Nonisothermal crystallization kinetics and microstructure evolution of calcium lanthanum metaborate glass

This paper reports results on the crystallization kinetics of 35.5CaO-7.25La(2)O(3)-57.25B(2)O(3) glass under nonisothermal conditions based on the studies carried out from the differential thermal analysis upon using various well-established models. The crystalline phases formed during the optimized ceramization process have been confirmed from the X-ray diffraction. The activation energies of the first (formation of CaLaB(7)O(13)) and second (formation of LaBO(3)) crystallization events have been estimated using the conventional methods of Kissinger, Augis-Bennett, Ozawa, and Matusita, and the results are found to be in good agreement with each other. The Avrami exponents that are determined by these models for the crystallization of CaLaB(7)O(13) and LaBO(3) are found to be in the range of (1.81-2.35) and (4.03-4.65), respectively. This indicates that the formation of CaLaB(7)O(13) is dominated by a surface crystallization, whereas LaBO(3) is formed by three-dimensional bulk crystallization with an increased rate of nucleation. This observation is further validated by microstructural investigation, which shows the formation of CaLaB(7)O(13) phase as a surface layer and a bulk crystallization of LaBO(3) in optimally ceramized samples

Recovery of Acrylic Acid Using Calcium Peroxide Nanoparticles: Thermodynamics and Continuous Column Study

The thermodynamic parameters (DGº, DHº, and DSº) for adsorption of acrylic acid on CaO2 nanoparticle were estimated in the temperature range of 300.15 – 313.15 K, which helps to evaluate the feasibility of adsorption process, nature of adsorption process, and affinity of adsorbent toward solute molecule. A dynamic adsorption study in a fixed-bed column was performed using CaO2 nanoparticle for the recovery of acrylic acid from aqueous stream. The breakthrough curves of adsorption system were obtained for different process variables, such as initial acrylic acid concentration (2882–7206 mg L–1), flow rate (5–9 mL min–1), and bed height (10–20 cm). The bed-depth service time model, Thomas model, Yoon-Nelson model, and deactivation kinetic model were applied to the experimental data to predict the column performance. The data were in good agreement with the deactivation kinetic model. The presented results may be useful for the design of adsorption system using nanoparticles, which can be further extended to other systems. This work is licensed under a Creative Commons Attribution 4.0 International License

Enhanced Blue Emission from Transparent Oxyfluoride Glass Ceramics Containing Pr3+:BaF2 Nano-crystals

Transparent glass ceramics containing Pr3+:BaF2 nano-crystals in chemical composition of SiO2–BaF2–K2CO3–La2O3-Sb2O3 oxyfluoride glass systems have been prepared from melt quenching and with subsequent heat-treatment method. Luminescence and structural properties of these materials have been evaluated and the results are reported. Rietveld analysis of X-ray diffraction (XRD) patterns and investigation of transmission electron microscopy (TEM) confirmed the presence of BaF2 nano-crystals dispersed in the heat treated glass matrices. Measured UV-Vis-NIR absorption spectra have exhibited nine bands of the transitions 3H4 3P2, (1I6, 3P1), 3P0, 1D2, 1G4, 3F3,3F2, 3H6 and 3H5 from all the samples with non-degenerated 1I6 and 3P1 levels in the glass ceramics. The photoluminescence spectra show an enhancement in the intensities upon ceramization indicating the incorporation of Pr3+ ions in BaF2 nano-crystals which possess low phonon energy (346 cm-1). This has further been corroborated from the observation of a significant 3-fold increase in the relative intensity ratio of blue (3P0 3H4) to red (1D2 3H4, 3P0 3H6)emissions from glass-ceramics compared with the glass. It is due to a significant decrease of multiphonon non-radiative relaxation from 3P0 to 1D2 level of Pr3+ in glass ceramics. Time resolved spectra exhibit 3P0 level decays faster than 1D2 level

Concentration quenched luminescence and energy transfer analysis of Nd(3+) ion doped Ba-Al-metaphosphate laser glasses

This paper reports the dopant ion (Nd(3+)) concentration effects on its luminescence properties in a new glass system based on barium-alumino-metaphosphates. Amongst the studied concentrations range of 0.276-13.31x10(20) ions/cm(3), the glass with 2.879x10(20) ions/cm(3) (1 mol%) Nd(3+) concentration shows intense NIR emission from (4)F(3/2) excited state, followed by a decrease in emission intensity for further increase in Nd(3+) ion concentration. The observed luminescence quenching is ascribed to Nd(3+) self-quenching through the donor-donor migration assisted cross-relaxation mechanism. The microscopic energy transfer parameters for donor-acceptor energy transfer, C (DA), and donor-donor energy migration, C (DD), have been obtained from the theoretical fittings to experimental decay curves and the spectral overlap model respectively. The C (DD) parameters (x10(-39) cm(6)/sec) are found to be about three orders greater than that of C (DA) (x10(-42) cm(6)/sec) for Nd(3+) self-quenching in this host, demonstrating that the excitation energy migration among donors is due to the hopping mechanism. The energy transfer micoparameters obtained in the present study are comparable to the values reported for commercially available laser glasses LHG-8 and Q-98

Sensitized red luminescence from Bi(3+) co-doped Eu(3+): ZnO-B2O(3) glasses

Photoluminescence properties of Bi(3+) co-doped Eu(3+) containing zinc borate glasses have been investigated and the results are reported here. Bright red emission due to a dominant electric dipole transition (5)D(0) -> (7)F(2) of the Eu(3+) ions has been observed from these glasses. The nature of Stark components from the measured fluorescence transitions of Eu(3+) ions reveal that the rare earth ions could take the lattice sites of C, or lower point symmetry in the zinc borate glass hosts. The significant enhancement of Eu(3+) emission intensity by 346nm excitation ((1)S(0)->(3)P(1), of Bi(3+) ions) elucidates the sensitization effect of co-dopant. The energy transfer mechanism between sensitizer (Bi(3+)) and activator (Eu(3+)) ions has been explained. (C) 2009 Elsevier B.V. All rights reserved

