S.N. Houde-Walter

Local structure of Er3+ in multicomponent glasses

Erbium environments in several multicomponent glasses are investigated using X-ray absorption fine structure spectroscopy on the Er LIII-edge. Glass hosts studied include aluminosilicate, fluorosilicate, phosphosilicate, alkali phosphate, fluoride, and another multicomponent silicate glass. The Er–O separation is found to vary only slightly between 2.21 and 2.25 A. The first shell coordination number is dependent on glass host ranging from 6.3 nearest neighbor anions in the aluminosilicate glass to 10.0 in the fluoride host. The Debye–Waller factor for the first shell is also host dependent. It ranges from 0.021A2 in the phosphate hosts to 0.033 A2 in the aluminosilicate glass. While Er–Er correlations are observed in the crystalline Er2O3 standard, no evidence of molecular or short-range clustering of Er3+ ions is found in the glasses. Photoluminescence spectra are also presented for each of the glass hosts examined.

Hydroxyl-contents and hydroxyl-related concentration quenching in erbium-doped aluminophosphate, aluminosilicate and fluorosilicate glasses

In this paper, we present a study of concentration quenching in Er3+-doped aluminophosphate, aluminosilicate and fluorosilicate glass hosts. Results of experimental measurements of the excited state lifetime in these glasses, as a function of the Er3+ concentration, are reported. A simulation is presented which explains the concentration-dependent reduction in Er3+ excited state lifetime using a model based on quenching by hydroxyl (OH) impurities present in the glass. In addition, 1H nuclear magnetic resonance (NMR) spectroscopy is used to make direct measurements of OH contents in rare-earth (RE) free analog glasses. The OH contents are related to spectral features in the infrared absorption spectroscopy in the range 2600–3800 cm−1. The correlation between infrared spectral features and OH content allows a comparison of the estimated number of quenched Er3+ ions to OH content in the Er3+-doped glasses.

Chemical structure and the mixed mobile ion effect in silver-for-sodium ion exchange in silicate glasses

The relationship between chemical structure and ion transport in silver-for-sodium ion exchange in the endpoints of a series of sodium aluminosilicate glasses is examined. It is shown that the non-bridging oxygen (NBO) content of the glass has a major impact on both the local environments of the mobile cations and the mixed mobile ion effect (MMIE). X-ray absorption fine structure studies of the local environments of the mobile cations are used to help formulate a structural picture of ion exchange, in which interactions between the mobile cations affect ion transport rates. Studies of the diffusion coefficient using energy dispersive microanalysis and the modified quasi-chemical (MQC) diffusion coefficient are used to obtain quantitative values for MMIE. Parameter fits of the MQC diffusion coefficient to experimentally obtained values are used to extract self-diffusion coefficients, excess interaction energies and cation-cation coordination numbers. It is found that the NBO-rich glass has the highest excess interaction energy and exhibits the greatest MMIE, consistent with the structural model.

Modeling ion-exchanged glass photonics: the modified quasi-chemical diffusion coefficient

Abstract A new description of concentration-dependent ion exchange is presented. A three-dimensional, quasi-chemical approximation is used to estimate the chemical potentials of the exchanging cations. The diffusion coefficient is then expressed as a function of the self-diffusion coefficients, excess interaction energy and cation-cation coordination. The modified quasichemical description results in excellent fits to experimentally determined concentration-dependent diffusion coefficients. It is shown to be useful for modeling the strong concentration-dependence of ion exchange as used in the development of glasses for micro- and gradient-index optics.

Temperature dependence of silver-sodium interdiffusion in micro-optic glasses

Abstract The variation of the concentration-dependent diffusion process with ion exchange temperature from 280°C to 400°C has been investigated in two boro-aluminosilicate glasses suitable for micro-optic applications. Silver dopant concentration profiles are measured using energy dispersive X-ray spectroscopy and converted to concentration dependence using an analytical formulation of the Boltzmann-Matano analysis. Extensive error analysis of the Boltzmann-Matano method is presented. While the overall interdiffusion rates vary strongly with temperature, the temperature variation of the concentration dependence does not exceed experimental error. Temperature dependencies of Ag and Na self-diffusion coefficients are also presented. The activation energies for Ag and Na are both approximately 0.72 eV in these glasses.

