Specific Features in the Design of Gradient-Index Elements from Glasses by Ion Exchange

The approaches most universally applied to the design of radial optical gradient-index elements from glasses through ion exchange are analyzed. A new method is proposed for choosing both the optimum initial glass intended for use in ion exchange and the optimum content of exchanging components at the axis and the lateral surface of a cylinder in order to achieve a parabolic distribution of the refractive index. The proposed method is based on the concept of mole-additive modification of the refractive index.     

Influence of diffusion nonlinearity on the characteristics of gradient-index diffractive structures formed in glasses by ion-exchange technique

The influence of the diffusion nonlinearity on the formation of gradient-index diffractive structures by the low-temperature silver ion-exchange method (including electroinduced ion exchange) has been studied for two glasses (light crown type) with the same glass-forming matrix and different alkali compositions. One glass containing only sodium shows the anomalous nonlinearity, and another glass with mixed lithium-sodium composition is characterized by the normal nonlinearity. The silver-sodium exchange in both glasses leads to the same refractive index increments. The simulation of gradient-index diffraction gratings in these glasses demonstrates that the diffusion nonlinearity strongly affects the maximum phase modulations and diffraction efficiency of gradient-index gratings. It is shown that the most efficient diffractive structures can be obtained for glasses with the anomalous diffusion nonlinearity, all other factors being the same.     

Influence of diffusion nonlinearity on the characteristics of gradient-index diffractive structures formed in glasses by ion-exchange technique

The influence of the diffusion nonlinearity on the formation of gradient-index diffractive structures by the low-temperature silver ion-exchange method (including electroinduced ion exchange) has been studied for two glasses (light crown type) with the same glass-forming matrix and different alkali compositions. One glass containing only sodium shows the anomalous nonlinearity, and another glass with mixed lithium-sodium composition is characterized by the normal nonlinearity. The silver-sodium exchange in both glasses leads to the same refractive index increments. The simulation of gradient-index diffraction gratings in these glasses demonstrates that the diffusion nonlinearity strongly affects the maximum phase modulations and diffraction efficiency of gradient-index gratings. It is shown that the most efficient diffractive structures can be obtained for glasses with the anomalous diffusion nonlinearity, all other factors being the same.     

Increase in the refractive index of alkali titanium-hafnium silicate glass upon Na+ (glass)-Li+ (melt) ion exchange

An increase in the refractive index upon ion exchange in the Li₂SO₄ + Li₂MoO₄ salt melt has been studied for glasses of composition (mol %)xLi₂O-(25 -x)Na₂O-15TiO₂-6HfO₂-54SiO₂, wherex = 0, 5, 10, 15, 20, and 25. The ordinary transparent single-layer and two-layer diffusion zones are obtained. In the latter zone, the optically opaque near-surface layer gives way to a deeper optically transparent layer with the refractive index gradient. The opaque layer produced by the low-temperature exchange exhibits a unique structure, which is permeable to melt. An increase in the refractive index as large as 0.055 is achieved for the first time without fracture and crystallization of glass.     

Increase in the refractive index of alkali titanium-hafnium silicate glass upon Na+ (glass)-Li+ (melt) ion exchange

An increase in the refractive index upon ion exchange in the Li₂SO₄ + Li₂MoO₄ salt melt has been studied for glasses of composition (mol %)xLi₂O-(25 -x)Na₂O-15TiO₂-6HfO₂-54SiO₂, wherex = 0, 5, 10, 15, 20, and 25. The ordinary transparent single-layer and two-layer diffusion zones are obtained. In the latter zone, the optically opaque near-surface layer gives way to a deeper optically transparent layer with the refractive index gradient. The opaque layer produced by the low-temperature exchange exhibits a unique structure, which is permeable to melt. An increase in the refractive index as large as 0.055 is achieved for the first time without fracture and crystallization of glass.     

