Origin of TSL peaks located at 200–250 K in UV-irradiated PbWO4 crystals

Thermally stimulated luminescence (TSL) was studied for many ${\mathrm{PbWO}}_4$ crystals after their selective irradiation at 80–220 K in the 3.4–5.0 eV energy range to clarify the origin of the defects responsible for the TSL peaks located in the 200–250 K range. The conclusion is made that both in ${\mathrm{PbWO}}_4$ and ${\mathrm{PbWO}}_4$:$\mathrm{Mo}$ crystals the total TSL intensity and the intensity ratio of various TSL peaks are mainly determined by the concentration and type of oxygen and lead vacancies which depend on the crystal preparation and annealing conditions and on the concentration of trivalent rare-earth impurity ions. The TSL peak near 200 K is ascribed to $\{{\mathrm{Pb}}^{+}–{\mathrm{WO}}_3\}$ centers and the peak in the 210–230 K range, to the electron centers, containing oxygen vacancies of the type of ${\mathrm{WO}}_2$ and WO. Only the 250 K peak arises from electron ${\mathrm{MoO}}_4^{3-}$ centers. Thermally stimulated processes are accompanied with the green G(II) emission.     

Persistent luminescence and synchrotron radiation study of the Ca2MgSi2O7:Eu2+,R3+ materials

The tetragonal ${\mathrm{Ca}}_2{\mathrm{MgSi}}_2{\mathrm{O}}_7$:${\mathrm{Eu}}^{2+},{\mathrm{R}}^{3+}$ persistent luminescence materials were prepared by a solid state reaction. The UV excited and persistent luminescence was observed in the green region centred at 535 nm. Both luminescence phenomena are due to the same ${\mathrm{Eu}}^{2+}$ ion occupying the single ${\mathrm{Ca}}^{2+}$ site in the host lattice. The ${\mathrm{R}}^{3+}$ codoping usually reduced the persistent luminescence of ${\mathrm{Ca}}_2{\mathrm{MgSi}}_2{\mathrm{O}}_7$:${\mathrm{Eu}}^{2+}$, which differs from the ${\mathrm{M}}_2{\mathrm{MgSi}}_2{\mathrm{O}}_7$:${\mathrm{Eu}}^{2+}$ $(\mathrm{M}=\mathrm{Sr},\mathrm{Ba})$ and ${\mathrm{MAl}}_2{\mathrm{O}}_4$:${\mathrm{Eu}}^{2+}$ $(\mathrm{M}=\mathrm{Ca},\mathrm{Sr})$ materials. Only the ${\mathrm{Tb}}^{3+}$ ion enhanced slightly the persistent luminescence. With the aid of synchrotron radiation, the band gap energy of ${\mathrm{Ca}}_2{\mathrm{MgSi}}_2{\mathrm{O}}_7$:${\mathrm{Eu}}^{2+}$ was found to be about 7 eV that is very similar to those of the ${\mathrm{M}}_2{\mathrm{MgSi}}_2{\mathrm{O}}_7$:${\mathrm{Eu}}^{2+}$ $(\mathrm{M}=\mathrm{Sr},\mathrm{Ba})$ materials. Thermoluminescence results suggested that the ${\mathrm{R}}^{3+}$ ions might act as electron traps, but only the TL peaks created by ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ can be found in the temperature range accessible. Lattice defects (e.g. oxygen vacancies) are also important, since the same main thermoluminescence peak was observed at about $100{}^{\circ }\mathrm{C}$ with and without ${\mathrm{R}}^{3+}$ codoping.     

Electronic structure and optical properties of ABP2O7 double phosphates

Luminescence and luminescence excitation under VUV radiation of ${\mathrm{ABP}}_2{\mathrm{O}}_7$ ($\mathrm{A}=\mathrm{Na}$, K, Cs; $\mathrm{B}=\mathrm{Al}$, In) double phosphates are studied. Two emission bands peaking near 330 and 420 nm are common for investigated ${\mathrm{ABP}}_2{\mathrm{O}}_7$ crystals. The band structure and partial densities of electronic states of perfect ${\mathrm{KAlP}}_2{\mathrm{O}}_7$, ${\mathrm{LiInP}}_2{\mathrm{O}}_7$ and ${\mathrm{NaTiP}}_2{\mathrm{O}}_7$ crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. It is found that the structures of the conduction bands of ${\mathrm{ABP}}_2{\mathrm{O}}_7$ crystals, which have different B cations, are appreciably different. Experimental results are compared with results of calculations of the electronic structure. Assumptions concerning the origin of luminescence in double phosphates are made.     