Efficient non-resonant energy transfer in Nd3+ - Yb3+ codoped Ba-Al-metaphosphate glasses

An efficient Nd3+ ® Yb3+ energy transfer in a new series of alkali-free bariumalumino-metaphosphate glasses with a transfer efficiency reaching up to 95% has been reported here. It is due to the effective phonon assistance arising with the excellent matching of the present host phonon energy with the energy mismatch between Nd3+ (4F3/2) and Yb3+ (2F5/2) excited levels. The energy transfer microparameters for Nd3+ ® Yb3+ forward and back energy transfer are estimated from the spectral data analysis. A parameter, ET (= Nd Yb DA C − / Nd Nd DA C − ) is proposed as a quantitative measure of sensitization ability per unit loss of the donor. The parameter is found to be highest for the presently reported barium-alumino-metaphosphate glasses

Luminescence properties of dual valence Eu doped nano-crystalline BaF2 embedded glass-ceramics and observation of Eu2+ -> Eu3+ energy transfer

Europium doped glass ceramics containing BaF2 nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF2 nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm-1 has been demonstrated from the emission spectra of Eu3+ ions showing the transitions from upper excitation states 5DJ (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu3+) ions to divalent (Eu2+) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu2+ to Eu3+ ion by radiative trapping or reabsorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu3+ to Eu2+ under normal air atmospheric condition has been observed in a BaF2 containing oxyfluoride glass-ceramics system

Time resolved spectra and energy transfer analysis of Nd3+-Yb3+-Er3+ triply-doped Ba-Al-metaphosphate glasses for an eye safe emission (1.54 μm)

This paper reports on the development and systematic analysis of energy transfer mechanisms in Nd3+-Yb3+-Er3+ co-doped new series of barium-alumino-metaphosphate glasses. The time resolved fluorescence spectra of Nd3+ in triply doped Ba-Almetaphosaphte glasses have revealed that, Yb3+ ions could function as quite efficient bridge for an energy transfer between Nd3+ and Er3+ ions. As a result, a fourfold emission enhancement at 1.54 μm of Er3+ ions has been achieved through an excitation of 4F5/2 level of Nd3+ at 806 nm for the glass having 3 mol% Yb3+ with an energy transfer efficiency reaching up to 94%. Decay of donor (Nd3+) ion fluorescence has been analyzed based on theoretical models such as Inokuti-Hirayama, Burshtein (migration) and Yokota-Tanimoto (diffusion) and corresponding energy transfer parameters have been discussed. Primarily, electrostatic dipole-dipole (s ~ 6) interactions are found to be responsible for the occurrence of energy transfer process in theses glasses

Western Indian Ocean marine and terrestrial records of climate variability: a review and new concepts on land-ocean interactions since AD 1660

We examine the relationship between three tropical and two subtropical western Indian Ocean coral oxygen isotope time series to surface air temperatures (SAT) and rainfall over India, tropical East Africa and southeast Africa. We review established relationships, provide new concepts with regard to distinct rainfall seasons, and mean annual temperatures. Tropical corals are coherent with SAT over western India and East Africa at interannual and multidecadal periodicities. The subtropical corals correlate with Southeast African SAT at periodicities of 16–30 years. The relationship between the coral records and land rainfall is more complex. Running correlations suggest varying strength of interannual teleconnections between the tropical coral oxygen isotope records and rainfall over equatorial East Africa. The relationship with rainfall over India changed in the 1970s. The subtropical oxygen isotope records are coherent with South African rainfall at interdecadal periodicities. Paleoclimatological reconstructions of land rainfall and SAT reveal that the inferred relationships generally hold during the last 350 years. Thus, the Indian Ocean corals prove invaluable for investigating land–ocean interactions during past centuries

2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 460 (2009): 1113-1116, doi:10.1038/nature08233.Northern Hemisphere surface temperature reconstructions suggest that the late twentieth century was warmer than any other time during the past 500 years and possibly any time during the past 1,300 years. These temperature reconstructions are based largely on terrestrial records from extra-tropical or highelevation sites; however, global average surface temperature changes closely follow those of the global tropics, which are 75% ocean. In particular, the tropical Indo- Pacific warm pool (IPWP) represents a major heat reservoir that both influences global atmospheric circulation and responds to remote northern latitude forcings. Here we present a decadally resolved continuous sea surface temperature (SST) reconstruction from the IPWP that spans the past two millennia and overlaps the instrumental record, enabling both a direct comparison of proxy data to the instrumental record and an evaluation of past changes in the context of twentieth century trends. Our record from the Makassar Strait, Indonesia, exhibits trends that are similar to a recent Northern Hemisphere temperature reconstruction. Reconstructed SST was, however, within error of modern values during the Medieval Warm Period from about AD 1000 to AD 1250, towards the end of the Medieval Warm Period. SSTs during the Little Ice Age (approximately ad 1550–1850) were variable, and 0.5 to 1°C colder than modern values during the coldest intervals. A companion reconstruction of δ18O of sea water—a sea surface salinity and hydrology indicator— indicates a tight coupling with the East Asian monsoon system and remote control of IPWP hydrology on centennial–millennial timescales, rather than a dominant influence from local SST variation.This work was financially supported by the US NSF and the Ocean Climate Change Institute of WHOI