离子交换对硼硅酸盐平板玻璃表面组成及性能的影响

研究用低温离子交换法增强硼硅酸盐平板玻璃.以熔融KNO3作为离子交换源,分别加入少量KOH,KF和锑酸钾(K2H2Sb2O72H2O)添加剂,在玻璃转变温度以下对硼硅酸盐平板玻璃进行K -Na 离子交换处理.利用电子探针研究了离子交换前后玻璃的表面组成变化;测定了样品的显微硬度、抗折强度和透过率.研究了添加剂种类与玻璃抗折强度之间的关系.研究结果表明:经K -Na 离子交换处理后硼硅酸盐玻璃表面K 浓度增加,交换深度可达30μm.经K -Na 离子交换后硼硅酸盐平板玻璃的强度提高,其抗折强度约为交换前的3倍.     

KOH对离子交换增强硼硅酸盐玻璃性能的影响

采用低温型离子交换法对硼硅酸盐玻璃进行增强。以掺有添加剂KOH的KNO3混合熔盐作为离子交换源,研究KOH掺入量对硼硅酸盐玻璃抗折强度、显微硬度和透过率的影响。采用扫描电子显微镜(SEM)观察离子交换后试样的表面形貌和结构。研究结果表明:KNO3熔盐中的WKOH/WKNO3为0.5时,硼硅酸盐玻璃的抗折强度和显微硬度都取得了最大值。     

A new method for recording images in glasses

A new method for recording images in alkali silicate glasses preliminarily subjected to ion exchange in a salt melt containing silver ions is proposed. The method is based on the process of glass poling followed by heat treatment in a hydrogen atmosphere. The use of the electrode (anode) with a relief surface pattern results in the formation of an amplitude imprint (image) of this pattern under the glass surface. A trial glass sample with the amplitude pattern of the surface relief of a coin has been produced.     

Thermal history and its implications: A case study for ion exchange

Glasses containing monovalent species can be chemically strengthened by the replacement of smaller ions in the glass with larger external ions in the near glass surface. This type of ion exchange puts glass surface under high compressive stress (CS). Glass mainly fails from tension with the presence of surface flaws. Chemical strengthening can change the stress at the flaw tip from tension to compression and further stop the flaw from propagating. Glass damage resistance is therefore significantly improved. For the same glass composition, glass thermal histories can affect the magnitude and depth of the CS generated during ion exchange. In this study, the impact of thermal history on glass physical properties and ion exchange attributes in one alkali-containing glass formed by fusion draw process was investigated. Multiple thermal treatments were done to rewrite the glass thermal histories. Glass density, refractive index, and ion-exchange properties as a function of the thermal treatment were studied. It is concluded that ion exchange-related properties change dramatically with the glass thermal history.     

Development of Porous Antireflective Films on Borosilicate Glasses

Experiments were conducted to characterize the development of gradient-index antireflective (GIAR) films formed on a phase-separated alkali borosilicate glass. Solution chemistry, secondary-ion mass spectrometry, Auger electron spectroscopy, weight-loss, scanning electron microscopy, and specific surface area analyses were used to evaluate a proposed model for film formation. The results suggest that the film-forming process is more complicated than proposed. For near-optimum heat trcatments, the film-formation acid treatment was virtually nonselective; only for much longer than optimum annealing times was selectivity evident. The graded-index films may result from precipitation of dissolved glass. The analyses were complicated by major compositional variations existing in the as-received glass.     

Spectrum of Volume Relaxation Times in B2O3

Time-index of refraction isotherms were measured for B₂O₃ glass starting from both a high and a low temperature in the transformation region. The equilibrium index values at each temperature, obtained from both types of approach curve, were identical. As in the case of the density values, the equilibrium refractive index curve as a function of temperature for this glass is not a straight line. The two-relaxation-times (crossover) model was applied to B₂O₃ glass and fitted the data as well as it did in previous experiments with borosilicate crown and GeO₂ glasses. The reverse crossover which was predicted by the model was experimentally confirmed with the B₂O₃ glass. The spectrum of relaxation times narrowed with decreasing temperature, indicating approach to another region of single relaxation associated with the low-temperature Arrhenius region. The relaxation times for the low-temperature crossover agreed well with those from the high-temperature curves, indicating complete linearity in the experiments. The spectrum of relaxation times was slightly asymmetrical at constant pressure and very asymmetrical at constant volume.     

