Flexible Sensor for Wearable Vital Sign Monitoring System

In modern society, the body health is a very important issue to everyone. With the development of the science and technology, the new and developed body health monitoring device and technology will play the key role in the daily medical activities. This paper focus on making progress in the design of the wearable vital sign system. A vital sign monitoring system has been proposed and designed. The whole detection system is composed of signal collecting subsystem, signal processing subsystem, short-range wireless communication subsystem and user interface subsystem. The signal collecting subsystem is composed of light source and photo diode, after emiting light of two different wavelength, the photo diode collects the light signal reflected by human body tissue. The signal processing subsystem is based on the analog front end AFE4490 and peripheral circuits, the collected analog signal would be filtered and converted into digital signal in this stage. After a series of processing, the signal would be transmitted to the short-range wireless communication subsystem through SPI, this subsystem is mainly based on Bluetooth 4.0 protocol and ultra-low power System on Chip(SoC) nRF51822. Finally, the signal would be transmitted to the user end. After proposing and building the system, this paper focus on the research of the key component in the system, that is, the photo detector. Based on the study of the perovskite materials, a low temperature processed photo detector has been proposed, designed and researched. The device is made up of light absorbing layer, electron transporting and hole blocking layer, hole transporting and electron blocking layer, conductive substrate layer and metal electrode layer. The light absorbing layer is the important part of whole device, and it is fabricated by perovskite materials. After accepting the light, the electron-hole pair would be produced in this layer, and due to the energy level difference, the electron and hole produced would be transmitted to metal electrode and conductive substrate electrode through electron transporting layer and hole transporting layer respectively. In this way the response current would be produced. Based on this structure, the specific fabrication procedure including substrate cleaning; PEDOT:PSS layer preparation; pervoskite layer preparation; PCBM layer preparation; C60, BCP, and Ag electrode layer preparation. After the device fabrication, a series of morphological characterization and performance testing has been done. The testing procedure including film-forming quality inspection, response current and light wavelength analysis, linearity and response time and other optical and electrical properties testing. The testing result shows that the membrane has been fabricated uniformly; the device can produce obvious response current to the incident light with the wavelength from 350nm to 800nm, and the response current could be changed along with the light wavelength. When the light wavelength keeps constant, there exists a good linear relationship between the intensity of the response current and the power of the incident light, based on which the device could be used as the photo detector to collect the light information. During the changing period of the light signal, the response time of the device is several microseconds, which is acceptable working as a photo detector in our system. The testing results show that the device has good electronic and optical properties, and the fabrication procedure is also repeatable, the properties of the devices has good uniformity, which illustrates the fabrication method and procedure could be used to build the photo detector in our wearable system. Based on a series of testing results, the paper has drawn the conclusion that the photo detector fabricated could be integrated on the flexible substrate and is also suitable for the monitoring system proposed, thus made some progress on the research of the wearable monitoring system and device. Finally, some future prospect in system design aspect and device design and fabrication aspect are proposed.

Functional alkali tantalate 2D structures for microelectronics and related applications

