-exponential fluorescence decay curves as well as the fluorescence spectra indicate a massive change in the local surroundings of the doped rare earth ions for these glasses.     

Raman spectroscopic investigation of sodium borosilicate glass structure

Raman spectra of sodium borosilicate glasses with a wide range of Na₂O/B₂O₃ ratios were systematically measured. Variations of the spectra with glass composition were studied to interpret the implied distribution of Na⁺ ions between silicate and borate units. When Na₂O/B₂O₃ is less than 1, all Na⁺ ions are associated with borate units as indicated by the absence of the 1100 cm⁻¹ band of Si-O⁻ non-bridging bond stretching. For the (1−x)Na₂O · SiO₂ ·xB₂O₃ glass withx≦0.4 the peak-height ratio of the 950 cm⁻¹ band to the 1080 cm⁻¹ band was used to analyse semiquantitatively the distribution of the Na⁺ ions between silicate and borate units. Sodium ions are divided between silicate and borate units approximately in proportion to the amount of SiO₂ and B₂O₃ present in these glasses. Some of the high sodium content glasses were crystallized and their spectra were compared with the bulk glass spectra. The distribution of Na⁺ ions in the glass was quite different from their distribution after crystallization. Spectra of high silica glasses that had been heat-treated for phase separation indicated exclusion of borate units from the silica network and the formation of borate groups. For high boron content glasses, no change was observed on heat treatment. Raman bands due to borate groups seem to be little affected by their environments. Also affiliated with the Department of Geosciences.