Spectroscopic investigations and luminescence spectra of Nd3+ and Dy3+ doped different phosphate glasses

Spectral properties of Nd3+ and Dy3+ ions in different phosphate glasses were studied and several spectroscopic parameters were reported. Covalency of rare-earth-oxygen bond was studied in these phosphate glass matrices with the variation of modifier in host glass matrix Using Judd-Ofelt intensity parameters (Omega(2), Omega(4) and Omega(6)), radiative transition probabilities (A) and radiative lifetimes (tau(R)) of certain excited states of Nd3+ and Dy3+ ions are estimated in these glass matrices. From the magnitudes of branching ratios (beta(R)) and integrated absorption cross-sections (Sigma), certain transitions of both the ions are identified for laser excitation. From the emission spectra, peak stimulated emission cross-sections (sigma(P)) are evaluated for the emission transitions observed in all these phosphate glass matrices for both Nd3+ and Dy3+ ions. (C) 2009 Elsevier B.V. All rights reserved.

Free-to-bound and bound exciton transitions at isoelectronic impurities: GaP(Zn,O)

We show, for sufficiently high temperatures and sufficiently weak majority-carrier binding energies, that the dominant radiative transition at an isoelectronic acceptor (donor) in p-type (n-type) material consists of the recombination of singly trapped minority carriers (bound by central-cell forces) with free majority carriers attracted by a Coulomb interaction. There are two reasons why the radiative recombination rate of the free-to-bound process is greater than the bound exciton process, which dominates at lower temperatures: (i) The population of free majority-carrier states greatly exceeds that of exciton states at higher temperatures, and (ii) the oscillator strength of the free-to-bound transition is greatly enhanced by the Coulomb attraction between the free carrier and the charged isoelectronic impurity. This enhancement is important for isoelectronic centers and is easily calculable from existing exciton models. We show that the free carrier attracted by a Coulomb interaction can be viewed as a continuum excited state of the bound exciton. When we apply the results of our calculations to the GaP(Zn, O) system, we find that the major part of the room-temperature luminescence from nearest-neighbor isoelectronic Zn-O complexes results from free-to-bound recombination and not exciton recombination as has been thought previously. Recent experiments on impulse excitation of luminescence in GaP(Zn, O) are reevaluated in the light of our calculations and are shown to be consistent with a strong free-to-bound transition. For deep isoelectronic centers with weakly bound majority carriers, we predict an overwhelming dominance of the free-to-bound process at 300°K.

Studies on optical absorption and photoluminescenceproperties of Pr3+ and Nd3+ doped mixed alkali chloroborate glasses

This article presents the optical absorption and emission properties of Pr3+ and Nd3+ doped two different mixed alkali chloroborate glass matrices of the type 70B(2)O(3)center dot xLiCl center dot(30 - x)NaCl and 70B(2)O(3)center dot xLiCl center dot(30 - x)KCl (x = 5, 10, 15.20 and 25). The variation of Judd-Ofelt parameters (Omega(2), Omega(4) and Omega(6)), total radiative transition probabilities (A(T)), radiative lifetimes (tau(R)) and emission cross-sections (sigma(p)) with the variation of alkali contents in the glass matrix have been discussed in detail. The changes in the peak wavelengths of the hypersensitive transition and intensity parameters with x are correlated to the structural changes in the host matrix. The estimated radiative lifetimes of certain excited states of Pr3+ and Nd3+ in these two glass matrices are reported. Peak stimulated emission cross-sections (sigma(p)) are reported for the observed emission transitions of Pr3+ and Nd3+ ions. Branching ratios (beta) of the observed emission transitions obtained from the Judd-Ofelt theory are compared with the values obtained from the emission spectra. (C) 2010 Elsevier B.V. All rights reserved.

The effect of host glass on optical absorption and fluorescence of Nd3+ in xNa(2)O-(30-x)K2O-70B(2)O(3) glasses

The effect of host glass composition on the optical absorption and fluorescence spectra of Nd3+ has been studied in mixed alkali borate glasses of the type xNa(2)O-(30-x)K2O-69.5B(2)O(3)-0.5Nd(2)O(3) (X = 5,10,15,20 and 25). Various spectroscopic parameters such as Racah (E-1, E-2 and E-3), spin-orbit (xi(4f)) and configuration interaction (alpha, beta) parameters have been calculated. The Judd-Ofelt intensity parameters (Omega(lambda)) have been calculated and the radiative transition probabilities (A(rad)), radiative lifetimes (tau(r)), branching ratios (beta) and integrated absorption cross sections (Sigma) have been obtained for certain excited states of the Nd3+, ion and are discussed with respect to x. From the fluorescence spectra, the effective fluorescence line widths (Deltalambda(eff)) and stimulated emission cross sections (sigma(p)) have been obtained for the three transitions F-4(3/2) --> I-4(9/2), F-4(3/2) --> I-4(11/2) and F-4(3/2) --> I-4(13/2) of Nd3+. The stimulated emission cross section (sigma(p)) values are found to be in the range (2.0-4.8) x 10(-2)0 cm(2) and they are large enough to indicate that the mixed alkali borate glasses could be potential laser host materials.