Alkali tantalates and niobates, including K(Ta / Nb)O3, Li(Ta / Nb)O3 and Na(Ta / Nb)O3, are a very promising ferroic family of lead-free compounds with perovskite-like structures. Their versatile properties make them potentially interesting for current and future application in microelectronics, photocatalysis, energy and biomedics. Among them potassium tantalate, KTaO3 (KTO), has been raising interest as an alternative for the well-known strontium titanate, SrTiO3 (STO). KTO is a perovskite oxide with a quantum paraelectric behaviour when electrically stimulated and a highly polarizable lattice, giving opportunity to tailor its properties via external or internal stimuli. However problems related with the fabrication of either bulk or 2D nanostructures makes KTO not yet a viable alternative to STO. Within this context and to contribute scientifically to the leverage tantalate based compounds applications, the main goals of this thesis are: i) to produce and characterise thin films of alkali tantalates by chemical solution deposition on rigid Si based substrates, at reduced temperatures to be compatible with Si technology, ii) to fulfil scientific knowledge gaps in these relevant functional materials related to their energetics and ii) to exploit alternative applications for alkali tantalates, as photocatalysis. In what concerns the synthesis attention was given to the understanding of the phase formation in potassium tantalate synthesized via distinct routes, to control the crystallization of desired perovskite structure and to avoid low temperature pyrochlore or K-deficient phases. The phase formation process in alkali tantalates is far from being deeply analysed, as in the case of Pb-containing perovskites, therefore the work was initially focused on the process-phase relationship to identify the driving forces responsible to regulate the synthesis. Comparison of phase formation paths in conventional solid-state reaction and sol-gel method was conducted. The structural analyses revealed that intermediate pyrochlore K2Ta2O6 structure is not formed at any stage of the reaction using conventional solid-state reaction. On the other hand in the solution based processes, as alkoxide-based route, the crystallization of the perovskite occurs through the intermediate pyrochlore phase; at low temperatures pyrochlore is dominant and it is transformed to perovskite at >800 °C. The kinetic analysis carried out by using Johnson-MehlAvrami-Kolmogorow model and quantitative X-ray diffraction (XRD) demonstrated that in sol-gel derived powders the crystallization occurs in two stages: i) at early stage of the reaction dominated by primary nucleation, the mechanism is phase-boundary controlled, and ii) at the second stage the low value of Avrami exponent, n ~ 0.3, does not follow any reported category, thus not permitting an easy identification of the mechanism. Then, in collaboration with Prof. Alexandra Navrotsky group from the University of California at Davis (USA), thermodynamic studies were conducted, using high temperature oxide melt solution calorimetry. The enthalpies of formation of three structures: pyrochlore, perovskite and tetragonal tungsten bronze K6Ta10.8O30 (TTB) were calculated. The enthalpies of formation from corresponding oxides, ∆Hfox, for KTaO3, KTa2.2O6 and K6Ta10.8O30 are -203.63 ± 2.84 kJ/mol, - 358.02 ± 3.74 kJ/mol, and -1252.34 ± 10.10 kJ/mol, respectively, whereas from elements, ∆Hfel, for KTaO3, KTa2.2O6 and K6Ta10.8O30 are -1408.96 ± 3.73 kJ/mol, -2790.82 ± 6.06 kJ/mol, and -13393.04 ± 31.15 kJ/mol, respectively. The possible decomposition reactions of K-deficient KTa2.2O6 pyrochlore to KTaO3 perovskite and Ta2O5 (reaction 1) or to TTB K6Ta10.8O30 and Ta2O5 (reaction 2) were proposed, and the enthalpies were calculated to be 308.79 ± 4.41 kJ/mol and 895.79 ± 8.64 kJ/mol for reaction 1 and reaction 2, respectively. The reactions are strongly endothermic, indicating that these decompositions are energetically unfavourable, since it is unlikely that any entropy term could override such a large positive enthalpy. The energetic studies prove that pyrochlore is energetically more stable phase than perovskite at low temperature. Thus, the local order of the amorphous precipitates drives the crystallization into the most favourable structure that is the pyrochlore one with similar local organization; the distance between nearest neighbours in the amorphous or short-range ordered phase is very close to that in pyrochlore. Taking into account the stoichiometric deviation in KTO system, the selection of the most appropriate fabrication / deposition technique in thin films technology is a key issue, especially concerning complex ferroelectric oxides. Chemical solution deposition has been widely reported as a processing method to growth KTO thin films, but classical alkoxide route allows to crystallize perovskite phase at temperatures >800 °C, while the temperature endurance of platinized Si wafers is ~700 °C. Therefore, alternative diol-based routes, with distinct potassium carboxylate precursors, was developed aiming to stabilize the precursor solution, to avoid using toxic solvents and to decrease the crystallization temperature of the perovskite phase. Studies on powders revealed that in the case of KTOac (solution based on potassium acetate), a mixture of perovskite and pyrochlore phases is detected at temperature as low as 450 °C, and gradual transformation into monophasic perovskite structure occurs as temperature increases up to 750 °C, however the desired monophasic KTaO3 perovskite phase is not achieved. In the case of KTOacac (solution with potassium acetylacetonate), a broad peak is detected at temperatures <650 °C, characteristic of amorphous structures, while at higher temperatures diffraction lines from pyrochlore and perovskite phases are visible and a monophasic perovskite KTaO3 is formed at >700 °C. Infrared analysis indicated that the differences are due to a strong deformation of the carbonate-based structures upon heating. A series of thin films of alkali tantalates were spin-coated onto Si-based substrates using diol-based routes. Interestingly, monophasic perovskite KTaO3 films deposited using KTOacac solution were obtained at temperature as low as 650 °C; films were annealed in rapid thermal furnace in oxygen atmosphere for 5 min with heating rate 30 °C/sec. Other compositions of the tantalum based system as LiTaO3 (LTO) and NaTaO3 (NTO), were successfully derived as well, onto Si substrates at 650 °C as well. The ferroelectric character of LTO at room temperature was proved. Some of dielectric properties of KTO could not be measured in parallel capacitor configuration due to either substrate-film or filmelectrode interfaces. Thus, further studies have to be conducted to overcome this issue. Application-oriented studies have also been conducted; two case studies: i) photocatalytic activity of alkali tantalates and niobates for decomposition of pollutant, and ii) bioactivity of alkali tantalate ferroelectric films as functional coatings for bone regeneration. Much attention has been recently paid to develop new type of photocatalytic materials, and tantalum and niobium oxide based compositions have demonstrated to be active photocatalysts for water splitting due to high potential of the conduction bands. Thus, various powders of alkali tantalates and niobates families were tested as catalysts for methylene blue degradation. Results showed promising activities for some of the tested compounds, and KNbO3 is the most active among them, reaching over 50 % degradation of the dye after 7 h under UVA exposure. However further modifications of powders can improve the performance. In the context of bone regeneration, it is important to have platforms that with appropriate stimuli can support the attachment and direct the growth, proliferation and differentiation of the cells. In lieu of this here we exploited an alternative strategy for bone implants or repairs, based on charged mediating signals for bone regeneration. This strategy includes coating metallic 316L-type stainless steel (316L-SST) substrates with charged, functionalized via electrical charging or UV-light irradiation, ferroelectric LiTaO3 layers. It was demonstrated that the formation of surface calcium phosphates and protein adsorption is considerably enhanced for 316L-SST functionalized ferroelectric coatings. Our approach can be viewed as a set of guidelines for the development of platforms electrically functionalized that can stimulate tissue regeneration promoting direct integration of the implant in the host tissue by bone ingrowth and, hence contributing ultimately to reduce implant failure.

