Optical properties of silver-doped aluminophosphate glasses

Silver-doped aluminophosphate glasses were prepared by the melt-quenching technique in which silver nanoparticles (NP) of different sizes were embedded upon heat treatment. Optical absorption and photoluminescence spectroscopy were used to study the optical properties of the material before and after thermal processing. Photoluminescence (PL) experiments revealed a broadband emission observed around 420 nm for the non-heat treated samples with a luminescence decay showing a bi-exponential behavior. Temperature dependence PL studies showed a thermal quenching effect on the broadband emission. Our data suggests that the emission is due to single Ag⁺ ions. Optical absorption measurements performed on the heat treated samples allowed for particle size estimation and the evaluation of the thermal stability of the glass system and its attributes as a host for NP inclusion. The nanocomposite showed a dip in the broadband emission of silver ions ascribed to absorption of Ag⁺ ions luminescence by surface plasmons in the silver particles.     

Structure and radiative properties of aluminophosphate glasses

The structure and radiative properties of aluminophosphate glasses in the system K₂O-Al₂O₃-P₂O₅ and BaO-Al₂O₃-P₂O₅ were investigated. The structural changes in glasses with the addition of alumina were investigated by using FTIR spectroscopy and NMR spectroscopy. In the case of the K₂O-Al₂O₃-P₂O₅ glasses, the aluminium atoms were mainly octahedrally coordinated and acted as network modifiers. The decrease in the spontaneous emission rate of K₂O-Al₂O₃-P₂O₅ glasses was due to the tightening of chains in terms of the addition of alumina to the glasses. The increase in effective linewidth was probably due to the increase of end groups in the glasses. In the case of BaO-Al₂O₃-P₂O₅ glasses, the addition of alumina had little effect on the radiative properties, probably due to the small structural change which occurred on its addition.     

Compositional effects on the fracture behaviour of alkali–silicate glasses

The two-point bend strength and the fracture toughness of a series of soda–potassia–silicate and soda–potassia–calcia–silicate glass fibres have been measured. There is a clear variation of mean strength with composition for the soda–potassia–silicate glasses, however, there is much less variation of mean strength with composition for the soda–potassia–calcia–silicate glasses. There is also a greater variation of fracture toughness with composition for the soda–potassia–silicate glasses than for the soda–potassia–calcia–silicate glasses. The mean strength, fracture toughness and inferred flaw sizes for the soda–potassia–calcia–silicate glasses are all less than the equivalent values for the soda–potassia–silicate glasses. These results are related to the structural models and durability of the glasses tested.     

Optical properties of aluminophosphate glasses containing silver, tin, and dysprosium

The spectroscopic properties of a Dy³⁺-doped aluminophosphate glass containing silver and tin were reported. Different oxidation and aggregation states of silver were obtained by varying silver concentration and glass thermal history. The addition of silver and tin at the lowest concentration studied results in Dy³⁺ ions emission under nonresonant UV excitation in connection with the appearance of an excitation band around 270 nm, which is associated to isolated Ag⁺ ions and twofold-coordinated Sn centers. The increase in silver and tin concentration leads to a broadening of aforementioned band and to the presence of charged silver dimers as evidenced by the appearance of an excitation band around 330 nm. The data indicated that light absorption might take place at ionic silver species and twofold-coordinated Sn centers, followed by energy transfer to Dy³⁺ ions. After heat treatment, ionic silver species were reduced to atomic Ag by tin with the subsequent formation of Ag nanoparticles (NPs) inside the dielectric host. A quenching effect in Dy³⁺ ions luminescence was shown with the presence of the Ag NPs, most notably for excitation of ⁶H_15/2 → ⁴F_9/2, ⁴I_15/2, ⁴G_11/2 transitions, which were in resonance with the dipole absorption mode of the particles. The silver NPs were believed to provide radiationless pathways for excitation energy loss in Dy³⁺ ions.     

