ac anddc electroluminescence in CaS:Cu,Sm phosphors

Theac anddc electroluminescence in CaS:Cu, Sm have been investigated. The luminescence spectra show three peaks in the visible region. The brightness-voltage dependence satisfies the relationB=B ₀ exp (−b/V ^1/2) with two modes of variation. The nature of this dependence indc andac at different frequencies is discussed. The electroluminescence brightness also depends on the temperature of the phosphors and shows a peak around 80.0;C. The electroluminescence efficiency increases with applied voltage up to 2200 V and this dependence on V is explained on the basis of a transport process of the Schottky emission type.     

Photo and electroluminescence of ZnO : Er and ZnO : Ag,Er electroluminors

A number of ZnO : Er and ZnO : Ag, Er electroluminors have been prepared and their photo (PL) and electroluminescent (EL) properties investigated. While the addition of Ag slightly shifts the PL spectra towards longer wavelength side, the EL spectra not only shift but consist of some new transitions. In ZnO : Er electroluminors, additional transitions also exist at higher frequencies of excitations. Brightness waves for this system consist of two secondary peaks during each half cycle of exciting field. Temperature dependence shows two broad peaks. While voltage dependence of ZnO : Er satisfies the relationB=B ₀ exp(−b/V ^1/2), the relationB=B ₀ V exp(−b/V ^1/2) is found to be suitable for ZnO : Ag, Er electroluminor. Possible mechanisms for these phenomena have been proposed. A preliminary account of this work was presented at the International Symposium on Solid State Physics held at the Indian Association for the Cultivation of Science, Calcutta in January 1977.     

Optical absorption spectrum of Cr3+ in natural ruby

Two sharp line-like bands calledN andR lines on the red side, a close doublet (B lines) on the violet side and two broad bands are observed for natural ruby. At liquid air temperature the splitting ofR line was found and also three sharp-bands calledR, R′ andB lines are identified with spin-forbidden transitions of² E,² T ₁ and² T ₂. The two broad bands calledU band andY band are assigned accordingly to the spin-allowed transitions⁴ T ₂ and⁴ T ₁ respectively. The observed bands of natural ruby have been attributed to Cr³⁺ ion in an octahedral environment with trigonal distortion. The crystal field parameters which gave a good fit to the observed band positions areB=732 cm⁻¹,C=4.25B,Dq=1830 cm⁻¹,V=−1996 cm⁻¹ andλ=34 cm⁻¹.     

Structural phase transitions in Pd0.8 Si0.2 and Pd0.75 Si0.20 Ag0.05 alloys observed by pac

The phase transition in the alloys Pd_0.8 Si_0.2 and Pd_0.75 Si_0.20 Ag_0.05 have been investigated through the quadrupole interaction of¹¹¹Cd impurities. The quadrupole interactions were measured by means of the TDPAC technique from room temperature up to about 870 K. The variation of the quadrupole interaction with temperature in the alloy PdSiAg shows aT ^3/2 dependence below and above 629 K, with coefficientsB=5.43(25)·10⁻⁵ K^−3/2 andB=3.70(15)·10⁻⁵ K^−3/2, respectively. This demonstrates that the alloy undergoes a phase transition around 629 K. The existence of two electric field gradients observed in the alloy PdSi,V _zz (1)=3.47(54)·10¹⁷ V/cm² andV _zz (2)=2.29(36)·10¹⁷ V/cm², indicates that there are two different¹¹¹Cd sites. The corresponding fractionsf ₁ andf ₂ strongly depend on temperature. Below 520 K, most¹¹¹Cd nuclei are subject to the higher EFGV _zz (1) (f ₁≈70%), whereas above 520 Kf ₁ falls rapidly to zero andV _zz (2) becomes dominant. The temperature dependences of thef ₁ andf ₂ reveal a picture of the phase transition between the two crystal structures.     

