The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

How useful is SBF in predicting in vivo bone bioactivity

Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

The Mechanics of Earthquakes and Faulting

Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering

The Judd-Ofelt intensity parameters, ${\mathrm{\ensuremath{\Omega}}}_{\mathit{t}}$ (t=2,4,6) for f-f transitions of ${\mathrm{Er}}^{3+}$ ions doped in ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$-${\mathit{R}}_{2}$O (R=Na,K) glasses were determined from optical-absorption measurements, and their compositional dependence was investigated systematically. The values of ${\mathrm{\ensuremath{\Omega}}}_{2}$ exhibited a maximum around 25 mol % ${\mathit{R}}_{2}$O, while those of ${\mathrm{\ensuremath{\Omega}}}_{4}$ and ${\mathrm{\ensuremath{\Omega}}}_{6}$ decreased monotonically with an increase in ${\mathit{R}}_{2}$O content. The compositional dependences of ${\mathrm{\ensuremath{\Omega}}}_{4,6}$ were consistent with those of the isomer shift in $^{151}\mathrm{Eu}$ M\"ossbauer spectroscopy, which gives information about the 6s-electron density of ${\mathrm{Eu}}^{3+}$ ions. The variation of ${\mathrm{\ensuremath{\Omega}}}_{2}$ against ${\mathit{R}}_{2}$O content was related to the change in asymmetry of the rare-earth ligand due to the structural mixing of borate groups, while those of ${\mathrm{\ensuremath{\Omega}}}_{4,6}$ were related to the local basicity of rare-earth sites in the glass.

Compositional dependence of Judd-Ofelt parameters of Er3+ ions in alkali-metal borate glasses.

It has been confirmed that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body. It has been proposed that a hydrated silica formed on the surfaces of these materials in the body plays an important role in forming the surface apatite layer, but this has not yet been proved. In the present study, it is shown experimentally that a pure hydrated silica gel can induce apatite formation on its surface in a simulated body fluid when its starting pH is increased from 7.2 to 7.4.

Apatite Formation Induced by Silica Gel in a Simulated Body Fluid

The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces in the body. Our previous study showed that a silica gel prepared by hydrolysis and polycon- densation of tetraethoxysilane in aqueous solution containing poly(ethy1ene glycol) induces apatite nucleation on its surface in a simulated body fluid. In the present study, the effects of heat treatment of silica gel on its catalytic effects in apatite nucleation was investigated in a simulated body fluid. I t was found that apatite forms on the surfaces of silica gels heat-treated below 8OO°C, but not on those heat-treated above 900°C. The volume of nanometer-range pores in the gel remarkably decreased by heat treatment above 900°C. The concentration of silanol groups in the silica gels gradually decreased with increasing heat treatment temperature. The rate of silica dissolution from the gel into the simulated body fluid decreased remarkably by heat treatment above 900°C. This suggested that a special type of silanol group which is formed by soaking the gel treated below 800°C into the simulated body fluid is respon sible for apatite nucleation.

Dependence of apatite formation on silica gel on its structure : effect of heat treatment

Effect of skeleton size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography

Phase separations of gelling solutions have been investigated for acid-catalyzed, alkoxysilane-based systems containing polyacrylic acid (HPAA). Gels with micrometer-range interconnected porous morphologies were obtained in a composition range broader than that reported for the systems containing sodium polystyrene sulfonate. It is suggested that the data of a light-scattering experiment can be explained by the occurrence of spinodal phase separation which forms an interconnected morphology. The analogy between a chemical crosslinking reaction and a finite-rate cooling of a network-forming liquid is introduced, on which basis the effects of compositional parameters on the resultant gel morphology are explained.

Naohiro Soga

Papers

Compositional dependence of Judd-Ofelt parameters of Er3+ ions in alkali-metal borate glasses.

Apatite Formation Induced by Silica Gel in a Simulated Body Fluid

Dependence of apatite formation on silica gel on its structure : effect of heat treatment

Effect of skeleton size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography

Phase separation in silica sol-gel system containing polyacrylic acid I. Gel formaation behavior and effect of solvent composition