Ionic mobility in an ion exchanged silver—sodium boroaluminosilicate glass for micro-optics applications

Abstract Several samples of a sodium-containing boroaluminosilcate glass were ion exchanged to equilibrium from mixed silver and sodium nitrate salt liquids. The resulting glasses had homogeneous compositions, but each contained different relative amounts of Ag and Na. Silver and Na radioactive-tracer diffusion coefficients were then measured in these glasses as a function of host composition. The measured Na and Ag tracer coefficients vary by factors of only two and ten over the full composition range. The interdiffusion coefficient is measured by applying Boltzmann—Matano analysis to energy-dispersive X-ray spectroscopy composition profiles. We show that the mobility contribution to the interdiffusion coefficient can be approximated by using constant tracer diffusion coefficients. Further, the thermodynamic contribution is larger than in samples of furnace-melt, double-alkali glasses. These results cannot be attributed to the thermal history of these glasses.

Relaxation behavior of silver–sodium interdiffusion in a boroaluminosilicate glass

Abstract It is shown that interdiffusion of silver into a well-annealed sodium boroaluminosilicate glass can induce significant relaxation of the host glass at temperatures well below the transition temperature, Tg. The relaxation is manifest as a time-dependent interdiffusion coefficient which is shown to increase as the time of diffusion varies from 1.5 to 30 h. The presence of Ag is required for the observed relaxation; differential scanning calorimeter (DSC) scans and 22Na radioisotope-tracer diffusions indicate that the base glass is fully annealed before interdiffusion. An estimate of the characteristic relaxation time is given. Inclusion of the time-dependence is required to predict refractive index distributions within tolerance allowed for micro-optics applications, as shown by simulation.

Structural factors in silver-induced relaxation in aluminosilicate glasses

Abstract The effect of the duration of diffusion is investigated in boroaluminosilicate and aluminosilicate glasses with varying non-bridging oxygen (NBO) contents. Silver/sodium interdiffusion coefficients are measured using energy-dispersive X-ray spectroscopy (EDX) and the Boltzmann–Matano method in glasses that have been ion-exchanged for 1.5, 5, 30, 75 and 120 h at 350 °C. The interdiffusion coefficient is strongly time-dependent for the NBO-poor glass, but changes negligibly in the case of the NBO-rich glass. Radioactive tracer diffusion coefficients are also measured for the NBO-poor glass using 110m Ag and 22 Na radioisotopes. The tracer coefficients are also time-dependent. We show that the cross-coefficients, which are used to relate tracer and interdiffusion in this glass, vanish for long diffusion times. This behavior is interpreted in terms of changes in the local cation environments induced by the presence of the dopant cation, and relaxation of the associated intermediate range structure in the glass.

New rare-earth hosts: OH in laser glasses

Furnace-melt, multi-component glasses are used to produce dense gain media for waveguide and micro-chip lasers. The compositional flexibility is often accompanied by elevated water contents, which can lead to hydroxyl (OH) quenching. OH quenching can significantly shorten excited state lifetimes, even at low pump powers. It therefore becomes important to know and control the OH content of laser glasses. While a simple relation between infrared vibration spectra and OH contents exists for vitreous silica, we show that this relation does not apply to multicomponent glasses. Instead, we present a self-consistent calculation to determine an order- of-magnitude estimate of the number of quenched rare-earth (RE) ions in multi-component glasses. Infra-red absorption spectra and fluorescence lifetimes are required. This method gives an accurate prediction of quench-shortened fluorescent lifetimes in a wide variety of host glasses.

Ion-exchanged Er3+/Yb3+ glass waveguide lasers in silicate glasses

Waveguide lasers and amplifiers in glasses codoped with Er3+ and Yb3+ are promising candidates for compact multifunctional devices operating near 1.5 μm.