Hadronic weak decays of heavy mesons and nonfactorization

The parametersχ _1,2, which measure nonfactorizable soft gluon contributions to hadronic weak decays of mesons, are updated by extracting them from the data ofD, B→PP, VP decays (P: pseudoscalar meson,V: vector meson). It is found thatχ ₂ ranges from −0.36 to −0.60 in the decays fromD→Kπ toD ⁺→φπ ⁺,D→K*π, while it is of order 10% with a positive sign inB→ψK, Dπ, D*π, Dρ decays. Therefore, the effective parametera ₂ is process dependent in charm decay, whereas it stays fairly stable inB decay. This is in accordance with the picture that nonfactorizable soft gluon effects become stronger when the relative momentum of the decay particles becomes smaller. As forD, B→VV decays, the presence of nonfactorizable terms in general prevents a possible definition of effectivea ₁ anda ₂. This is reinforced by the observation of a large longitudinal polarization fraction inB→ψK* decay, implying nonfactorizable effects contributing differently toS-, P- andD-wave amplitudes. We found thatA ₁ ^nf /A ₁>0>A ₂ ^nf /A ₂,V ^nf/V (nf standing for nonfactorization) forB→ψK* decay and 0>A ₁ ^nf /A ₁>A ₂ ^nf /A ₂,V ^nf/V forD→K*ρ decay. A measurement of longitudinally and transversely polarized decay rates Γ _L and Γ _T in color-suppressed decay modesB ⁰→D*⁰ ρ ⁰,D*⁰ ω andD ⁺→φρ ⁺ is urged.     

A. C. Electroluminescence of CdS : Sm and CdS : Cu,Sm EL phosphors

Electroluminescent CdS : Sm and CdS : Cu, Sm phosphors have been prepared and their EL characteristics are investigated. The brightness waves of these phosphors were measured at a sinusoidal alternating voltages with a frequency of 500 Hz, 1 kHz, 2 kHz and 5 kHz. One primary and one secondary peak have been observed in each half period of the applied sinusoidal field. Time averaged EL brightness has been found to follow the Alfrey-Taylor relationB= =B ₀ exp (–b/V ^1/2) over a wide range of frequencies. Variation of the constants of this relation with frequency of the applied field have been studied. Variation of current across the EL cell with the applied voltage has also been investigated. The EL emission spectra show peaks at 600 and 650 nm in CdS : Sm phosphor whereas in the case of CdS : Cu, Sm phosphor the emission peak occurs at 600 nm. The observed results have been interpreted in terms of acceleration collision theory of the electroluminescence.One of the authors (RKT) expresses his gratitude to the University Grants Commission, New Delhi, for a fellowship and the Principal, S. D. J. Post Graduate College, Chandesar Azamgarh, for study leave.     

Laser photoacoustic spectroscopy of iodine molecule: Single and two-photon absorption

Photoacoustic spectroscopy of iodine molecule has been studied in gas phase using nitrogen laser-pumped tunable dye laser. The experiment yielded the vibrational spectrum corresponding toX ¹Σ⁺(0 _g ⁺ )→B ³Π(0 _g ⁺ ) transition up to the convergence limit. The photo-acoustic spectrum in the region 17580–18850 cm⁻¹ is presented along with the vibrational analysis. Five of the vibrational bands reported earlier by Venkateswarlu, Kumar and McGlynn have been partially resolved and the structure of one of them has been analyzed and shown to be due to an overlap of (14, 2) and (12, 1) bands. The analysis was based on a comparison with the highly resolved spectrum of Gerstenkorn and Luc. The structure observed in the region 20200–20750 cm⁻¹ which is beyond the convergence limit of the transitionX ¹Σ⁺(0 _g ⁺ )→B ³Π(0 _u ⁺ ) has been analyzed as due to two-photon absorption. Most of the bands could be assigned to two transitions both originating in the ground state and terminating in two different electronic states 1 _g andE(0 _g ⁺ ), atT _e=40821 cm⁻¹ (orT ₀=41355 cm⁻¹) andT _e=41411 cm⁻¹ (orT ₀=41355 cm⁻¹) respectively.     