Thermoluminescence properties of copper doped zirconium oxide for UVR dosimetry

The synthesized ${\mathrm{ZrO}}_2$:Cu particles were characterized using X-ray diffraction (XRD) to determine the nanocrystallite size and crystal structure, respectively. The ${\mathrm{ZrO}}_2$:Cu powder with a crystallite size of 30–40 nm has a monoclinic structure and exhibit a thermoluminescent (TL) glow curve with two peaks centered at 130 and $180{}^{\circ }\mathrm{C}$. The TL response of ${\mathrm{ZrO}}_2$:Cu as a function of wavelength exhibited two maxima at 260 and 290 nm. The TL response of ${\mathrm{ZrO}}_2$:Cu as a function of the UV light spectral irradiance was linear in the range from 10 to $2300\mathrm{mJ}/{\mathrm{cm}}^2$. Fading and reusability of the phosphor were also studied. The results showed that ${\mathrm{ZrO}}_2$:Cu nanopowder has potential to be used as a UV dosimeter in UV radiation monitoring.     

YbNi2: A heavy fermion ferromagnet

Measurements of the magnetization and specific heat of YbNi₂ binary alloy are reported. The DC magnetic susceptibility displays a ferromagnetic behavior with a Curie temperature T_C=10.5 K, one of the highest found in Yb compounds. Moreover, the temperature dependence of the specific heat exhibits a lambda anomaly with a peak of 5.12 J/mol K at 9.4 K. The analysis also shows an additional magnetic contribution around 32 K stemming from the crystalline electric field of a quartet at ${\Delta }_1=72\mathrm{K}$ and a doublet at ${\Delta }_2=126\mathrm{K}$, according to the splitting of the Yb³⁺ ion in cubic symmetry. From the magnetic contribution to the specific heat, a relatively high Kondo temperature $T_K=27\mathrm{K}$ is estimated. Below the magnetic transition, the specific heat shows a huge value of the electronic coefficient ${\gamma }_{\mathit{LT}}=573\mathrm{mJ}/\mathrm{mol}\mathrm{K}$, which is a signature of a heavy fermion behavior. Therefore, this alloy is a fine example of enhanced ferromagnetism and heavy fermion behavior among Yb compounds.     

Memory effect in MIS structures with amorphous silicon nanoparticles embedded in ultra thin SiOx matrix

Metal/${\mathrm{SiO}}_2$/a-Si-${\mathrm{SiO}}_x$/c-Si structures containing amorphous silicon nanoparticles (a-Si NPs) embedded in ultra thin ${\mathrm{SiO}}_x$ matrix are fabricated by thermal evaporation of ${\mathrm{SiO}}_x$ and sputtering of ${\mathrm{SiO}}_2$ layers followed by thermal annealing at $700{}^{\circ }\mathrm{C}$. A memory effect, due to charging of a-Si NPs in ${\mathrm{SiO}}_x$, is observed. The processes of NP charging and discharging are accomplished by applying pulses with alternative polarities. The observed shift of the flat band voltage of the high-frequency C–V curve caused by a voltage pulse of $-15\mathrm{V}$ having duration of 1 s is more than 3 V. In addition, the structures show good retention characteristics which make them promising for application in non-volatile memory devices.     

Triangle for the entropic index q of non-extensive statistical mechanics observed by Voyager 1 in the distant heliosphere

Tsallis [Physica A 340 (2004) 1) identified a set of numbers, the “q-triplet” ≡ {q_stat, q_sen, q_rel}, for a system described by non-extensive statistical mechanics. The deviation of the q's from unity is a measure of the departure from thermodynamic equilibrium. We present observations of the q-triplets derived from two sets of daily averages of the magnetic field strength B observed by Voyager 1 in the solar wind near 40 A.U. during 1989 and near 85 A.U. during 2002, respectively. The results for 1989 do not differ significantly from those for 2002. We find $q_{\mathrm{stat}}=1.75\pm 0.06$, $q_{\mathrm{sen}}=-0.6\pm 0.2$, and $q_{\mathrm{rel}}=3.8\pm 0.3$.     