The fluorescence of Nd3+ in lead borate and bismuth borate glasses with large stimulated emission cross section

The stimulated emission cross section σp for the 1060 nm transition of Nd3+ in lead borate and bismuth borate glasses has been determined from fluorescence measurements. The compositional dependence of σp, which has been evaluated using radiative transition probability, refractive index of the host glass, effective fluorescence linewidth, and position of the band, with PbO/Bi2O3 content is investigated. The σp values of the 1060 nm band of Nd3+ for lead borate and bismuth borate glasses are found to be in the range 2.6–5.7×10−20 cm2 at 298 K and 3.0–6.3×10−20 cm2 at 4.2 K. The σp values are comparatively large suggesting the possible utilization of these materials in laser applications.

Electric field induced short range to long range structural ordering and its influence on the Eu+3 photoluminescence in the lead-free ferroelectric Na1/2Bi1/2TiO3

Eu+3 was incorporated into the lattice of a lead-free ferroelectric Na1/2Bi1/2TiO3 (NBT) as per the nominal formula Na0.5Bi0.5-xEuxTiO3. This system was investigated with regard to the Eu+3 photoluminescence (PL) and structural behaviour as a function of composition and electric field. Electric field was found to irreversibly change the features in the PL spectra and also in the x-ray diffraction patterns below the critical composition x = 0.025. Detailed analysis revealed that below the critical composition, electric field irreversibly suppresses the structural heterogeneity inherent of the host matrix NBT and brings about a long range ferroelectric state with rhombohedral (R3c) distortion. It is shown that the structural disorder on the nano-scale opens a new channel for radiative transition which manifests as a new emission line branching off from the main D-5(0)-> F-7(0) line along with a concomitant change in the relative intensity of the other crystal field induced Stark lines with different J values. The study suggests that Eu+3 luminescence can be used to probe the relative degree of field induced structural ordering in relaxor ferroelectrics and also in high performance piezoelectric alloys where electric field couples very strongly with the lattice and structural degrees of freedom. (C) 2015 AIP Publishing LLC.

Aerosol characteristics and radiative impacts over the Arabian Sea during the intermonsoon season: Results from ARMEX field campaign

During the second phase of the Arabian Sea Monsoon Experiment (ARMEX-II), extensive measurements of spectral aerosol optical depth, mass concentration, and mass size distribution of ambient aerosols as well as mass concentration of aerosol black carbon (BC) were made onboard a research vessel during the intermonsoon period (i.e., when the monsoon winds are in transition from northeasterlies to westerlies/ southwesterlies) over the Arabian Sea (AS) adjoining the Indian Peninsula. Simultaneous measurements of spectral aerosol optical depths (AODs) were made at different regions over the adjoining Indian landmass. Mean AODs (at 500-nm wavelength) over the ocean (similar to0.44) were comparable to those over the coastal land (similar to0.47), but were lower than the values observed over the plateau regions of central Indian Peninsula (similar to0.61). The aerosol properties were found to respond distinctly with respect to change in the trajectories, with higher optical depths and flatter AOD spectra associated with trajectories indicating advection from west Asia, and northwest and west-coastal India. On average, BC constituted only similar to2.2% to total aerosol mass compared to the climatological values of similar to6% over the coastal land during the same season. These data are used to characterize the physical properties of aerosols and to assess the resulting short-wave direct aerosol forcing. The mean values were similar to27 W m(-2) at the surface and -12 W m(-2) at the top of the atmosphere (TOA), resulting in a net atmospheric forcing of +15 W m(-2). The forcing also depended on the region from where the advection predominates. The surface and atmospheric forcing were in the range -40 to -57 W m(-2) and +27 to +39 W m(-2), respectively, corresponding to advection from the west Asian and western coastal India where they were as low as -19 and +10 W m(-2), respectively, when the advection was mainly from the Bay of Bengal and from central/peninsular India. In all these cases, the net atmospheric forcing (heating) efficiency was lower than the values reported for northern Indian Ocean during northern winter, which is attributed to the reduced BC mass fraction.

Transition from disc to rod-like shape of 16-3-16 dimeric micelles in aqueous solutions

Small-angle neutron scattering (SANS) measurements from bis-cationic C16H33N+(CH3)(2)-(CH2)(3)-N+ (CH3)(2)C16H33 2Br(-) dimeric surfactant, referred to as 16-3-16, at different concentrations and temperatures, are reported. It is seen that micelles are disc-like for concentrations C = 2.5 and 10 mM at temperature T = 30 degrees C. At low concentration C = 0.5 mM micelles are rod-like. Similarly, there is a disc to rod-like transition of micelles on increasing the temperature. For C = 2.5 mM, micelles are rod-like at T = 45 and 70 degrees C.

