Glasses Tech – Prescription Glasses, Prescription Eyeglasses

The Rayleigh scattering of silicate glasses (M//2O-RO-SiO//2, M: Na and K, R: Mg, Ca, and Zn) was measured. Soda magnesium silicate (NMS) glasses exhibited the smallest scattering intensity. It is comparable with that of soda aluminosilicate (NAS) glass, one of the candidates for use in fabricating ultralow- loss fibers. The scattering intensity decreased with decreasing SiO//2 content, and NMS glasses with 60 mol% of SiO//2 are still stable against crystallization. It is concluded that NMS is a new candidate for ultralow-loss fiber use. (Author abstract) 14 Refs.

Todoroki, Shin-ichi　Sakaguchi, Shigeki

The effect of chlorine on the structure of AlF//3/YF//3-based fluoride glasses was studied by XPS. The changes in the bonding state of cations with increase of chlorine content were all investigated by measuring the composition- dependent changes in the relative concentration and binding energy of related cations. It was proposed that the chlorine replaces the bridging fluorine by which the [AlF//n] and [YF//m] polyhedra are connected and result in the formation of [AlF//n//- //uCl//u] and [YF//m//-//vCl//v] polyhedra. In the low BaCl//2 content region ( less than 6 mol%), as many chlorine as possible attack [AlF//n] and [YF//m] polyhedra, and with the increase of chlorine content, they replace more fluorines in [YF//m] polyhedra, while the number of chlorines in [AlF//n//-//uCl//u] polyhedra remains a low constant value. In the high BaCl//2 content region ( greater than 6 mol%), the chlorines replace more fluorines in the already formed [AlF//n//-//uCl//u] polyhedra and do not attack other [AlF//n] polyhedra, while the composition of [YF//m//- //vCl//v] polyhedra does not change. (Author abstract) 14 Refs.

Zhang, Lipeng　Wang, Paul W.

Sellmeier coefficients are necessary to optimize the design parameters of optical devices. These coefficients ar ecomputed for binary tellurite glasses to findthe chromatic dispersion behavior at any wavelength, particularly at the optical windows of optical fiber communication systems and femtosecond technology. A single-oscillator DiDomenico and Wemple’s dispersion equation is not sufficient to represent accurately the meausred refractive indexes throughout the transmission rnage. As a minimum, a two-pole Sellmeier equation is necessary to represent the data more accurately. Both the average electronic absorption band gap and the lattice absorption freqeuncy, lying in the UV and IR region, respectivley, affect the refractive indexes and their dispersion. Various other optical properites are discussed. A single-oscillator dispersion equation is unable to verify theexistence of zero-dispersion wavelength.

Gorachand Ghosh

Dysprosium-doped glasses were prepared in the system of gallium-based sulfide, tellurite, zirconium-based and indium-based fluorides and their optical properties were studied. From the absorption cross sections of five f-f bands, three Judd-Ofelt parameters, Omega //t (t equals 2, 4, 6), of Dy**3** plus ion were determined. The compositional variation of the Omega //2 value showed the order sulfide greater than tellurite greater than fluorozirconate greater than fluoroindate, whereas the Omega //6 value showed the opposite tendency. Compositional variation of the fluorescence intensity ratio of the (**4F//9/////2 yields **6Hi//1//3/////2)/(**4F//9/////2 yields **6H//1//5///// //2) is explained by the ratio of Omega //2/ Omega //6 of doped Dy**3** plus . The emission probabilities A and the branching ratio beta from **6H//9/////2 and **6F//1//1/////2 levels, which are the doublet initial level of the 1.3 mu m luminescence, were calculated for the glasses, and it was found that both values showed a tendency similar to that of Omega //2 against the glass composition. In the sulfide glass, A was 2.6 multiplied by 10**3 s** minus **1 and beta was 93%, both the highest in all of the glasses investigated. By 1.06 mu m pumping of a Nd:YAG laser, the sulfide glass showed strong 1.3 mu m emission and the lifetime was 25 mu s, resulting in a quantum efficiency of 7%. This value is higher than that of the Pr**3** plus :**1G//4 level in ZBLAN glass with beta equals 60%. (Author abstract) 16 Refs.