Investigating the cosmic-ray ionization rate in the galactic interstellar medium through observations of H3+

Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray ionization rate (zeta_2) is about 1 order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H3+ observations to 50, with detections in 21 of those. Ionization rates inferred from these detections are in the range (1.7+-1.0)x10^-16 s^-1 < zeta_2 < (10.6+-6.8)x10^-16 s^-1 with a mean value of zeta_2=(3.3+-0.4)x10^-16 s^-1. Upper limits (3sigma) derived from non-detections of H3+ are as low as zeta_2 < 0.4x10^-16 s^-1. These low upper-limits, in combination with the wide range of inferred cosmic-ray ionization rates, indicate variations in zeta_2 between different diffuse cloud sight lines. Calculations of the cosmic-ray ionization rate from theoretical cosmic-ray spectra require a large flux of low-energy (MeV) particles to reproduce values inferred from observations. Given the relatively short range of low-energy cosmic rays --- those most efficient at ionization --- the proximity of a cloud to a site of particle acceleration may set its ionization rate. Variations in zeta_2 are thus likely due to variations in the cosmic-ray spectrum at low energies resulting from the effects of particle propagation. To test this theory, H3+ was observed in sight lines passing through diffuse molecular clouds known to be interacting with the supernova remnant IC 443, a probable site of particle acceleration. Where H3+ is detected, ionization rates of zeta_2=(20+-10)x10^-16 s^-1 are inferred, higher than for any other diffuse cloud. These results support both the concept that supernova remnants act as particle accelerators, and the hypothesis that propagation effects are responsible for causing spatial variations in the cosmic-ray spectrum and ionization rate. Future observations of H3+ near other supernova remnants and in sight lines where complementary ionization tracers (OH+, H2O+, H3O+) have been observed will further our understanding of the subject.

