Hydroxyl Impurities Research Articles

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 Er 3+-doped aluminophosphate, aluminosilicate and fluorosilicate glass hosts. Results of experimental measurements of the excited state lifetime in these glasses, as a function of the Er 3+ concentration, are reported. A simulation is presented which explains the concentration-dependent reduction in Er 3+ 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 Er 3+ ions to OH content in the Er 3+-doped glasses.

Luminescence of OH − impurities in crystals of rubidium halides

Photoluminescence of crystals of RbCl, RbBr, RbI doped with OH − ions was systematically investigated as a function of dopant concentration and temperature. The emission spectra show the occurrence in all three systems of three emission bands due to hydroxyl impurities, whose features are in good agreement with previous findings in potassium halides and partial data on RbCl and RbBr. The luminescence of OH − ions in RbI was identified and characterized for the first time. Emission bands caused by other kinds of oxygen-related centers, such as O 2 − molecular ions and perhaps O 2- ions, were revealed.

Magnetite film growth at 30 °C on organic monomolecular layer, mimicking bacterial magnetosome synthesis

At 30 °C magnetite (Fe3O4) films were successfully grown, ∼5 μm in thickness, by flowing for 20 h a mixed gas of O2/N2=1/2000 on lipid monomolecular layers of arachic acid spread on an aqueous solution of FeCl2. The ordered array of the OH groups of the lipid layer stimulated the nucleation and growth of the Fe3O4 films, similar to that proposed for the bacterial magnetosome (Fe3O4 crystals) synthesis in which the OH groups on the cytoplasmic membrane stimulates the surface growth of Fe3O4. The Fe3O4 films obtained in this study contained a small amount of ferric hydroxyl impurity phases of α-FeOOH and γ-FeOOH, as shown by x-ray and Mössbauer analyses.

Synthesis & Characterization of Optically-Active Lanthanide-Doped Hybrid Inorganic-Organic Systems

ABSTRACTThe materials chemistry of sol-gel-derived inorganic-organic molecular composites offers significant potential for molecular-level systems design. One focus in this arena is the chemical design and microstructural engineering of optically-active systems. We report the generation of rare-earth-doped inorganic-organic hybrids, based on a bridged polysilsesquioxane architecture. Derived from lanthanide precursors such as Erbium isopropoxide, which we co-condense with the requisite silsesquioxane monomer, these systems exhibit significant optical activity. In experiments on hybrids doped with Erbium, we conclusively demonstrate strong fluorescence at wavelengths in the vicinity of 1540 nm, from stimulation with 488 nm radiation. We discuss materials-driven impacts of the bridged-silsesquioxane architecture on system complexities arising from the solution sol-gel route which would affect fluorescence efficiencies and luminescence levels, such as hydroxyl impurities and clustering-effects.

Reversible Kinetics and Thermodynamics of the Homopolymerization of l-Lactide with 2-Ethylhexanoic Acid Tin(II) Salt

The reversible kinetics of l-lactide bulk polymerization with tin(II) ethylhexanoate was determined over a wide range of temperatures, 130−220 °C, and monomer to initiator molar ratios, 1000−80 000. Both polymerization and depolymerization are accurately described by a reversible model with a propagation term that is first order in monomer and catalyst. The activation energy of propagation is 70.9 ± 1.5 kJ mol-1. The enthalpy, entropy, and ceiling temperature of polymerization are −23.3 ± 1.5 kJ mol-1, −22.0 ± 3.2 J mol-1 K-1, and 786 ± 87 °C, respectively. Crystallization increases the propagation rate and decreases the apparent monomer equilibrium in proportion to the degree of crystallinity. Natural hydroxyl impurities stoichiometrically control the polymer molecular weight but do not significantly affect the propagation rate.

An Investigation of Radiation Damage Induced by Hydroxyl and Oxygen Impurities In BaF2 Crystal

ABSTRACTThe radiation effect in hydrolyzed BaF2 was investigated through tile changes in their optical absorption and EPR spectra before and after γ-irradiation. The resulti demonstrated that hydroxyl and oxygen can be easily introduced into BaF2by means of a hydrolysis, the most likely modes are OH— ions substituting for fluorine and O2– ions substituting for fluorine associated with charge-compensating fluorine vacancies O2– — F+. Combining with the Hartree-Fock-Slater local-density discrete variational (HFS-Xα-DV) cluster calculation on some possible defects related to hydrogen and oxygen impurities, we propose that the radiation damage observed in hydrolyzedBaF2 can be explained in terms of OH— and O2– — F+ dissociation through a radiolysis.