Cerium doped soda-lime-silicate glasses: effects of silver ion-exchange on optical properties

Effects of silver ion-exchange on optical absorption (OA) and photoluminescence (PL) spectra of a cerium doped soda-lime-silicate glass at room temperature are investigated. The optical spectra are described in terms of the characteristic transitions 4f↔5d originated in Ce³⁺ ions placed mainly in two different sites of the glass network. As Ag⁺ ions are introduced into the cerium doped glass, they are reduced to elementary silver (Ag⁰) which are favoured by the reaction Ce³⁺+Ag⁺→Ce⁴⁺+Ag⁰. Then, the number of Ce³⁺ ions decrease inversely with depth from the surface contrarily to Ce⁴⁺ ions does, and elementary silver diffuses and aggregates to form nanoparticles. As a consequence of these changes, the OA spectra of exchanged samples increase substantially in the UV range and the luminescence decreases significantly. The high sensitivity of PL together with deconvolution analysis of spectra, however, allows us to detect changes in the excitation and emission spectra from the earlier stages of ion-exchange. This indicates that during the ion-exchange we deal with fast processes (much shorter than 1 min). In fact, transmission electron microscopy observations of samples from the glass exchanged for a short time as 1 min at 325°C show the presence of a scanty number of silver nanoparticles, which confirms this point. Furthermore, with increasing the length of time of ion-exchange, PL spectra exhibit a progressive red shift indicative in part of a covalence increment in the oxygen–cerium coordinated bonding. We observe no luminescence from Ag⁺ ions and other silver molecular species in contrast with other preliminary PL studies on silver ion-exchange in soda-lime-silicate glasses free of cerium. The effect is discussed on the basis of a supplementary increase in the number of Ce⁴⁺ ions mainly due to the reaction Ce³⁺+Ag⁺→Ce⁴⁺+Ag⁰, which prevents efficiently the luminescence of the silver centers.     

Thermal and optical properties of the Ga-Ge-Sb-Se glasses

A selected glass composition from the Ga-Ge-Sb-Se has been studied in detail for potential applications in the 8-12 μm region. The Ga₅Sb₁₀Ge₂₅Se₆₀ glass has a high enough glass transition temperature (283 °C), a relatively high refractive index (2.63 at 10 μm) and is very stable towards crystallization. An original purification method is developed to produce high purity glass with good transmission up to 15 μm. This glass is very resistant in normal environmental conditions and even in hot water (60 °C) during 24 h. It may be a good candidate for producing infrared components operating in the mid and far infrared region.     

The influence of CsBr addition on optical and thermal properties of GeGaS glasses doped with erbium

The influence of the addition of CsBr on the optical and thermal properties of GeGaS glass doped with Er has been being investigated. We find that the addition of CsBr into GeGaS glass leads to some improvements in the radiative properties of Er³⁺ ions in this glass system. The GeGaS–CsBr glasses demonstrate much longer radiative lifetimes and stronger photoluminescence for ⁴I_13/2 ?⁴I_15/2^4\hbox{I}_{13/2} \rightarrow{^4\hbox{I}}_{15/2} and ²H_11/2 ?⁴I_15/2 ^2\hbox{H}_{11/2} \rightarrow{^4\hbox{I}}_{15/2} transitions in Er³⁺ ions. Very low Judd-Ofelt parameters and sharp Er³⁺ absorption spectra with multiple peaks suggest the presence of microcrystals. All optical parameters are strongly influenced by the interplay of Ga and CsBr. The glasses studied have been characterized by their basic glass transformation temperatures. The addition of CsBr into GeGaS glass keeping the ratio between CsBr and Ga close to unity is favorable for the incorporation of larger amount of Er. The experimental results are discussed in terms of structural local arrangement induced by CsBr addition.     

Compositional analysis and optical properties of Ag-doped ITO films

ITO and Ag-ITO composite films were deposited on glass substrates by DC magnetron sputtering. Scanning electron microscope images indicated that Ag existed in the form of nanoparticles. X-ray photoelectron spectroscopic analysis illustrated that both Ag doping and heat treatment had obvious influence on the composition and element chemical state of the films. Ag doping dramatically decreased the transmittance of the film. But after being annealed, Ag-ITO films exhibited the high average transmittance of 80-90% in visible wavelength range. By using the spectroscopic ellipsometry optimization, the optical constants were extracted from the transmittance spectra. The results suggested the potential use of Ag-ITO films for antireflection coating system.     