Hydrothermal-vent alvinellid polychaete dispersal in the eastern Pacific .1. Influence of vent site distribution, bottom currents, and biological patterns

Deep-sea hydrothermal-vent habitats are typically linear, discontinuous, and short-lived. Some of the vent fauna such as the endemic polychaete family Alvinellidae are thought to lack a planktotrophic larval stage and therefore not to broadcast-release their offspring. The genetic evidence points to exchanges on a scale that seems to contradict this type of reproductive pattern. However, the rift valley may topographically rectify the bottom currents, thereby facilitating the dispersal of propagules between active vent sites separated in some cases by 10s of kilometers or more along the ridge axis. A propagule flux model based on a matrix of intersite distances, long-term current-meter data, and information on the biology and ecology of Alvinellidae was developed to test this hypothesis. Calculations of the number of migrants exchanged between two populations per generation (N-m) allowed comparisons with estimates obtained from genetic studies. N, displays a logarithmic decrease with increasing dispersal duration and reaches the critical value of 1 after 8 d when the propagule Aux model was run in standard conditions. At most, propagule traveling time cannot reasonably exceed 15-30 d, according to the model, whereas reported distances between sites would require longer lasting dispersal abilities. Two nonexclusive explanations are proposed. First, some aspects of the biology of Alvinellidae have been overlooked and long-distance dispersal does occur. Second, such dispersal never occurs in Alvinellidae, but the spatial-temporal dynamics of vent sites over geological timescales allows short-range dispersal processes to maintain gene flow.

Comando e Controlo na Artilharia Antiaérea

O presente trabalho, subordinado à temática “Comando e Controlo na Artilharia Antiaérea”, pretende problematizar algumas das questões mais recentes relativas a matérias de segurança e defesa, fruto dos mais recentes acontecimentos. Por exemplo, refira-se o abate do voo comercial na Ucrânia, entre outros inúmeros casos que se constituem como fatores que levam a questionar a capacidade de defesa dos Estados face ao fácil acesso e baixo custo destes meios, à mercê de pessoas/organizações criminosas e terroristas. Assim, é premente a necessidade de aquisição, por parte dos Estados, nomeadamente de Portugal, de uma Artilharia mais robusta e com um sistema de Comando e Controlo automático capaz de combater as potenciais e prováveis ameaças aéreas. Esta investigação pretende, então, analisar o atual sistema de Comando e Controlo da Artilharia Antiaérea nacional, por forma a identificar as suas capacidades e, em paralelo, as suas vulnerabilidades. Concomitantemente pretende-se analisar o sistema perante as ameaças aéreas e as operações que deverá executar no âmbito dos compromissos internacionais, com o objetivo fulcral de identificar prováveis potencialidades que deverão integrar o referido sistema. Pretende-se, deste modo, propor uma revisão do atual sistema no sentido de colmatar as suas prováveis lacunas e capacitando-o para uma resposta eficaz e efetiva perante eventuais ameaças, na esteira dos compromissos internacionais. No início apresentamos uma ‘revisão de literatura’ para que o leitor se familiarize com os conceitos e nomenclatura em uso nesta reflexão. Subsequentemente, expõe-se a metodologia empregue e são abordados os sistemas de Defesa Aérea e de Artilharia Antiaérea e, posteriormente, o Comando e Controlo. De seguida, apresenta-se uma análise possível dos dados provenientes das entrevistas executadas. Baseando-nos na investigação realizada, conclui-se que a Artilharia Antiaérea corre o risco sério de não dispor de capacidade de defesa, a baixa e muito baixa altitude, se não forem adquiridos rapidamente os materiais imprescindíveis para que os sistemas possam cabalmente atuar.