Preparation of D 2O-treated sol-gel silica preform and OD absorption bands at IR and near-IR region

A hydroxyl impurity in sol-gel silica glass is replaced by a deuteroxyl group to study the contributions of the OD absorption to fiber losses in the near-IR region. The hydroxyl group is successfully substituted with the deuteroxyl group by deuterium oxide vapor treatment on the gel at 800°C for 30 min. An IR absorption band due to the OD fundamental vibration is observed at 3700 nm. In the near-IR region, the third overtone, a combination of the third overtone with the SiO2 fundamental vibration, and the fourth overtone are observed at 955, 900, and 775 nm, respectively. The residual deutroxyl content tends to a decrease with increasing germanium content and with decreasing heating rate during the densification process. The contribution of these absorption bands to the fiber losses at 630 nm is negligible and at 800 nm is

X-Ray Induced Optical Absorption in Densified Silica Glass in the UV Region

ABSTRACTX-ray induced optical absorption has been studied on silica glasses densified by hot isostatic pressing. Density of the glass increases up to about 1% in proportion to the operating pressure. Two main absorption bands centered at 5.8eV(215nm) and 4.8eV(260nm) are induced both in the densified and undensified glasses under the irradiation of X-rays at room temperature. The 5.8eV band is enhanced with the increase in density for the glass with low-OH content(<˜200ppm), but is decreased slightly for the glass with high-OH content(>˜200ppm). On the other hand, the 4.8eV band decreases with the increase in density irrespective of OH content, and reaches at a constant value above the densification of about 0.5%. It is found that these absorption bands originate in point defects in the glass and that the densification improves the optical durability of the glass against X-rays when hydroxyl impurities are contained in the glass.

Optical Properties and Structure of Defects in Silica Glass

This paper reviews what is known about the structures and optical properties of point defects in silica glass and other amorphous forms of SiO2. The available structural information derives mainly from the results of electron spin resonance (ESR) spectrometry-a method which is directly applicable only to the subclass of defects which are paramagnetic. The intrinsic paramagnetic centers so far identified by ESR include E' centers (≡Si·), nonbridging-oxygen hole centers (≡Si-O·), peroxy radicals (≡Si-O-O·), and self-trapped holes. Examples of intrinsic diamagnetic defects believed to occur in silica in include neutral oxygen vacancies (≡Si-Si≡), two-coordinated silicone (O-Si-O-), and peroxy linkages (≡Si-O-O-Si≡). The most common extrinsic defects are associated with hydroxyl and chloride impurities. Radiolytically induced H0 and H2 play important roles in the post-irradiation growth and decay kinetics of defects in glasses containing_??_100ppm OH. A compendium of ESR/optical correlations taken from the literature points to the most likely origins of many defect-related optical absorption bands in the visible, ultraviolet and vacuumultraviolet spectral regions. Others of these bands have been ascribed to interstitial O2, O3 and Cl2 molecules on the basis of similarities of their spectral positions and widths to those of the corresponding species in the gas phase.

Changes in the optical absorption of CaF 2, SrF 2 and BaF 2 induced by thermal annealing in different atmospheres

Modifications induced in the optical absorption spectra of CaF 2, SrF 2 and BaF 2 single crystals by annealing at 900 °C in different atmospheres have been studied. No bulk effects appear if the annealings are performed in dry oxygen or dry nitrogen atmospheres. By annealing in water containing atmospheres both oxygen and hydroxyl impurities seem to be incorporated into the bulk samples. Surface defects associated with oxygen and carbonate ions are also observed after some of the annealing treatments.

Thermoluminescence and hydroxyl defects associated with broad-band infra red absorption in synthetic quartz

A study has been made of thermoluminescence from synthetic quartz with varying hydroxyl impurity concentrations up to approximately 300 H/106 Si which are associated with a “broad-band” IR absorption in the range 2600–3700 cm−1. These hydroxyl defects are known to be important in the hydrolytic weakening of quartz. We have found only minor differences in the glow curves of unheated crystals but significant intensity increases when “wet” crystals are heated sufficiently to cause bubble formation. It would seem that the electron traps are unaffected by the bubble formation, but the electron/luminescence centre radiative recombination probability is increased.