Investigation of temperature-dependent electrical properties of p-VOPc/n-si heterojunction under dark conditions

An organic/inorganic heterojunction p-VOPc/n-Si was fabricated and its electrical properties were investigated. Temperature-dependent dark current–voltage (I–V) characteristics of the heterojunction exhibited rectification behaviour with a rectification ratio of 405 at ±1 V and room temperature. The current–voltage characteristics of the cell showed ohmic conduction at low voltages followed by a space charge-limited current (SCLC) conduction dominated by an exponential trap distribution at higher voltages. At room temperature, the series and shunt resistances were found to be approximately 1.4 and 100 kΩ, respectively. Diode ideality factor n was found to be 3.2 at room temperature and dropped to 1.9 at 363 K. Room temperature mobility of vanadyl phthalocyanine (VOPc) was extracted from the I–V characteristics in the SCLC region and was found approximately 15.5 × 10⁻³ cm² V⁻¹ s⁻¹. The effective barrier height, Ф_B, was estimated as 0.77 eV. The effect of temperature, on various heterojunction parameters was recorded under dark conditions and at temperatures ranging from 300 to 363 K.     

Improved measurement of theB0 andB+ meson lifetimes

The lifetimes of theB ⁰ andB ⁺ mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB ⁰ andB ⁺ mesons were partially reconstructed by identifying events containing a lepton with an associatedD*⁻ or meson. The second method used fully reconstructedB ⁰ andB ⁺ mesons. The third method, used to measure theB ⁰ lifetime, employed a partial reconstruction technique to identifyB ⁰→D*⁻ π ⁺ X decays.     

NMR-ON measurements of187WFe,182,183,186ReNi,186ReFe and203PbFe

The magnetic hyperfine splitting frequencies of¹⁸⁷WFe,¹⁸²Re(j ^π=2⁺)Ni,¹⁸³ReNi,¹⁸⁶ReNi,¹⁸⁶ReFe and²⁰³PbFe in a zero external magnetic field have been determined by the NMR-ON method at about 7 mK as 225.56(6), 130.9(1), 98.17(4), 136.6(4), 1007.0(3) and 58.43(3) MHz, respectively. With the knowng-factors ofg(¹⁸⁶Re, 1⁻)=1.739(3) andg(²⁰³Pb, 5/2⁻)=0.27456(20), the following hyperfine fields were deduced:B _HF(¹⁸⁶ReNi)=−103.05(35) kG;B _HF(¹⁸⁶ReFe)=−759.7(13) kG;B _HF(²⁰³PbFe)=+279.18(25) kG. Taking hyperfine anomalies into account, theg-factor of¹⁸³Re was deduced as |g(¹⁸³Re, 5/2⁺)|=1.267(6). With the assumption of Knight shift factorK=0, theg-factors of¹⁸²Re and¹⁸⁷W and the hyperfine field of¹⁸⁷WFe were determined as |g(¹⁸²Re, 2⁺)|=1.63(5), |g(¹⁸⁷W, 3/2⁻)|=0.414(10) andB _HF(¹⁸⁷WFe) =−714(18) kG. The large hyperfine anomaly was deduced to be¹⁸³W Δ¹⁸⁷W =−0.124(22).     

Hypervirial perturbation theory for eigenenergies for two types of atomic potentials

Eigenenergies are calculated for the potentialsV ₁(r)=−(a/r)[1+(1+br)e^−2br ] andV ₂(r)=−(v/r)[1 −λr(1−Z ⁻¹)(1+λr)⁻¹], using renormalized series technique. Accurate results produced here for various eigenstates agree with those available in the literature.     

Optical absorption spectrum of Ni2+ doped in ammonium zinc sulphate

The optical absorption spectrum of Ni²⁺ ion doped in ammonium zinc sulphate has been studied at room and liquid air temperatures. From the nature and the positions of the bands a successful interpretation of all the bands could be made assumingO _h symmetry for the Ni²⁺ ion in the crystal. The fine splitting of the³ T ₁ ¹ band at liquid air temperature has been successfully interpreted to be due to spin-orbit interaction. The crystal field and spin-orbit parameters derived areDq=1000 cm⁻¹;B=750 cm⁻¹;C=3.45B andξ=600 cm⁻¹.     