Compositional study and properties characterisation of alkaline earth feldspar glasses and glass-ceramics

Fields in which metastable crystallisation of feldspars may occur as a result of heterogeneous nucleation were defined at 1000° C for the systems BaO-Al₂O₃-SiO₂, SrO-Al₂O₃-SiO₂, and CaO-Al₂O₃-SiO₂. The metastable fields of the above barium and calcium systems differ considerably from the respective primary liquidus fields of celsian and anorthite with the tendency for the stoichiometric compositions to be situated at the centre of the metastable region.Various physical and dielectric properties of the glasses and glass-ceramics of the three systems are presented and compared. High linear thermal expansion, high electrical resistivity, and low loss tangent and dielectric constant characterise these glass-ceramics. One of them (No. 2, table I) has, in addition, high heat resistance and translucency at high temperatures.     

Compositional effect on the crystallization of the cordierite-type glasses

The determination of apparent activation energies for the crystallization of P₂O₅/B₂O₃-containing cordierite-type glasses was conducted by non-isothermal differential thermal analysis (DTA). Glass with excesses both of SiO₂ and Al₂O₃ has a higher activation energy for crystallization. In addition to the main phase of -cordierite, several other phases (farringtonite, clinoenstatite, and forsterite) were detected in the fully crystallized samples by the X-ray powder diffraction technique. The crystallization behavior for the powdered glass was governed by the surface crystallization mechanism, which would not change with composition.     

The effects of the incorporation of lutetium oxide on the density and optical properties of copper phosphate glasses

A range of phosphate glasses containing lutetium was prepared by the melt quenching technique. The densities of annealed and unannealed glass samples, molar volumes and the optical energy gapE _opt of thin blown films of the glasses were determined. It was found that the density and molar volume both increased with increase of Lu₂O₃ content. TheE _opt values showed that they are not sensitive to the incorporation of small amounts of oxides.     

Effects of ultraviolet excitation on the spectroscopic properties of Sm3+ and Tb3+ doped aluminophosphate glasses

Li₂O–BaO–Al₂O₃–La₂O₃–P₂O₅ glasses optically activated with rare earth ions with the 4f⁵, and 4f⁸ electronic configuration (Sm³⁺ and Tb³⁺, respectively) were analyzed by Raman spectroscopy, absorption, excitation photoluminescence, decay curves and temperature dependent photoluminescence. The spectroscopic characteristics of the as-prepared and heat treated samples at temperatures below and above T_g were studied as well as their room temperature photometric properties under ultraviolet excitation. All the doped glasses exhibit typical signatures of the lanthanides in their trivalent charge state. For the samarium doped glass heat treated at 250 °C (<T_g) the Sm²⁺ luminescence was also observed. The analysis of the luminescence efficiency was performed in the interval range of 14 K to room temperature, where the integrated intensity of the luminescence was found to decrease for the Sm³⁺ and Tb³⁺ ions in the studied temperature range. Luminescence decay curves were found to be non-exponential for the ⁴G_5/2 → ⁶H_7/2 and ⁵D₃ → ⁷F₄ transitions of the Sm³⁺ and Tb³⁺ ions, respectively. The results strongly suggest the occurrence of energy transfer processes through cross relaxation phenomena, mediated by dipole–dipole interaction in all the studied samples. The decay of the ⁵D₄ → ⁷F₅ emission of the Tb³⁺ ions was found to be single exponential with a time constant of ∼3.1 ms. Based on the spectroscopic characteristics, models for recombination processes are proposed. The room temperature luminance photometric properties with ultraviolet excitation show that the samarium doped glasses have much lower luminance intensity (around 0.3 Cd/m²) when compared with the 6–7 Cd/m² observed for the terbium doped ones.     

Thermal and optical properties of zinc halotellurite glasses

Zinc halotellurite glasses were studied with respect to the glass transition, softening temperature, thermal expansion, optical energy gap, Urbach energy, density, molar volume, refractive index, polarizability, molar refraction and third order non-linear optical susceptibility. Thermal characteristic were determined using a dilatometry. The optical absorption in the wavelength range (300–3200 nm) was measured. From the absorption edge studies, the values of optical band gap (E _opt) and Urbach energy (ΔE) have been evaluated. Optical parameters viz., color dispersion, dispersion energy, E _d, average oscillator energy, E ₀, and third order non-linear optical susceptibility values are estimated from measuring the refractive index at different wavelength. Results obtained are discussed in terms of the glass structure.     

