Growth and optical property of Mg,Fe co-doped near-stoichiometric LiNbO3 crystal

The Mg-doped and undoped, Fe near-stoichiometric LiNbO₃ crystals were grown from the Li-rich melt by Czochralski technique. The UV-Vis absorption spectra and infrared transmittance spectra were measured to study the structure and defects of the crystals. The photo-damage resistance ability of the crystals was characterized by observing transmission facula distortion directly. The photo-damage resistance ability of Mg (3.0 mol%):Fe (0.01 wt.%):SLN is higher than that of Fe (0.01 wt.%):SLN and Fe (0.01 wt.%):CLN. This difference is attributed to the photoconductivity increase.     

Deterministic beam fanning in Fe-doped stoichiometric lithium niobate crystals

We investigated the beam-fanning effect in Fe-doped stoichiometric lithium niobate (Fe:SLN) crystals that were grown by the top-seeded solution growth method. Deterministic beam fanning (DBF) was measured in Z-cut Fe:SLN crystal for incident light propagating along the c+ and c- axes. The dependence of beam-fanning factors on incident power density was also studied. The experimental results of DBF in the Z-cut Fe:SLN crystal were in good agreement with a theoretical simulation based on a two-wave mixing model. The results compared with those for Fe-doped congruent lithium niobate crystals indicate that the beam-fanning process in Fe:SLN is deterministic because of its much-reduced intrinsic density of defects.     

Recombination activity of iron related complexes in silicon

Abstract

Recombination centres related to Fe complexes in p type Si are studied by carrier lifetime measurements using non-destructive microwave and light induced absorption techniques. The cross correlation of lifetime, density of electrically active Fe species, and structural defects is used to investigate the transformation and the precipitation of indiffused Fe. The recombination activity of Fe related defects isfound to depend on the injection level of excess carriers. Both thermal and photoactivation mechanisms are employed to decompose Fe–B pairs and to study the impact on the recombination time. The increase of high level injection lifetime due to photodissociation of Fe–B pairs is explained by a more efficient recombination via an acceptor level at E_e – 0.29 eV which has been derived from the temperature dependence of carrier lifetime. The mechanism of a recombination enhanced defect reaction is discussed on the basis of the experimental observations.     

Comparison of two-color hologram lifetimes of near-stoichiometric lithium niobate and of tantalate crystals

Lifetimes of two-color nonvolatile holograms recorded in undoped or in slightly doped near-stoichiometric lithium niobate and tantalate crystals were measured and compared by extrapolation of the high-temperature data. A proton-compensation mechanism dominated the dark decay and yielded similar activation energies, of 1.05 and 1.10 eV, for near-stoichiometric lithium niobate and tantalate crystals, respectively. The lifetime of holograms in lithium tantalate was 1 order of magnitude longer than that in lithium niobate with the same proton concentration, which was consistent with our theoretical estimation. The projected lifetime of two-color holograms in lithium tantalate without observable OH-absorption is longer than 50 years.     

Time resolved spectroscopic studies on some nanophosphors

Time resolved spectroscopy is an important tool for studying photophysical processes in phosphors. Present work investigates the steady state and time resolved photoluminescence (PL) spectroscopic characteristics of ZnS, ZnO and (Zn, Mg)O nanophosphors both in powder as well as thin film form. Photoluminescence (PL) of ZnS nanophosphors typically exhibit a purple/blue emission peak termed as self activated (SA) luminescence and emission at different wavelengths arising due to dopant impurities e.g. green emission for ZnS: Cu, orange emission for ZnS: Mn and red emission for ZnS: Eu. The lifetimes obtained from decay curves range from ns to ms level and suggest the radiative recombination path involving donor-acceptor pair recombination or internal electronic transitions of the impurity atom. A series of ZnMgO nanophosphor thin films with varied Zn: Mg ratios were prepared by chemical bath deposition. Photoluminescence (PL) excitation and emission spectra exhibit variations with changing Mg ratio. Luminescence lifetime as short as 10⁻¹⁰ s was observed for ZnO and ZnMgO (100: 10) nanophosphors. With increasing Mg ratio, PL decay shifts into microsecond range. ZnO and ZnMgO alloys up to 50% Mg were prepared as powder by solid state mixing and sintering at high temperature in reducing atmosphere. Time resolved decay of PL indicated lifetime in the microsecond time scale. The novelty of the work lies in clear experimental evidence of dopants (Cu, Mn, Eu and Mg) in the decay process and luminescence life times in II–VI semiconductor nanocrystals of ZnS and ZnO. For ZnS, blue self activated luminescence decays faster than Cu and Mn related emission. For undoped ZnO nanocrystals, PL decay is in the nanosecond range whereas with Mg doping the decay becomes much slower in the microsecond range.     