Conservation laws for classical and relativistic collisions. II

On the basis of elementary symmetry arguments it is shown that (1) if in classical mechanics there exists a quantity λ+Σ_iμ_iυ_i+1/2νυ ² that is conserved, where λ,μ _i, andν are particle parameters, then theμ _i andν are all proportional to a single parameterμ and the quantityAμ+Σ_iB_iμυ_i+C(λ+ 1/2Dμυ ²), whereD ≡ν/μ, is conserved for all values ofA, B _i, andC; (2) if in relativistic mechanics there exists a quantity λ+Σ_iμ_iυ_i[1−(υ ²/c ²)]^−1/2+νc[1−(υ ²/c ²)]^−1/2 that is conserved, then theμ _i andν are all proportional to a single parameterμ and the quantityAλ+Σ_iB_iμν_i[1−(υ ²/c ²)]^−1/2+Cμc [1−(υ ²/c ²)]^−1/2 is conserved for all values ofA, B _i, andC.     

Thin porous anodic alumina films: Interface trap density determination

The electrical properties of thin porous alumina films in the form of MOS structures were studied with dielectric spectroscopy at room temperature. The thickness of the samples was found to be approximately 95 nm with a cross section area of 1.6×10⁻³ cm².C-V andG-V measurements were performed by applying a loop sweep voltage 2.0 V to −5.0 V. Correction to the measurements were performed by considering a series resistanceR _S and leakage currentI _DC. TheC-V results show hysteresis effects due to the presence of positive charges in porous alumina. These charges may be are attributed to the residual electrolyte during the anodization process in the sample preparation. Three distinct regions in theC-V results are observed, namely the inversion, the depletion and the accumulation regions. In the voltage region, where depletion of carriers is observed,C-f andG-f measurements were recorded in the frequency range 1 Hz to 10⁶ Hz. The conductance method was applied for the calculation of the density D_it of carriers, trapped in the interface between insulator and semiconductor, and of the response time τ_it as a function of the applied bias voltage were performed. The values obtained for D_it and τ_it are of the order of 3×10¹² eV⁻¹ cm⁻² and 10⁻³ s, respectively, and they are voltage dependent. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Final-state polarization in <Emphasis Type="Italic">B</Emphasis><Stack><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript><Superscript>0</Superscript></Stack> decays

Certain B _s ⁰→V ₁ V ₂ decays (V _i is a vector meson) can be related by flavor SU(3) symmetry to corresponding B _d ⁰→V ₃ V ₄ decays. In this paper, we show that the final-state polarization can be predicted in the B _s ⁰ decay, assuming polarization measurements of the B _d ⁰ decay. This can be done within the scenario of penguin annihilation (PA), which has been suggested as an explanation of the unexpectedly large transverse polarization in B→φ K ^*. PA is used to estimate the breaking of flavor SU(3) symmetry in pairs of decays. Two of these for which PA makes a reasonably precise prediction of the size of SU(3) breaking are (B _s ⁰→φ φ,B _d ⁰→φ K ^0*) and ( ). The polarization measurement in the B _d ⁰ decay can be used to predict the transverse polarization in the B _s ⁰ decay and will allow for testing of PA as well as the other assumptions in the analysis.     

Properties of superconducting Nb/Al/Nb/Al?AlOx?Al?AlOx?Al/Nb/Al/Nb tunnel junctions

Modified geometry (MG) devices, Nb/Al/Nb/Al−AlO_x−Al−AlO_x−Al/Nb/Al/Nb, have been fabricated and investigated in comparison with the basic geometry (BG) double-barrier Nb/Al−AlO_x−Al−AlO_x−Al/Nb devices. The enhancement of the critical temperature in the Al film is found to be weaker for the MG devices as compared with the BG devices at temperatures nearT=4.2 K but stronger at lowT. Indication of an enhancement of dc Josephson critical current density,j _c , at bias voltageV≠0 as compared withj _c (V=0) has been observed in the MG devices for the first time.     