The optical properties of some borate glasses

The optical properties of potassium borate and sodium borate glasses are presented. The fundamental absorption edge for all the series of glasses were analysed in terms of the theory of Davis and Mott. The position of absorption edge and hence the value of the optical gap, was found to depend on the semiconducting glass composition, and the absorption in these glasses is believed to be associated with indirect transitions. The infrared spectra were recorded and appeared individually similar, which is consistent with the absence of significant structural change between the various glass specimens.     

Compositional effects in the dissolution of multicomponent silicate glasses in aqueous HF solutions

The dissolution rate of multicomponent silicate glasses in a 2.9m aqueous HF solution is investigated as a function of its composition. The glasses studied are composed of SiO₂, B₂O₃, Al₂O₃, CaO, MgO, ZnO, Na₂O and K₂O, covering the compositions of most of the technologically important glasses. Unlike many physical properties, no linear relations are observed between the composition of the glass and its dissolution rate. The dissolution rate of a multicomponent silicate glass is found to be largely determined by two factors: The degree of linkage or connectivity of the silicate network and the concentration of SiO₂ in the glass. It is proposed that the dissolution of the glasses is preceded by the leaching of alkali and alkaline earth components present in the glass, followed by the subsequent dissolution of the leached layer. Probably fluorine species will diffuse into the leached layer to enhance the dissolution rate. Analysis of the activation energy data indicates that in some corrosive glasses the leaching itself becomes rate determining.     

Some studies of the optical properties of tungsten-calcium-tellurite glasses

A range of tungsten tellurite glasses containing calcium was prepared and the densities, optical absorption edges and infrared optical absorption spectra were measured. The optical energy gap is of order 3 eV, somewhat lower than for many oxide-based glasses. It is established that the main absorption bands are related to the bonds in TeO₂ rather than the other components of the glasses.     

Some studies of the optical properties of molybdenum-phosphate glasses

A series of binary MoO₃-P₂O₅ and ternary MoO₃-In₂O₃-P₂O₅ glasses was prepared and their optical properties were investigated. The optical absorption edge of the glasses was measured for specimens in the form of thin blown films. It was found that the fundamental absorption edge of these glasses usually occurs in the ultraviolet region. The linear variation of ()^1/2 with where is the absorption coefficient and is the incident photon energy, is taken as evidence of non-direct interband transitions. The linear dependence of optical gap with molybdenum content indicates that the molybdenum content controls the absorption phenomena in this glassy system. The infrared spectra of all the glasses appeared to be almost the same, indicating that the infrared bands arise primarily from the vibrations of the phosphate and molybdate groups. The structure of molybdenum phosphate glasses is discussed in terms of the formation of mixed phosphate and MoO₄ tetrahedra.     

Compositional effects in the retention of colloids by thermal field-flow fractionation

The retention of polystyrene and silica colloids that have been chemically modified is measured in several aqueous carrier liquids. Retention levels are governed by particle size and composition but are also sensitive to subtle changes in the carrier. Size-based selectivities are higher in aqueous carriers compared to acetonitrile. In aqueous carriers, retention varies dramatically with the nature of the additive, and for a given additive, retention increases with ionic strength, regardless of modifications to the particle surface. The role played by electrostatic effects in retention is studied by varying the ionic strength of the carrier, estimating electrical double layers, determining particle-wall interaction parameters, and calculating the coefficients of mass diffusion and thermal diffusion. Although electrostatic phenomena can affect mass diffusion and particle-wall interactions in carriers of low ionic strength (<10(-3) M), such effects are not great enough to explain the dependence of retention on ionic strength. Therefore, thermal diffusion must be affected directly. Thermal diffusion is found to increase with pH, and at a given pH with the surface tension of the suspended particle. Finally, while the addition of the surfactant FL-70 generally decreases retention, greater retention levels can ultimately be achieved with FL-70 because larger temperature gradients can be used without particle adsorption to the accumulation wall.