Test de step y capacidad de trabajo en jugadoras de voleibol: la paradoja de un mejor rendimiento en las jugadoras mayores

El objetivo del presente estudio fue comparar dos pruebas submáximas de capacidad aeróbica, el YMCA step test y la prueba de capacidad de trabajo físico a 170 ppm (P170) de frecuencia cardíaca (FC), en jugadoras de voleibol femenino. Se analizaron en 152 participantes variables antropométricas, el rendimiento, la frecuencia cardiaca final (Stepend) y la frecuencia cardiaca en el primer minuto de recuperación (Steprec) en la prueba YMCA step test, la P170 fue analizada expresando los resultados en valores absolutos (P170,abs, W) y relativos (P170,rel, W.kg-1). Además, un subgrupo (n=14) fue analizado otra vez después de un año. Los resultados mostraron como el YMCA step test correlacionó altamente (Steprec) y muy altamente (Stepend) con la P170 rel (r = –0.58 and r = –0.76, p < 0.001, respectively), y con la P170,abs (r = –0.54 and r = –0.68, p < 0.001, respectively). No se encontraron correlaciones entre los porcentajes de cambio en los test de capacidad aeróbica después de un año (p>0.05). La edad presentó una correlación baja a moderada con todos los índices de capacidad aeróbica (0.23 ≤ ŇrŇ ≤ 0.45, p<0.05), viendo como las mayores edades tenían una mejor capacidad aeróbica. Basándonos en estos resultados podemos concluir que la prueba YMCA step test (especialmente el parámetro Stepend) y la P170 podrian ser utilizadas indistintamente por entrenadores y preparadores físicos para monitorizar la capacidad aeróbica de jugadoras de voleibol. El paradójico incremento de la capacidad aeróbica con la edad puede ser atribuido a los métodos de evaluación utilizados que están basados en la FC y al descenso de la FC máxima con la edad. Por lo tanto, estos test deberían ser utilizados solo con edades inferiores.

Changes in movements of white seabream (Diplodus sargus) during the reproductive season

It has been hypothesized, based on anecdotal information and reports, that adult white seabream migrate and aggregate during spawning. Because most of the past telemetric studies on this ecologically and commercially important species were short in duration and did not cover the reproductive season, we set out to use longer-term passive acoustic telemetry to test this hypothesis. We found that white seabream expands its home range and increases the frequency of forays during the reproductive season, but found no obvious signs of spawning aggregations. Our results thus provide evidence for short-range behavioral shifts in fish space use related to reproductive activity, and support the notion that small MPAs may be effective in managing reef fish populations by effectively protecting their spawning biomass. (c) 2015 Elsevier Ltd. All rights reserved.

Quarkonia and heavy-light mesons in a covariant quark model

Preliminary calculations using the Covariant Spectator Theory (CST) employed a scalar linear confining interaction and an additional constant vector potential to compute the mesonic mass spectra. In this work we generalize the confining interaction to include more general structures, in particular a vector and also a pseudoscalar part, as suggested by a recent study. A one-gluon-exchange kernel is also implemented to describe the short-range part of the interaction. We solve the simplest CST approxima- tion to the complete Bethe-Salpeter equation, the one-channel spectator equation, using a numerical technique that eliminates all singularities from the kernel. The parameters of the model are determined through a fit to the experimental pseudoscalar meson spectra, with a good agreement for both quarkonia and heavy-light states.

Lithic economy and territory of Epipaleolithic hunter–gatherers in the Middle Tagus: The case of Pena d'Água (Portugal)

