Effect of cation mixing on luminescence of Eu in SrCl2

SrCl₂ forms solid solutions of various compositions with BaCl₂ and CaCl₂. Orthorhombic and tetragonal phases are also known to occur in the SrCl₂-CaCl₂ system. Though efficient emission of Eu²⁺ in SrCl₂ and CaCl₂ is known, there are no reports available on Eu²⁺ luminescence in the solid solutions and other phases. Investigations on these lines were carried out and the results are presented in this paper. Very intense emission comparable to that of the commercial lamp phosphors was observed for the solid solutions while the intensities for the orthorhombic and tetragonal phases are an order of magnitude smaller. Emission wavelengths do not vary much while excitation spectra for the solid solutions are much enhanced in the near UV region (350-400 nm). It is suggested that these results will be significant for developing phosphors with near UV excitations needed in applications such as solid state lighting.     

Growth of ultrathin layers of Au on LiNbO3(0 0 0 1) measured with atomic force microscopy

Atomic force microscopy (AFM) has been used to characterize the growth of Au deposited via evaporation onto the positive face of single crystalline, lithium niobate, LiNbO₃(0 0 0 1) surface. In order to study the mechanisms for the ordering and aggregation of a noble metal on this ferroelectric surface, topographic and phase contrast imaging of the fractional surface coverage of Au were performed. Atomically flat, uniformly poled LiNbO₃ surfaces were prepared via an ambient high temperature anneal and served as a support for the thin gold films. These gold atomic layers were grown using electron bombardment evaporation sources under ultra-high vacuum (UHV) conditions and subsequently characterized under both vacuum and ambient environments. Using AFM it was found that gold preferentially nucleates at the top of LiNbO₃ substrate step edges. With increased coverage, island formation proceeds due to local aggregation of adsorbed gold on each substrate terrace. Based on local imaging of the growth morphology, the data is discussed in terms of thin film growth mechanisms as well as the influence of native surface features such as defects and charge distribution. Understanding growth mechanisms for gold layers on ferroelectric surfaces allows for a fuller appreciation of how atomic deposition of metal atoms on patterned poled LiNbO₃ surfaces would occur as well as yielding greater insight on the atomic characteristics of metals on ferroelectric interfaces.     

Combustion synthesis of Sr3MgSi2O8:Eu and Sr2MgSi2O7:Eu phosphors

Sr₃MgSi₂O₈:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺ phosphors find uses in applications such as plasma display panel (PDP), solid-state lighting, longafter glow. Preparation of these phosphors by a modified combustion synthesis is described in this paper. As-prepared samples did not show photoluminescence. After reducing the samples at 900 °C, characteristic Eu²⁺ emission was observed. Preparation of these phosphors by using similar methods helped clarifying various results obtained for Sr₃MgSi₂O₈:Eu²⁺ by different investigators.     

The Higgs mass beyond the CMSSM

The recent discovery of a new boson at the LHC, which resembles a SM-like Higgs boson with m _h =125 GeV, is starting to provide strong guidelines into SUSY model building. For instance, the identification of such a state with the lightest CP-even Higgs boson of the MSSM (h ⁰), requires large values of tanβ and/or heavy sfermions. One outcome of this result is the possibility to solve the SUSY flavor and CP problems by decoupling, which points towards some realization of Split-inspired SUSY scenarios, in which scalars are much heavier than gauginos and higgsinos. However, we argue here that the remaining Higgs bosons of the MSSM (H ⁰, A ⁰, H ^±) do not have to be as heavy as the sfermions, and having them with masses near the EW scale does not pose any conflict with current MSSM constraints. We discuss then some SUSY scenarios with heavy sfermions, from a bottom-up approach, which contain the full Higgs sector, as well as a possible dark matter candidate, with masses near the EW scale, and identify distinctive signals from these scenarios that could be searched at the LHC.     

Effects of a Vocally Fatiguing Task and Systemic Hydration on Men''s Voices

Voice disorders, specifically vocal fatigue, are more commonly reported by women than by men. Previously, 4 women with normal untrained voices read loudly for 2 hours in an attempt to fatigue the voice. Vocal function deteriorated, as indicated by increases in phonation threshold pressure (PTP) and self-perceived phonatory effort. The increase in PTP was delayed or attenuated to some degree in 3 of the women when they drank ample amounts of water before the experiment. The current study examined the same vocal-loading task and water-drinking condition in 4 vocally normal men. PTP increased after the loud-reading task. Although 2 of the men appeared to benefit from increased systemic hydration (PTP increased more when they were underhydrated than well-hydrated), the other 2 men's data changed in the opposite direction. Phonatory effort correlated well with PTP; this varied across subject and pitch. Laryngeal endoscopy revealed an anterior glottal gap in two men after the loud-reading task. Amplitude of vocal fold vibration was judged to be reduced after the loud-reading task in three subjects when underhydrated and one subject when well hydrated. The high between-subject variability prohibits a conclusion that drinking water is beneficial to vocal function in men, but all subjects studied to date demonstrated detrimental vocal effects of prolonged loud talking.     

Synthesis and effect of Ce co-doping on photoluminescence characteristics of KZnSO4Cl: M (M=Dy or Mn) new phosphors

In the present paper KZnSO₄Cl:Ce³⁺, KZnSO₄Cl:Ce³⁺, Dy³⁺ and KZnSO₄Cl:Ce³⁺, Mn²⁺ new halosulfate phosphors were synthesized by wet chemical method. XRD and photoluminescence characterization of phosphors has been reported in this paper.     

Preparation of CaF2 based phosphors by solid state metathesis

Synthesis of CaF₂:Eu and CaF₂:Ce phosphors by solid state metathesis is reported for the first time. CaF₂ could be prepared in few minutes using domestic microwave oven. Though CaF₂ is formed by metathesis, luminescence centres were not formed in one step; as-prepared samples did not show any luminescence. Samples reduced at 1000 °C for 1 h exhibited very intense, characteristic emission. Activator concentration, and in turn, the intensity of luminescence depends on the partition coefficient of the activator in the host and the washable reaction products (KCl in the present case). In case of Europium, most of the activator is retained by CaF₂ while for Cerium a significant fraction of the added activator is washed away with KCl.     

A new characterization of graphs based on interception relations

While graphs are normally defined in terms of the 2-place relation of adjacency, we take the 3-place relation of interception as the basic primitive of their definition. The paper views graphs as an economical scheme for encoding interception relations, and establishes an axiomatic characterization of relations that lend themselves to representation in terms of graph interception, thus providing a new characterization of graphs. © 1996 John Wiley & Sons, Inc.     

Application of the distinguishable electron method

In order to make a better assessment of the distinguishable electron method developed by Kirtman and co-workers, we have applied the method to some two-electron atoms and to H₂ and LiH. Our results lend support to the contention held by Kirtman and co-workers that the distinguishable electron method is a practical way of calculating reasonably accurate physical properties.