New Al2O3:C,Mg crystals for radiophotoluminescent dosimetry and optical imaging

Optical and dosimetric properties of a new radiophotoluminescent material based on aluminum oxide doped with carbon and magnesium (Al2O3:C,Mg) and having aggregate oxygen vacancy defects are presented. The Al2O3:C,Mg crystals are characterized by several new optical absorption and emission bands. It is suggested that the main optical properties of this material are due to the formation of aggregate defects composed of two oxygen vacancies and two Mg-impurity atoms. Radiation-induced optical absorption bands are centered at 335 and 620 nm and produce fluorescent emission at 750 nm with a 75 +/- 5 ns lifetime. The dose measurements are performed by illumination of the Al2O3:C,Mg crystal with 335 nm or 650 nm light and by measuring the intensity of the 750 nm fluorescence. The detector material is insensitive to room light before and after the irradiation and the traps are stable up to 600 degrees C. A dose measurement range between 5 mGy and 200 Gy, suitable for therapeutic radiology applications, was demonstrated. The short luminescent lifetime and nondestructive readout is favorable for imaging applications.     

Dechlorination of trichloroethylene in aqueous solution by noble metal-modified iron

Bimetallic particles are extremely interesting in accelerating the dechlorination of chlorinated organics. Four noble metals (Pd, Pt, Ru and Au), separately deposited onto the iron surface through a spontaneous redox process, promoted the TCE dechlorination rate, and the catalytic activity of the noble metal followed the order of Pd>Ru>Pt>Au. This order was found to be dependent on the concentrations of adsorbed atomic hydrogen, indicating that the initial reaction was cathodically controlled. Little difference in the distribution of the chlorinated products for the four catalysts (cis-DCE: 51%; 1,1-DCE: 27%; trans-DCE: 15% and VC: 7%) was observed. The chlorinated by-products accumulated in both Pt/Fe and Au/Fe (10.3% and 2.5% of the transformed TCE, respectively), but did not accumulate in Pd/Fe and Ru/Fe. Ru/Fe was further examined as an economical alternative to Pd/Fe. The 1.5% Ru/Fe was found to completely degrade TCE within 80 min. Considering the expense, the yield of chlorinated products and the lifetime of a reductive material, Ru provides a potential alternative to Pd as a catalyst in practical applications.     

Lifetime and leakage current considerations in metal-doped germanium

This paper discusses the impact of transition metal (TM) impurities in germanium on the electrical material and device characteristics, i.e., the recombination and generation lifetime and the leakage current in a p–n junction. As will be shown, most relevant data have been obtained in the fifties and sixties from Hall effect and lifetime measurements, while there is a lack of accurate Deep Level Transient Spectroscopy (DLTS) results on metal-doped Ge. It will be shown that the most efficient lifetime killers are Fe, Ni and most likely Co, while Cu, which is the most notorious contaminant, has little impact on the minority carrier lifetime. Owing to the asymmetry in the capture cross sections, n-type material will generally have a lower lifetime than p-Ge for the same concentration of substitutional metal centers. Due to the presence of near mid-gap acceptor levels, most TMs will be efficient leakage current generators at room temperature. However, the expected maximum values for the leakage current density are one to two decades smaller than what is typically found in state-of-the-art ion-implanted shallow p–n junctions in Ge. Paper to be published in the Proceedings of the 2nd CADRES Workshop, Crete, 8–11 September, 2006, J. Materials Sci: Materials in Electron.     