Universality in the fast orientational relaxation near isotropic-nematic transition

Detailed molecular dynamics simulations of Lennard-Jones ellipsoids have been carried out to investigate the emergence of criticality in the single-particle orientational relaxation near the isotropic-nematic (IN) phase transition. The simulations show a sudden appearance of a power-law behavior in the decay of the second-rank orientational relaxation as the IN transition is approached. The simulated value of the power-law exponent is 0.56, which is larger than the mean-field value (0.5) but less than the observed value (0.63) and may be due to the finite size of the simulated system. The decay of the first-rank orientational time correlation function, on the other hand, is nearly exponential but its decay becomes very slow near the isotropic-nematic transition, The zero-frequency rotational friction, calculated from the simulated angular Velocity correlation function, shows a marked increase near the IN transition.

Unoccupied electronic states in NiS2-xSex across the metal-insulator transition

We investigate the evolution of the electronic structure across the insulator-metal transition in NiS2-xSex with changing composition, but in the absence of any structural or magnetic changes. A comparison of the inverse photoemission spectra with band-structure calculations establishes the importance of correlation effects in these systems. Systematic changes in the spectral distribution establish the persistence of the upper Hubbard band well into the metallic regime, with the insulator-to-metal transition being driven by a transfer of spectral weight from the Hubbard band to states close to the Fermi energy.

High-Temperature Phase Transition Studies in a Novel Fast Ion Conductor, Na2Cd(SO4)2, Probed by Raman Spectroscopy

Temperature-dependent Raman spectroscopic studies were carried out on Na2Cd(SO4)(2) from room temperature to 600 degrees C. We observe two transitions at around 280 and 565 degrees C. These transitions are driven by the change in the SO4 ion. On the basis of these studies, one can explain the changes in the conductivity data observed around 280 and 565 degrees C. At 280 degrees C, spontaneous tilting of the SO4 ion leads to restriction of Na+ mobility. Above 565 degrees C, the SO4 ion starts to rotate freely, leading to increased mobility of Na+ ion in the channel.

New main group ligands for complexation with transition and inner transition elements

Symmetrical and unsymmetrical diphosphinoamines of the type X(2)PN(R)PX(2) and X(2)PN(R)YY' offer vast scope for the synthesis of a variety of transition metal organometallic complexes. Diphosphinoamines can be converted into their dioxides which are also accessible from appropriate (chloro)phosphane oxide precursors. The diphosphazane dioxides form an interesting series of complexes with lanthanide and actinide elements. Structural and spectroscopic studies have been carried out on a wide range of transition metal complexes incorporating linear P-N-P ligands and judiciously functionalized cyclophosphazanes and cyclo-phosphazenes.

Lowering of relaxor transition temperature in Lead-based perovskites under pressure

The dielectric constants of lead iron niobate (PFN) and 40% lead zinc niobate (PZN) added to lead iron niobate (PFN0.6-PZN(0.4)) have been measured as a function of pressure up to 6 GPa under isothermal conditions between room temperature and 348 K. The relaxer transition temperature measured at 1 kHz excitation frequency varies at a rate -24.5 K/GPa for PFN and at a rate of - 28.8 K/GPa for the PFN0.6-PZN(0.4) composition.

Metal-Ion-Dependent Oxidative DNA Cleavage by Transition Metal Complexes of a New Water-Soluble Salen Derivative

A new water-soluble, salen [salen = bis(salicylidene) ethylenediamine]-based ligand, 3 was developed. Two of the metal complexes of this ligand, i.e., 3a, [Mn(III)] and 3b, [Ni(II)], in the presence of cooxidant magnesium monoperoxyphthalate (MMPP) cleaved plasmid DNA pTZ19R efficiently and rapidly at a concentration similar to 1 mu M. In contrast, under comparable conditions, other metal complexes 3c, [Cu(II)] or 3d, [Cr(III)] could not induce any significant DNA nicking. The findings with Ni(II) complex suggest that the DNA cleavage processes can be modulated by the disposition of charges around the ligand.

Transition metal complexes of a potential anticancer quinazoline ligand

A new heterocycle, namely 2-(furyl)-3-(furfuralimino)-1,2-dihydroquinazolin-4(3H)-one (ffdq) was formed by the ondensation of 2-aminobenzoylhydrazide with furfural and characterized by physico-chemical, spectroscopic, and single crystal X-ray diffraction studies. A series of complexes of ffdq have been synthesized and characterized by physico-chemical, spectroscopic, and thermal studies. According to the i.r. and 1H-n.m.r. spectra ffdq behaves as a bidentate ligand coordinating through quinazoline oxygen and azomethine nitrogen. The FAB-mass spectrum of the Cd(II) complex indicates the monomeric nature of this complex. The X-band e.p.r. spectrum of the Cu(II) complex and thermal stabilities of the Co(II) and Ni(II) complexes are discussed.