Effect of halogen on imprinting gradient refractive index microstructure in GeS2–Ga2S3–NaX (X=F,Cl, Br,I) glasses for broadband infrared diffraction gratings

Chalcohalide glasses with a gradient refractive index (GRIN) microstructure were imprinted by microthermal poling for realizing diffractive optical elements covering the visible to middle-infrared wavelength range. The effect of halogen ions on the saturation poling voltage (U), surface profile, diffraction pattern, optical transmittance, GRIN microstructure, and structural rearrangement of poled glass is investigated. An effective imprinting formation region for a GRIN microstructure based on the U and glass composition is observed under fixed poling time and temperature. The onset U (60 V–150 V) and activation energy of mobile cations (0.449 eV–0.533 eV) decreases with the atomic number of the halogen from F to I, but the saturation diffractive order (8th to 11th levels) and phase difference (~0.08λ to 0.18λ) increases accordingly. The onset U and activation energy decrease with the deformability of the glass network and radius of the halogen ions. The phase difference and saturation diffractive orders decrease with the proportion and electronegativity of interval halogen atoms in the glass network. Thus, chalcohalide glasses with GRIN microstructures can be tailored by adjusting the type of halogen ions for realizing various diffraction optical elements.     

IR and XPS Studies on the Surface Structure of Poled ZnO–TeO2 Glasses with Second-Order Nonlinearity

The effect of thermal/electrical poling on the surface structure of 30ZnO·70TeO₂ glass has been investigated by means of IR reflectance and X-ray photoelectron spectroscopy (XPS). All the poled glasses exhibit a common characteristic that the second-order nonlinearity is induced preferentially in an anode-side surface region. The reflectance from the anode-side glass surface at around 635 cm^{− 1} assignable to the vibrational mode of the Te–O_ax bond, where ax stands for the axial position of the TeO₄ trigonal bipyramid, is smaller in comparison with both as-annealed and cathode-side surfaces. The XPS analysis of the anode-side surface shows a depletion of Zn²⁺ ions and penetration of Na⁺ ions from the borosilicate glass which was placed between the sample and the anode during poling. These results suggest that the poling brings about both the breaking of the tellurite glass network and compositional changes at the anode-side surface below which the second-order nonlinearity is preferentially induced.     

Ion Depletion of Glass at a Blocking Anode: II, Properties of Ion-Depleted Glasses

The application of an electric field to an ion-conducting glass at high temperatures will cause depletion of mobile ions beneath a blocking anode. The present study extends the investigation of ion depletion to several types of ion-conducting glass and presents new data for the physical and chemical properties of depleted surfaces. Ion-scattering spectrometry and electron microprobe analysis show that all positive monovalent and divalent ions are removed from the vicinity of the anode. The less mobile ion species are observed to pile up beneath the depleted region. Experimental data indicate that the removal of ions from the vicinity of the anode creates a microporous region that densifies at a rate determined by glass composition, temperature, and voltage. Ion-depleted surfaces display a lower refractive index and an increased electrical resistivity compared to untreated glass. Ion depletion also imparts an enhanced chemical durability to glass surfaces and increases the breaking strength of some glasses.     

Boron Coordination in Rapidly Cooled and in Annealed Aluminum Borosilicate Glass Fibers

The fraction of four-coordinated boron was observed to increase from 10% in a rapidly cooled aluminum borosilicate glass fiber to 16% in the same fiber after it was annealed; the refractive index also increased. The index of the annealed fiber agreed with that of the bulk glass. Crystallization was not observed in the annealed fiber. It is concluded that boron coordination is temperature dependent and associated with structural relaxation.     