Effect of mean-square amplitude of atomic vibrations on the creep behaviour of cubic crystals

Correlation between the activation energyQ of high-temperature creep and the Debye-Waller thermal parameterB, which is proportional to the mean-square amplitude of atomic vibrations, has been examined in the case of 17 faced-centred cubic, body-centred cubic and diamond-structure cubic elements. It is observed thatQ is a function ofB, irrespective of the crystal structure;Q decreases asB increases. The correlation is governed by the power-lawQ=Q ₀(B/B ₀) ^M0 , whereQ ₀=0.095eV andM ₀=−0.62 are numerical constants determined by least-squares fit method, and the constantB ₀=1 nm².     

Combustion synthesis and luminescent properties of green-emitting phosphor (Sr, Zn) Al2O4: Eu2+, B3+ for white light emitting diodes (WLED)

In this study, the phosphors (Sr_1−x , Zn _x )_0.9(Al_2−y , B _y )O₄ doped 10 mol % Eu²⁺, were prepared by combustion method as the fluorescent material for white light emitting diodes (WLEDs), performing as a light source. The luminescent properties were investigated by changing the combustion temperature, the boron concentration, and the ratio of Sr to Zn. The luminescence, crystallinity and particle morphology were investigated by using a luminescence spectrometer, X-ray diffractometer (XRD) and transmission electron microscopy (TEM), respectively. The highest intensity of Sr_0.9(Al_2−y , B _y )O₄: Eu_0.1²⁺ phosphor was achieved when the combustion temperature was 600° and the concentration of B³⁺ was 8 mol % of the aluminate. A new blue emission was observed when the high Zn concentration (x ⩾ 0.8), and this blue emission disappeared with the Zn concentration became lower than 0.8. The combustion method synthesized phosphor (Sr_0.6, Zn_0.4)_0.9(Al_1.92, B_0.08)O₄: Eu_0.1²⁺ showed 3.3 times improved emission intensity compared with that of the Sr_0.9(Al_1.92, B_0.08)O₄:Eu_0.1²⁺ phosphor under λ _ex = 390 nm.      

ESR study of exchange coupled pairs in copper diethyldithiocarbamate

ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)₂, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g _‖=2.1025,g ₊=2.031,A=75.1×10⁻⁴ cm⁻¹,B=14.8×10⁻⁴,D=276.0×10⁻⁴ cm⁻¹ andE=46.7×10⁻⁴ cm⁻¹. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm⁻¹. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)₂—direct exchange and superexchange through the bridging sulphurs—are discussed.     

EPR of manganese-containing plasticine: Spectral simulation and use as an internal standard for comparison of the signal intensities of various free-radical EPR spectra

Electron paramagnetic resonance spectra of manganese-containing plasticine putty have been obtained both at 9.4 and 94.2 GHz (room temperature). It has been possible to analyze both, quantitatively by computer-based simulation and exact diagonalization of a general spin-Hamiltonian, by use of an appropriate powder technique. A fine fit was obtained for both frequencies with an isotropicg-2.00117, uniaxial⁵⁵Mn hyperfine valuesA _∥/g _c β _c = −93.5 G (where ‖ implies direction (ℤ) andA _⊥/g _c β _c = −94.3 G, a nuclear quadrupole effectP _z(⁵⁵Mn)=0, and a uniaxial electronic quadrupole matrix (D/g _c β _c = 3D _Z/2g _c β _c = −82.8 G). The electronic octupole energy was taken into account via the single parameterB ₄⁰/g _c β _c = −0.024 G. The plasticine has been demonstrated to afford a fine intensity and magnetic-field standard, say, for use with free radicals such as spin-trap adducts. Examples provided are 2,2-diphenyl-l-picrylhydrazyl, and hydroxyl radical generated by the Fenton reaction and spin-trapped with 5,5-dimethyl-1-pyroline-N-oxide.