Development of LiF:Mg,Cu,Si TL material (new KLT-300) with a low-residual signal and high-thermal stability

LiF-based thermoluminescence (TL) materials have been widely used for radiation dosimetry due to their attractive features. LiF:Mg,Cu,P is one of the most sensitive tissue-equivalent TL materials, approximately 40 times more sensitive than LiF:Mg,Ti (TLD-100), but it has two main drawbacks: a thermal loss of the TL sensitivity when annealed at temperatures >240 degrees C, and a relatively high-residual signal. Recently, LiF:Mg,Cu,Na,Si TL material was developed to overcome these drawbacks at the Korea Atomic Energy Research Institute, but it provided only marginal improvements in reducing the residual signal. The newly developed LiF:Mg,Cu,Si TL material has a significantly lower residual signal and a better stability to thermal treatments. In this article, the preparation method and some dosimetric properties (sensitivity and residual signal) of the new LiF:Mg,Cu,Si TL material are presented. At the end of the preparation procedures, a dual-step annealing method is introduced and this has proved as a very efficient method to reduce the high-temperature peak and is the cause of residual signal. Therefore, the high-temperature peak in the glow curve was significantly reduced. The sensitivity is approximately 20 times higher than that of TLD-100 and the residual signal was estimated to be approximately 0.04%.     

Effect of iron and manganese contents on convection-free precipitation and sedimentation of primary α-Al(FeMn)Si phase in liquid Al-11.5Si-0.4Mg alloy

The effect of Fe and Mn contents on precipitation and sedimentation of primary -Al(FeMn)Si phase in liquid Al-11.5Si-0.4Mg (wt%) alloy has been investigated at 600°C in convection-free conditions. Almost all primary -Al(FeMn)Si particles and some oxide films seem to completely settle to the base of the melts. With the increase of original iron equivalent values (IEV) or Mn/Fe ratio at a given Fe level there are increases in particle weight, number and size. The particle volume fraction and depth of sediment also increase with IEV or Mn/Fe ratio at a given iron level. However, the particle volume fraction and average sizes probably remain plateaus with IEVs from 2 to 5.5. There is an equilibrium Mn content corresponding to a precipitation temperature for a given alloy. In Al-11.5Si-0.4Mg alloy containing 0.7–1.22Fe and 0.3–2.15Mn, Mn is approximately 0.3% after sedimentation at 600°C. The removal efficiency of Fe and Mn increases with original IEV or Mn/Fe ratio at a given Fe level. Mn has higher removal efficiency than Fe. Experimental results for primary particle amounts and compositions were compared to predictions from software JMatPro. Good agreement was found suggesting that the modelling route could be used to explore different alloys where sedimentation would take place.     

A comparative study on the domain switching characteristics of near stoichiometric lithium niobate and lithium tantalate single crystals

For pure SLN and SLT crystals the coercive field measured from ferroelectric hysteresis loop was found to be independent of ramp rate. Decreased lithium concentration in pure SLN samples, the coercive field and internal field are strongly enhanced. Nb_Li antisites are the major contribution to the internal field. Coercive field depends strongly on the ramp rate in case of MgSLN and MgSLT samples, because of domain pinning. The coercive field is considerably reduced in Mg doped SLN and SLT compared to pure samples, indicating that the switching fields are strongly dependent on the nonstoichiometry of the crystals. The coercive field values were found to be constant under multiple cycling in case of Mg (1 mol%) doped SLN crystal. A strong correlation is found to exist between coercive field value and the Curie temperature.     

CALPHAD simulation of the Mg–(Mn,Zr)–Fe system and experimental comparison with as-cast alloy microstructures as relevant to impurity driven corrosion of Mg-alloys

Four Mg alloys with variations in the ratio of Mn, Zr and Fe additions were cast and their microstructures analysed via electron microscopy. Thermodynamic calculations of the expected phases using PANDAT were evaluated with actual as-cast microstructures. Some of the as-cast alloys did appear to form phases similar to those anticipated from the PANDAT calculations. Furthermore, there was a new Mn–Fe particle interaction observed that was not predicted, but which is posited to be responsible for the increase in corrosion resistance among Mn containing Mg alloys with Fe impurities. The experimental work herein has been shown to be invaluable in the understanding of this practically important system with sparingly soluble Fe and its potential influence on the corrosion of Mg alloys.     