Disorder dependence electron phonon scattering rate of V82Pd18 − xFex alloys at low temperature

We have systematically investigated the disorder dependence electron phonon scattering rate in three dimensional disordered V₈₂Pd_18 ? xFe_x alloys. A minimum in temperature dependence resistivity curve has been observed at low temperature $T=T_{\mathrm{m}}$. In the temperature range $5\text{ K}\le T\le T_{\mathrm{m}}$ the resistivity correction follows ${{\rho }_{\mathrm{o}}}^{5/2}{T}^{1/2}$ law. The dephasing scattering time has been calculated from analysis of magnetoresistivity by weak localization theory. The electron dephasing time is dominated by electron–phonon scattering and follows anomalous temperature (T) and disorder $({\rho }_0)$ dependence behaviour like ${\tau }_{\mathrm{e}\text{-}\mathrm{ph}}^{?1}\propto T^2/{\rho }_0$, where ${\rho }_0$ is the impurity resistivity. The magnitude of the saturated dephasing scattering time $({\tau }_0)$ at zero temperature decreases with increasing disorder of the samples. Such anomalous behaviour of dephasing scattering rate is still unresolved.     

Examining the fragmentation of 158 A GeV lead ions on copper target: Charge-changing cross sections

A stack of plastic CR-39 Track Detectors were exposed to 158 A GeV ²⁰⁷Pb ions at the CERN-SPS beam facility. The exposure of stack was performed at normal incidence with a fluence of about $1500\mathrm{ions}/{\mathrm{cm}}^2$. The total number of lead ions in each spill was about $7.8\times {10}^4$ with eight spills on each stack. For the stack with the Cu target, the lengths of etched cones on one face of the CR-39 detectors (before and after the target) were measured. Using these measurements and charge identification methodology in CR-39 track detectors, total and partial charge changing cross sections of 158 A GeV ${\mathrm{Pb}}^{82+}$ ions on Cu and CR-39 targets are determined in the charge region $63⩽Z⩽82$. The possibilities of presence and absence of odd–even effect in measured partial charge changing cross sections of 158 A GeV Pb ions for Cu and CR-39 targets are described. The charge resolution $({\sigma }_Z)$ achieved in the present experiment is $\sim 0.18\mathrm{e}$–0.21e. The analysis of discrepancies between our experimental results and other published results for the identical reaction is also presented.     

The recombination channels of luminescence excitation in YAG:Yb single crystalline films

Absorption and emission spectra, luminescence decay kinetics and thermostimulated luminescence of X-ray irradiated YAG:Yb single crystalline films were studied. Two emission bands peaked at 420 and 488 nm have been detected in the investigated films. The strong thermal quenching of luminescence band at 488 nm was observed above 160 K. The influence of growth conditions and annealing in air on the lifetime of ${\mathrm{Yb}}^{3+}$ ion excited state in the IR spectral region have been revealed. The recombination mechanisms of the $f–f$ transition at ${\mathrm{Yb}}^{3+}$ ion excitation, as well as the mechanism of lifetime shortening for the excited ${\mathrm{Yb}}^{3+}$ luminescence have been discussed.     

Orientation relationship between α-Fe precipitate and α-Al2O3 matrix in iron-implanted sapphire

Fe ions were implanted into α-Al₂O₃ single crystals (sapphire) at room temperature and annealed in a reducing atmosphere. The orientation relationships (ORs) between α-Fe particles and sapphire matrix were investigated using transmission electron microscopy (TEM). All the α-Fe particles have the orientation relationship (OR) of (1 1 1)_α-Fe || (0 0 0 1)_sapphire and ${[1\overline{1}0]}_{\alpha \text{-Fe}}\left|\right|{[11\overline{2}0]}_{\text{sapphire}}$ with sapphire. This OR is predicted precisely by the coincidence of reciprocal lattice points (CRLP) method. The other OR of (1 1 0)_α-Fe || (0 0 0 1)_sapphire and ${[111]}_{\alpha \text{-Fe}}\left|\right|{[5\overline{1}\overline{4}0]}_{\text{sapphire}}$ reported before is confirmed by the same method to be one of the secondary preferred orientation relationships in the α-Fe/sapphire system.     