In Central Portugal (westernmost Eurasia) the transition from the traditional Pleistocene hunter–gatherer societies to the complex Mesolithic societies of the Holocene has been debated for decades. While some argue that these differences were a progressive phenomenon that started with the shift from the Pleistocene to the Holocene, others defend that the Late Pleistocene patterns were fairly similar to those of the Epipaleolithic and that the major shift was rapid, dramatic and triggered by the necessary adaptation to the 8.2 ka cal BP (8.09–8.25 ka cal BP) climatic event. The study of lithic raw material provenance might be useful for this discussion, since it has been suggested that the Magdalenian and Epipaleolithic populations from this region were collecting this resources within a close range territory, whereas the Mesolithic populations were acquiring them at longer distances. In this paper, we present the results from p-XRF, VP-SEM-EDS and μ-XRD analysis done on the Epipaleolithic lithic assemblage from Pena d'Água Rockshelter, and in some geological samples from secondary sources located ∼14 km from this site. This layer is of major relevance for this debate since it is dated from 8.19 ka cal BP. If the transition was gradual, it would be expected that this assemblage would show some traits of higher-complexity seen in the Mesolithic, namely of longer distance acquisition. However, our results indicate correspondence between the archaeological chert types and some of the geological sources. The differences seen between the archaeological specimens and geological samples are mostly present in traits that can be related with manufacture, handling and post-depositional phenomena. The results suggest that, in what concerns to the economy of abiotic resources, the Epipaleolithic populations living at the time of the dramatic 8.2 ka cal BP cold event, were performing a short range acquisition of lithic raw materials which reinforces the idea of continuity from the Late Pleistocene to the 8.2 ka cal BP event and an abrupt and dramatic shift soon after this phenomena.

Efficient wireless coverage of in-building environments with low electromagnetic impact

The city of tomorrow is a major integrating stake, which crosses a set of major broad spectrum domains. One of these areas is the instrumentation of this city and the ubiquity of the exchange of data, which will give the pulse of this city (sensors) and its breathing in a hyper-connected world within indoor and outdoor dense areas (data exchange, 5G and 6G). Within this context, the proposed doctorate project has the objective to realize cost- and energy- effective, short-range communication systems for the capillary wireless coverage of in-door environments with low electromagnetic impact and for highly dense outdoor networks. The result will be reached through the combined use of: 1) Radio over Fiber (RoF) Technology, to bring the Radio Frequency (RF) signal to the different areas to be covered. 2) Beamforming antennas to send in real time the RF power just in the direction(s) where it is really necessary.

Multiscale modeling of light-harvesting systems based on rhodamine B aggregates

Rhodamine B (RB) has been successfully exploited in the synthesis of light harvesting systems, but since RB is prone to form dimers acting as quenchers for the fluorescence, high energy transfer efficiencies can be reached only when using bulky and hydrophobic counterions acting as spacers between RBs. In this PhD thesis, a multiscale theoretical study aimed at providing insights into the structural, photophysical and optical properties of RB and its aggregates is presented. At the macroscopic level (no atomistic details) a phenomenological model describing the fluorescence decay of RB networks in presence of both quenching from dimers and exciton-exciton annihiliation is presented and analysed, showing that the quenching from dimers affects the decay only at long times, a feature that can be exploited in global fitting analysis to determine relevant chemical and photophysical information. At the mesoscopic level (atomistic details but no electronic structure) the RB aggregation in water in presence of different counterions is studied with molecular dynamics (MD) simulations. A new force field has been parametrized for describing the RB flexibility and the RB-RB interaction driving the dimerization. Simulations correctly predict the RB/counterion aggregation only in presence of bulky and hydrophobic counterion and its ability to prevent the dimerization. Finally, at the microscopic level, DFT calculations are performed to demonstrate the spacing action of bulky counterions, but standard TDDFT calculations are showed to fail in correctly describing the excited states of RB and its dimers. Moreover, also standard procedures proposed in literature for obtaining ad hoc functionals are showed to not work properly. A detailed analysis on the effect of the exact exchange shows that its short-range contribution is the crucial quantity for ameliorating results, and a new functional containing a proper amount of such an exchange is proposed and successfully tested.