The redox state of the mantle during and just after core formation

Siderophile elements are depleted in the Earth's mantle, relative to chondritic meteorites, as a result of equilibration with core-forming Fe-rich metal. Measurements of metal-silicate partition coefficients show that mantle depletions of slightly siderophile elements (e.g. Cr, V) must have occurred at more reducing conditions than those inferred from the current mantle FeO content. This implies that the oxidation state (i.e. FeO content) of the mantle increased with time as accretion proceeded. The oxygen fugacity of the present-day upper mantle is several orders of magnitude higher than the level imposed by equilibrium with core-forming Fe metal. This results from an increase in the Fe2O3 content of the mantle that probably occurred in the first 1Ga of the Earth's history. Here we explore fractionation mechanisms that could have caused mantle FeO and Fe2O3 contents to increase while the oxidation state of accreting material remained constant (homogeneous accretion). Using measured metal-silicate partition coefficients for O and Si, we have modelled core-mantle equilibration in a magma ocean that became progressively deeper as accretion proceeded. The model indicates that the mantle would have become gradually oxidized as a result of Si entering the core. However, the increase in mantle FeO content and oxygen fugacity is limited by the fact that O also partitions into the core at high temperatures, which lowers the FeO content of the mantle. (Mg,Fe)(Al,Si)O3 perovskite, the dominant lower mantle mineral, has a strong affinity for Fe2O3 even in the presence of metallic Fe. As the upper mantle would have been poor in Fe2O3 during core formation, FeO would have disproportionated to produce Fe2O3 (in perovskite) and Fe metal. Loss of some disproportionated Fe metal to the core would have enriched the remaining mantle in Fe2O3 and, if the entire mantle was then homogenized, the oxygen fugacity of the upper mantle would have been raised to its present-day level.     

TL emission spectra from differently doped LiF:Mg detectors

There are two widely applied types of thermoluminescent detectors based on LiF:Mg luminophor: Lif:Mg,Ti and highly sensitive LiF:Mg,Cu,P. The role of luminescence centres in these materials is usually attributed to defects connected with, respectively, titanium and phosphorus dopants. In order to check how composition of dopants introduced into the LiF lattice influences emission spectra, measurements on a series of variously doped LiF:Mg samples were performed. Apart from LiF:Mg,Cu,P and LiF:Mg,Ti detectors with different concentration of activators, an experimental sample being a kind of a 'hybrid' between both standard materials was also prepared. It was synthesised with concentrations of magnesium and copper identical to those used for LiF:Mg,Cu,P preparation. but instead of phosphorus it was doped with titanium (LiF:Mg,Cu,Ti). The measurements of the emission spectra were performed by using a liquid nitrogen cooled CCD 1024E detector with an SP150 spectrograph. During the measurements the samples were placed inside a cryostat in a vacuum. Resulting data were numerically deconvoluted for individual peaks with respect to the wavelength and the temperature. The glow curve shape of this material resembles that of LiF:Mg,Cu,P, while sensitivity is at the level of LiF:Mg,Ti. Preliminary results indicate that emission of the LiF:Mg,Cu,Ti sample is similar to that of LiF:Mg,Cu,P rather than to LiF:Mg,Ti, showing a maximum for wavelengths well below 400 nm.     

A comparative study on the susceptibility of LiF:Mg,Ti (TLD-100) and LiF:Mg,Cu,P (TLD-100H) to spurious signals in thermoluminescence dosimetry

It is well known that spurious signals can occur in thermoluminescence dosimetry (TLD) whenever contaminants (i.e. dirt, oil, dust) are present on the surface of the TLD card or crystal during the read-out process. For TLD cards, the Teflon material can also contribute to the background noise and this contribution has been found to depend on the material's light absorption. These non-radiation-induced signals contribute to the total light output during TLD read-out and can lead to incorrect dosimetry especially for low-dose measurements such as personal dosimetry. However, these spurious signals are generally in the low-temperature channels and are mostly accompanied by abnormal glow curves. Most of the published reports dealing with this type of spurious TL signal are on the LiF:Mg,Ti (TLD-100) material. The relatively new TLD material, LiF:Mg,Cu,P, is more sensitive and has higher signal-to-noise ratio than the traditional LiF:Mg,Ti. In this study, the effects of disturbing signals to the LiF:Mg,Cu,P (TLD-100H) cards used in personal dosimetry are investigated and compared with those of LiF:Mg,Ti (TLD-100).     