Luminescent properties of Yb-doped LaSc3(BO3)4 under VUV excitation

Ytterbium doped borate crystals are promising laser media, e.g. in ${\mathrm{LaSc}}_3({\mathrm{BO}}_3{)}_4$ (LSB) matrices large distance between ytterbium ions results in reduced concentration quenching of the ytterbium f–f luminescence [Petermann, K., Fagundes-Peters, D., Johansen, O., Mond, M., Peters, V., Romero, J.J., Kutovoi, S., Speiser, J., Giesen, A., 2005. Highly Yb-doped oxides for thin-disc lasers. J. Crystal Growth 275, 135-140]. ${\mathrm{Yb}}^{3+}$ ions in complex oxides in addition to the 4f $\to$ 4f transitions often manifest fast charge transfer luminescence (CTL) in the UV-visible range. In some borates it was not observed at all, like in orthoborates of Sc, Y and La [Van Pieterson, L., Heeroma, M., de Heer, E., Meijerink, A., 2000. Charge transfer luminescence of ${\mathrm{Yb}}^{3+}$. J. Lumin. 91, 177–193]; in haloborates ${\mathrm{Sr}}_2{\mathrm{B}}_5{\mathrm{O}}_9\mathrm{X}$, where X = Cl, Br, the UV/visible luminescence was attributed to ytterbium CTL though it looked substantially different from other matrices [Dotsenko, V.P., Berezovskaya, I.V., Pyrogenko, P.V., Efryushina, N.P., Rodniy, P.A., Eijk van, C.W.E., Sidorenko, A.V., 2002. Valence states and luminescence properties of ytterbium ions in strontium haloborates. J. Solid State Chem. 166, 271–276]; while in oxyborate ${\mathrm{Li}}_2{\mathrm{Lu}}_5{\mathrm{O}}_4({\mathrm{BO}}_3{)}_3$ “classical” CTL was observed [Jubera, V., Garcia, A., Chaminade, J.P., Guillen, F., Sablayrolles, Jean, Fouassier, C., 2007. ${\mathrm{Yb}}^{3+}$ and ${\mathrm{Yb}}^{3+}\text{-}{\mathrm{Eu}}^{3+}$ luminescent properties of the ${\mathrm{Li}}_2{\mathrm{Lu}}_5{\mathrm{O}}_4({\mathrm{BO}}_3{)}_3$ phase. J. Lumin. 124(1), 10–14]. In this work the luminescence properties of another borate, namely LSB doped by Yb are presented.     

On the non-integrability of a generalized Darboux Halphen system

In this paper we study a generalized Darboux Halphen system given by ${\dot{x}}_1=x_2{x}_3-x_1(x_2+x_3)+{\tau }^2({\alpha }_1,{\alpha }_2,{\alpha }_3,x_1,x_2,x_3)\text{,}$${\dot{x}}_2=x_3{x}_1-x_2(x_3+x_1)+{\tau }^2({\alpha }_1,{\alpha }_2,{\alpha }_3,x_1,x_2,x_3)\text{,}$${\dot{x}}_3=x_1{x}_2-x_3(x_1+x_2)+{\tau }^2({\alpha }_1,{\alpha }_2,{\alpha }_3,x_1,x_2,x_3)\text{,}$ where $x_1$, $x_2$, $x_3$ are real variables, ${\alpha }_1,{\alpha }_2,{\alpha }_3$ are real constants and ${\tau }^2({\alpha }_1,{\alpha }_2,{\alpha }_3,x_1,x_2,x_3)={\alpha }_1^2(x_1-x_2)(x_3-x_1)+{\alpha }_2^2(x_2-x_3)(x_1-x_2)+{\alpha }_3^2(x_3-x_1)(x_2-x_3)\text{.}$ We prove that, for any $({\alpha }_1,{\alpha }_2,{\alpha }_3)\in {\mathbb{R}}^3\setminus \left\{(0,0,0)\right\}$, this system does not admit any non-constant global first integral that can be described by a formal power series. Furthermore, restricting the values of $({\alpha }_1,{\alpha }_2,{\alpha }_3)$ to a full Lebesgue measure set, we prove that this system does not admit any non-constant rational or Darbouxian global first integral. This is a first step toward proving that this system is chaotic.