Relation Between Refractive Index and Density of a Glass at Constant Temperature

Data are presented on the changes in the room-temperature refractive index and density of a borosilicate crown glass produced by different heat-treatments. Measurements on a large number of samples with widely varying thermal history show that the refractive index is a single-valued function of the density. The increase in refractive index for a given density change is smaller than that calculated by the Lorentz-Lorenz theory; the apparent contribution of the induced polarization to the local electric field is very small. This may be due to a reduction in the ionic polarizabilities that accompany the density increase; alternatively, the Lorentz-Lorenz form of the theory may not be valid in solid materials such as glass. Data of other investigators are shown to agree with the data reported here.     

Model for Ion-Exchanged Waveguides in Glass

An analytical model describing refractive index profiles in ion-exchanged glass waveguides is presented. Polarizability, volume, and stress-state changes are accounted for. Index distribution is given in terms of known or measurable physical parameters. Model predictions compare favorably with experimental results of field-assisted ion-exchanged waveguides fabricated in 7740 borosilicate glass. Experimental characterization of the index changes includes prism coupling, microprobe, and photoelastic measurements.     

Optical properties of bismuth tellurite based glass

A series of binary tellurite based glasses (Bi(2)O(3))(x) (TeO(2))(100-) (x) was prepared by melt quenching method. The density, molar volume and refractive index increase when bismuth ions Bi(3+) increase, this is due to the increased polarization of the ions Bi(3+) and the enhanced formation of non-bridging oxygen (NBO). The Fourier transform infrared spectroscopy (FTIR) results show the bonding of the glass sample and the optical band gap, E(opt) decreases while the refractive index increases when the ion Bi(3+) content increases.     

Chemical durability of borosilicate pharmaceutical glasses: Mixed alkaline earth effect with varying [MgO]/[CaO] ratio

Glass for pharmaceutical packaging requires high chemical durability for the safe storage and distribution of newly developed medicines. In borosilicate pharmaceutical glasses which typically contain a mixture of different modifier ions (alkali or alkaline earth), the dependence of the chemical durability on alkaline earth oxide concentrations is not well understood. Here, we have designed a series of borosilicate glasses with systematic substitutions of CaO with MgO while keeping their total concentrations at 13 mol% and a fixed Na₂O concentration of 12.7 mol%. We used these glasses to investigate the influence of R = [MgO]/([MgO] + [CaO]) on the resistance to aqueous corrosion at 80°C for 40 days. It was found that this type of borosilicate glass undergoes both leaching of modifier ions through an ion exchange process and etching of the glass network, leading to dissolution of the glass surface. Based on the concentration analysis of the Si and B species dissolved into the solution phase, the dissolved layer thickness was found to increase from ~100 to ~170 nm as R increases from 0 to 1. The depth profiling analysis of the glasses retrieved from the solution showed that the concentration of modifier ions (Na⁺, Ca²⁺, and Mg²⁺) at the interface between the solution and the corroded glass surface decreased to around 40%–60% of the corresponding bulk concentrations, regardless of R and the leaching of modifier cations resulted in a silica-rich layer in the surface. The leaching of Ca²⁺ and Mg²⁺ ions occurred within ~50 and <25 nm, respectively, from the glass surface and this thickness was not a strong function of R. The leaching of Na⁺ ions varied monotonically; the thickness of the Na⁺ depletion layer increased from ~100 nm at R = 0 to ~200 nm at R = 1. Vibrational spectroscopy analysis suggested that the partial depletion of the ions may have caused some degree of the network re-arrangement or re-polymerization in the corroded layer. Overall, these results suggested that for the borosilicate glass, replacing [CaO] with [MgO] deteriorates the chemical durability in aqueous solution.     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.