Short- and medium-term effects of manual therapy on cervical active range of motion and pressure pain sensitivity in latent myofascial pain of the upper trapezius muscle: a randomized controlled trial

Objective: The purpose of this study was to investigate effects of different manual techniques on cervical ranges of 17 motion and pressure pain sensitivity in subjects with latent trigger point of the upper trapezius muscle. 18 Methods: One hundred seventeen volunteers, with a unilateral latent trigger point on upper trapezius due to computer 19 work, were randomly divided into 5 groups: ischemic compression (IC) group (n = 24); passive stretching group (n = 20 23); muscle energy technique group (n = 23); and 2 control groups, wait-and-see group (n = 25) and placebo group 21 (n = 22). Cervical spine range of movement was measured using a cervical range of motion instrument as well as 22 pressure pain sensitivity by means of an algometer and a visual analog scale. Outcomes were assessed pretreatment, 23 immediately, and 24 hours after the intervention and 1 week later by a blind researcher. A 4 × 5 mixed repeated- 24 measures analysis of variance was used to examine the effects of the intervention and Cohen d coefficient was used. 25 Results: A group-by-time interaction was detected in all variables (P b .01), except contralateral rotation. The 26 immediate effect sizes of the contralateral flexion, ipsilateral rotation, and pressure pain threshold were large for 3 27 experimental groups. Nevertheless, after 24 hours and 1 week, only IC group maintained the effect size. 28 Conclusions: Manual techniques on upper trapezius with latent trigger point seemed to improve the cervical range of 29 motion and the pressure pain sensitivity. These effects persist after 1 week in the IC group. (J Manipulative Physiol 301 Ther 2013;xx:1-10)

Photo luminescence: A probe for short, medium and long-range self-organization order in ZrTiO4 oxide

Photoluminescent disordered ZrTiO4 powders were obtained by the polymeric precursor soft-chemical method. This oxide system (ordered and disordered) was characterized by photoluminescence, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry and UV vis absorption experiments. The UV absorption tail formation in the disordered oxides was related to the diminution of optical band gap. In the disordered phase, this oxide displayed broad band photoluminescence caused by change in coordination number of titanium and zirconium with oxygen atoms. The gap decreased from 3.09 eV in crystalline oxide to 2.16 eV in disordered oxide. The crystalline oxide presented an orthorhombic alpha-PbO2-type structure in which Zr4+ and Ti4+ were randomly distributed in octahedral coordination polyhedra with oxygen atoms. The amorphous-crystalline transition occurred at almost 700 degrees C, at which point the photoluminescence vanished. The Raman peak at close to 80-200 cm(-1) indicated the presence of locally ordered Ti-O-n and Zr-O-n polyhedra in disordered photoluminescent oxides. (c) 2006 Elsevier B.V. All rights reserved.

Quantification of Short and Medium Range Order in Mixed Network Former Glasses of the System GeO2-NaPO3: A Combined NMR and X-ray Photoelectron Spectroscopy Study

Glasses in the system xGeO(2)-(1-x)NaPO3 (0 <= x <= 0.50) were prepared by conventional melting quenching and characterized by thermal analysis, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and P-31 nuclear magnetic resonance (MAS NMR) techniques. The deconvolution of the latter spectra was aided by homonuclear J-resolved and refocused INADEQUATE techniques. The combined analyses of P-31 MAS NMR and O-1s XPS lineshapes, taking charge and mass balance considerations into account, yield the detailed quantitative speciations of the phosphorus, germanium, and oxygen atoms and their respective connectivities. An internally consistent description is possible without invoking the formation of higher-coordinated germanium species in these glasses, in agreement with experimental evidence in the literature. The structure can be regarded, to a first approximation, as a network consisting of P-(2) and P-(3) tetrahedra linked via four-coordinate germanium. As implied by the appearance of P-(3) units, there is a moderate extent of network modifier sharing between phosphate and germanate network formers, as expressed by the formal melt reaction P-(2) + Ge-(4) -> P-(3) + Ge-(3). The equilibrium constant of this reaction is estimated as K = 0.52 +/- 0.11, indicating a preferential attraction of network modifier by the phosphorus component. These conclusions are qualitatively supported by Raman spectroscopy as well as P-31{Na-23} and P-31{Na-23} rotational echo double resonance (REDOR) NMR results. The combined interpretation of O-1s XPS and P-31 MAS NMR spectra shows further that there are clear deviations from a random connectivity scenario: heteroatomic P-O-Ge linkages are favored over homoatomic P-O-P and Ge-O-Ge linkages.