Nd:YAG quantum efficiency and related radiative properties

Measured quantum efficiencies of ten different Nd:YAG crystals show a variation from 0.47 to 0.87. In phototropic crystals, the quantum efficiency can be degraded by color center formation or improved by bleaching. Color center bleaching occurs by oxidation, using a high-temperature reactive atmosphere process to control crystal defects related to hydroxyl impurities. Ion-ion and ion-lattice interaction effects are examined for further evidence of Nd/sup 3+/ fluorescence quenching centers. Fluorescence rates, nonequivalent crystal field (NCF) effects, line broadening, Nd/sup +3/ lattice-defect interactions, and their temperature dependences are studied. Nd/sup 3+/ site perturbations occur in all crystal samples. Five NCF Nd/sup 3+/ sites show 6 cm/sup -1/ site-to-site Stark level shifts at liquid helium temperatures. Smaller scale shifts are characteristic of particular samples. While the crystals examined show individual differences, only hydroxyl-related coloration provides specific evidence of quenching centers. >

Mn2+centres in hydrolysed SrF2:Mn

Changes in the optical absorption and electron paramagnetic resonance (EPR) spectra of manganese-doped SrF2 single crystals under thermal treatments in different atmospheres have been studied. The influence of the presence of water vapour in the annealing atmosphere has also been analysed. No changes were induced by thermal treatments at temperatures below 700 degrees C. By annealing up to 900 degrees C in a dry atmosphere, only a decrease in the Mn2+ cubic signal was observed. Anneals in water-containing atmospheres between 700 and 900 degrees C modify the EPR as well as the optical absorption of the samples. The EPR spectra of two new Mn2+ centres were analysed and values for their spin-Hamiltonian parameters are given. The role played by oxygen and/or hydroxyl impurities, which were incorporated into the bulk after the hydrolysis process, in the structure of these defects is discussed. The results show that Mn2+ modifies the hydrolysis processes in SrF2 under annealing above 700 degrees C in a wet atmosphere and suggest that manganese ions act as a trap for oxygen and hydroxyl impurities.

Single-mode fiber waveguides with losses below 1 dB/km

The modified chemical vapor deposition (MCVD) technology was used in fabrication of single-mode fiber waveguides from a quartz glass. The core was doped with germanium dioxide and the cladding deposited on it was doped with phosphorus oxide and with fluorine. The minimum losses were 0.6 dB/km at the wavelength of 1.3 µ and 0.35 dB/km at 1.5 µ. The excess losses were attributed to the presence of hydroxyl impurity groups and also due to variation of the fiber parameters along their length.

Hydroxyl impurity effects in YAG (Y3Al5O12)

Evidence is reported of 1020 cm−3 hydroxyl impurity density affecting crystal fields and color center formations in YAG and Nd:YAG. Also reported is a high-temperature reactive atmosphere process to control H bonding and to bleach coloration. Absorption by O–H⋅⋅⋅O and O–D⋅⋅⋅O transitions in the 3–4 μm spectral region was observed in different crystals. Two independent O–H⋅⋅⋅O lines, both with weak satellites, were detected at 3340 and 3374 cm−1. H-bonding sites were assigned by (i) frequency dependence on O2−–O2− distance and (ii) Nd:YAG nonequivalent crystal field effects seen in Nd3+ fluorescence. H+ concentrations 1020 cm−3 were derived from these results. Bonding site relative densities also varied with the different crystals observed. Reactive atmosphere processing (RAP) could cause H+ or D+ to be coordinated into or out of crystals, concomitant with color center bleaching. Color center formations were dissociated by surface reaction with I2 + H2O or I2 + O2 reactive atmosphere at temperatures in the range of 1350–1880 °C. The RAP effect was to produce bulk crystal electronic transfers related to hydrogen in the crystal metal–oxide system. However, photoinduced coloration was again possible. Intense coloration also resulted from vacuum heating, causing an H2O effluent. The evidence indicated YAG and Nd:YAG contained a high concentration of largely mobile H+ affecting O− -center coloration and influencing crystal fields by bound-small polaron formations.