Review of translocations detected by FISH for retrospective biological dosimetry applications

Several European laboratories have combined their research efforts to arrive at a consensus view on using fluorescence in situ hybridisation (FISH) for retrospective dosimetry. The aim of this review is to report these views and to highlight some areas where further work is needed. Translocations in the stable cells should be measured only in the cells that contain the full complement of the painted material. Two-way and one-way translocations should be combined with equal weight. The control level of translocations has a strong dependence on age, which has now been measured and the system has been calibrated. In conclusion, the technique works and a lifetime dose to the bone marrow from low-linear energy transfer radiation of 0.5 Gy above normal background levels can be measured for any individual. The main application is considered to provide an independent verification of lifetime doses to individuals who might form a part of an epidemiological study.     

Mg－Mn－Fe－O系热敏电阻变B值特性的研究

Ｍｇ－Ｍｎ－Ｆｅ－Ｏ系热敏电阻经还原处理后，具有低Ｂ高阻电学特性，不同于一般的ＮＴＣ热敏电阻，其Ｂ值随温度增加呈较大幅度的连续性增加。研究了还原条件、材料组分及烧结温度对样品电特性的影响，解释了Ｍｇ－Ｍｎ－Ｆｅ－Ｏ系热敏电阻的变Ｂ值机理     

Solid lipid nanoparticles incorporating melatonin as new model for sustained oral and transdermal delivery systems

melatonin (MT) is a hormone produced by the pineal gland at night, involved in the regulation of circadian rhythms. For clinical purposes, exogenous MT administration should mimic the typical nocturnal endogenous MT levels, but its pharmacokinetics is not favourable due to short half-life of elimination. Aim of this study is to examine pharmacokinetics of MT incorporated in solid lipid nanoparticles (SLN), administered by oral and transdermal route. SLN peculiarity consists in the possibility of acting as a reservoir, permitting a constant and prolonged release of the drugs included. In 7 healthy subjects SLN incorporating MT 3 mg (MT-SLN-O) were orally administered at 8.30 a.m. MT 3 mg in standard formulation (MT-S) was then administered to the same subjects after one week at 8.30 a.m. as controls. In 10 healthy subjects SLN incorporating MT were administered transdermally (MT-SLN-TD) by the application of a patch at 8.30 a.m. for 24 hours. Compared to MT-S, Tmax after MT-SLN-O administration resulted delayed of about 20 minutes, while mean AUC and mean half life of elimination was significantly higher (respectively 169944.7 +/- 64954.4 pg/ml x hour vs. 85148.4 +/- 50642.6 pg/ml x hour, p = 0.018 and 93.1 +/- 37.1 min vs. 48.2 +/- 8.9 min, p = 0.009). MT absorption and elimination after MT-SLN-TD demonstrated to be slow (mean half life of absorption: 5.3 +/- 1.3 hours; mean half life of elimination: 24.6 +/- 12.0 hours), so MT plasma levels above 50 pg/ml were maintained for at least 24 hours. This study demonstrates a significant absorption of MT incorporated in SLN, with detectable plasma level achieved for several hours in particular after transdermal administration. As dosages and concentrations of drugs included in SLN can be varied, different plasma level profile could be obtained, so disclosing new possibilities for sustained delivery systems.     

Two-color holography in reduced near-stoichiometric lithium niobate

We explored a number of factors affecting the properties relevant to holographic optical data storage by using a two-color recording scheme in reduced, near-stoichiometric lithium niobate. Two-color, or photon-gated, recording is achieved by use of 852-nm information-carrying beams and 488-nm gating light. Readout at 852 nm is nondestructive, with a gating ratio of ~10(4). Recording sensitivity, gating ratio, dynamic range, and dark decay were measured for crystals of differing stoichiometry, degree of reduction, wavelength of the gating light, temperature, and optical power density. The two-color sensitivity per incident photon is still somewhat less than that of the one-color process at 488 nm for ~1 W/cm(2) of gating light but is essentially the same in terms of absorbed photons. Two-color recording is an attractive way of achieving nondestructive readout in a read-write material, and it allows selective optical erasure.