Tanabe, Setsuhisa　Hanada, Teiichi　Watanabe, Masayuki　Hayashi, Tetsusuke　Soga, Naohiro

Detailed characteristics of photoinduced surface deposition (PSD) of metallic Ag have been studied using Ag-As-S bulk glasses to reveal the mechanism. The composition dependence of PSD in the Ag//xAs//60-xS//40 (25≤x≤45) system shows that the photosensitivity decreases with a decrease in the Ag content and becomes negligible at x≈25. All the related crystalline materials hardly exhibit the PSD, even if the Ag content is greater than 45 at. %. The size of photodeposited Agparticles and the number per unit area depend on the Ag content and illumination conditions (light intensity, photon energy, and temperature). The PSD phenomenon is induced by light with photon energy higher than the optical band gap, and the photosensitivity shows a maximum at room temperature. PSD can be suppressed by coating over the surface with thin Au film. From these results and other observations it can be suggested that the PSD phenomenon is characteristic of thermodynamically unstable glasses containing excess Ag^+ ions and is a kind of photoelectro-ionic chemical reaction.

Kawaguchi, Takeshi.　Maruno, Shigeo

Physical properties of Ag//2S-As//2S//3 glassy aloys have been studed a a functio of the Ag atomic concentation x. With an increase in x, the opticl-absorptionedge exhibites a red shift, while the steepness of the Urbach tail changes little. In the glasses with x≥15, the elecrtricalcojductivity is voverned by Ag^+ inoic conducto. The ionic consuctivity exponentialy increases erx, and in contrst reh hoel ocnductionvyt hardlychages wit x; however, th activatiion energyies fhe ionic and the hole conductivity are nearly the sme at obur 0.4 eV fr coositons wiot 15≤x≤35. These observations are discussed on the basis of atomic and elctronic structures in Ag//2S-As//2S//3 glasses.

Ohto, M.　Itoh, M.　　

Photoluminescence from Er^3+ or Pr^3+ ion-doped silica or ZBLAN(ZrF//4-BaF//2-LaF//3-AlF//3-NaF) glass, excited by high-energy photos such as excimer laser photons, was investigated mainly through the temperature dependence. When there aretwo emission states whose energy difference is small, as in the case of ^2H//11/2 and ^4S//3/2 in Er^3+ or the ^1I//6/^3P//1 mixing state and ^3P//0 in Pr^3+, the luminescence from the upper state and that from the lower state are found todepend inversely on temperature. This indicates that the thermaolization or thermal equilibrium of electrons between the two emission states occurs.

Yokokawa, T.　Inokuma, H.　

Sodium migration in glasses during electron probe microanalysis is investigated. We observe the change in x-ray emission as a fnction of time andfor various incident electron doses. A specific protocol is used in this study: independently drawn from a multivariate statistical analysis of the data and from an a priori simple model, an exponential decay of the Na signal is clearly established. Thismodel for Na^+ migration is only basedon an electric field with a linear decrease behavior as a function of depth and it acconts for themain expermental results with no evidence of an incubation time prior to ion migration. The electron densities and the fracton of incident electrons remaining trapped into the glass are deduced from an estimate of ion mobility. The maximum electric field values at the coating/glass interface are also given.

Jbara, O.　Cazaux, J.　

The Ag content in Ag-As-S glasses can bve spatially modified by illumination ofvisible light. Optical and thermal studies demosntrate that the Ag-content modification is cuased by Ag^+ ionic migration from the dark to the iluminated region in a sample. The migration can be reversed by changeing the illuminated region. The magnitude of the Ag-content modification is maximal (7 at. %) at a composition of Ag//25As//25S//50. The migration mechanism can be accounted for by assuming diffusion of photoexcited holes, and the composition dependence can be understood on the basis of the Owens’ thermodynamic model.

Norimitsu Yoshida　Keiji Tanaka