Effects of compression direction on the plasticity and rheology of hydrolytically weakened synthetic quartz crystals at atmospheric pressure

A hydrothermally grown synthetic quartz crystal with 370±60 ppm hydroxyl impurity was cut into right rectangular prisms in eight crystallographic orientations. We compressed the prisms under constant axial force corresponding to a uniaxial stress of 140.0±0.5 MPa, and temperatures of 510° and 750°C. All but one of the samples sustained permanent axial strains of 2–3%. We established the operating slip systems from specimen shape change, slip bands and dislocation etch pits on polished surfaces, crystallographic orientation changes, stress optical features in thin sections, and transmission electron microscopy. The observed creep behavior and plasticity divided the samples into three groups: (1) Crystals compressed at 45° to [0001] and [ ] and those compressed ⊥( ) and ⊥( ) deformed principally by slip parallel to [0001]. Creep rates were relatively high and were not strongly sensitive to test temperature. Dislocation arrays approximately parallel to ( ) are common. Dislocation loops are elongate parallel to [0001], indicating that the edge segments were more mobile than the screw segments. (2) The second group of samples were loaded normal to [0001] in three orientations: ⊥( ), ⊥( ), and at 45° to ( ). These samples deformed primarily by { } 〈a〉 slip with some evidence for secondary slip on the other systems. They were more creep resistant than the first group and displayed a much higher sensitivity of creep rate to test temperature. Dislocation loops are very elongate parallel to [0001], indicating that the screw dislocation segments were much more mobile than the edge segments. (3) A sample compressed parallel to [0001] at 750°C crept at a barely detectable rate (∼10−9 s−1) and no optical scale slip features were observed. These results confirm our earlier work on one orientation each from groups 1 and 2, which indicated a strong creep anisotropy for this same crystal. This creep anisotropy parallels a remarkably similar anisotropy in the diffusivity of impurities in quartz, suggesting a causal relationship between impurity diffusion and creep associated with hydrolytic weakening.Appendix Tables A1‐A5 are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document B84‐004; $2.50. Payment must accompany order.

New method for the optimization of thermoluminescence sensitivity in LiF:Mg,Ti

Glow curve shape and thermoluminescence (TL) sensitivity in LiF:Mg,Ti single crystals have been studied as a function of Mg2+ and Ti3+ concentrations. A detailed method for TL optimization is presented, along with a simplified scheme which relies on the ratio of peak 5 height to peak 4 height (or ratio of peak 5 to peak 3) and the height of peak 3. In addition, the role of hydroxyl (OH−) impurities has been investigated and it has been found that some Mg ions are removed from the TL process by forming magnesium-hydroxyl complexes Mg(OH)n. This may explain prior discrepancies in Mg and Ti concentrations for optimum TL sensitivity.

Mechanism and parameters of the quenching of luminescence of rare-earth ions by hydroxyl impurity groups in laser phosphate glass

An experimental study was made of the parameters and mechanism of the quenching of the luminescence of rare-earth ions by hydroxyl groups. This was done for nine transitions. The permissible concentration of the OH groups were found for laser glasses intended for different applications.

Ionic transport in the BeF 2CsF glass system

A conductivity anomaly has been observed for the purified BeF 2CsF glass system. Initial additions of CsF to vitreous BeF 2 decrease the conductivity σ by two orders of magnitude. The minimum conductivity is at 3 mol% CsF whereupon further additions of the CsF modifier gradually increase σ. The vitreous BeF 2 and 44.0 Kcal/mol at the conductivity minima. A d.c. electrolysis technique verified that fluorine transport is the dominant transport mode at all CsF concentration. A model for conduction is proposed based upon two competing fluorine transport mechanisms: (1) an anti-Frenkel defect mechanism at low CsF concentrations, and (2) a classical non-bridging fluorine transport mechanism at higher CsF concentrations. The model shows fluorine transport to be highly dependent on hydroxyl impurities.

Positions of hydrogen impurities in BaTiO3 crystals

IR absorption of BaTiO3 melt-grown single crystals shows very clearly the presence of hydroxyl impurities. Nevertheless, no OH centers could be identified by EPR. Possible reasons for the EPR inactivity may be the presence of trivalent cation impurities, or a very short lifetime of the VOH centers.