Epitaxial growth and spectroscopic investigation of hexavalent manganese in barium sulfate

We investigate the influence of active-ion distributions on energy-transfer upconversion (ETU) in a static upconversion regime in which energy migration is inactive and the active local environment is important for the dynamics of ETU. Neodymium is used as the probe ion. In oxide and fluoride host materials, Nd3+ possesses only one metastable excited state (4F3/2) from which strong ETU occurs. The levels excited by ETU emit weak visible luminescence, possess short (multiphonon-quenched) lifetimes and, therefore, react almost instantaneously on the dynamics of the metastable level. The chosen host material lanthanum scandium borate [1] possesses large distances between the active-ion sites and ETU occurs in the static regime [2,3]. After excitation of the metastable level, we measure concentration-dependent (10, 25, 50, 100 at.%) infra-red (direct) and visible (upconversion) luminescence decay. The upconversion luminescence decays neither quadratically with respect to the direct luminescence as would be expected from a usual rate-equation model -- even if two classes of isolated (non-ETU) and clustered (ETU) ions are assumed [4] -- nor exponentially as would be expected from a dimer model [5]. The decay curves are described in a multimer model that takes into account the real structure of the host material and assumes centers with different numbers of active nearest neighbors. With decreasing excitation at longer decay times, its solution converges to the solution of a quasi-dimer model.\ud [1] J.P. Meyn et al., IEEE J. Quantum Electron. 30, 913 (1994)\ud [2] D.A. Zubenko et al., Phys. Rev. B 55, 8881 (1997)\ud [3] V. Ostroumov et al., J. Opt. Soc. Am. B 15, 1052 (1998)\ud [4] M. Pollnau, J. Alloys Compd. 341, 51 (2002)\ud [5] D.R. Gamelin, H.U. Güdel, in Topics in Current Chemistry, Vol. 214 (Springer-Verlag, Berlin Heidelberg, 2001

Flux growth and liquid phase epitaxy of undoped and Mn6+-doped sulfates, tungstates, and molybdates

The Mn6+ ion is a promising activator ion for tunable and short-pulse laser materials because of its broadband luminescence in the spectral region 850-1600 nm and its simple 3d1 electronic configuration, which excludes an occurrence of undesirable exited-state absorption into higher 3d levels. However, hexavalent manganese can be stabilized only in the tetrahedral oxo-coordination and easily reduces to Mn5+ or Mn4+ at temperatures above 600°C. Recently, flux [1] and liquid-phase epitaxy (LPE) [2] growth of Mn6+-doped sulfates has been reported, while except for BaMoO4:Mn6+ [3] investigations on the mechanically more stable alkaline-earth-metal molybdates and tungstates as possible host materials for efficient Mn6+ incorporation have as yet not been reported.\ud We investigated the growth conditions of undoped and Mn6+-doped MAO4, with M = Ca, Sr, Ba and A = S, Mo, W, from the ternary NaCl-KCl-CsCl solvent at temperatures 480-600°C. The growth rates increase in the series tungstates < molybdates < sulfates and depending on the cation, in the series Ca < Sr < Ba. The dopant ion Mn6+ can be easily incorporated into BaSO4, less well into BaMoO4 and BaWO4, whereas for Ca- and Sr-containing tungstates and molybdates no significant doping was found, independent on the concentration of Mn6+ in the liquid solution. Moreover, reduction of the Mn6+ ion cannot be avoided, even at the presence of oxidizing additives such as K2CO3 or NaOH.\ud LPE was employed for growing Mn6+-doped layers of BaAO4 compounds. Growth velocities of 3-5 µm/h in the temperature interval from 490-540°C from chloridic solution, containing 0.3-1mol% of K2MnO4 with respect to the solute, delivered dark-pink BaSO4 and slightly green BaMoO4 and BaWO4 layers up to 200 µm in thickness. With respect to high Mn6+ doping levels, BaSO4 is the most suitable host material and its further investigation under different initial concentrations of manganese is currently underway.\ud \ud [1] T.C. Brunold, H.U. Güdel, Inorg. Chem. 36, 1946 (1997).\ud [2] D. Ehrentraut, M. Pollnau, Appl. Phys. B 75, 59 (2002).\ud [3] T.C. Brunold, H.U. Güdel, Chem. Phys. Lett. 249, 77 (1996)

Origin of the (2)E <->(4)T(2) Fano resonance in Cr(3+)-doped LiCaAlF(6): Pressure-induced excited-state crossover.

This work investigates pressure-induced phase transition (PT) and excited-state-crossover effects on the photoluminescence (PL) properties of LiCaAlF(6):Cr(3+). We report a PL study by means of time-resolved emission, excitation, and lifetime measurements as a function of pressure. We focus on Cr(3+) PL variations around pressure-induced trigonal-to-monoclinic first-order PT in LiCaAlF6 at 7 GPa. Moreover, the structural requirements for changing Cr(3+) PL from a broadband emission at 1.59 eV (781 nm) at ambient conditions, to a rubylike narrow-line emission at 1.87 eV (663 nm) are analyzed in the 0-35 GPa range. We show how pressure progressively transforms Cr(3+) broadband PL into a rubylike emission that becomes the dominant feature of the room-temperature emission spectrum at 28 GPa. This behavior, together with the pressure dependences of the (2)E and (4)T(2) excited-states energy and PL lifetime, are explained on the basis of the electron-phonon coupling associated with the (4)T(2) and (2)E states. We demonstrate that both excited states interact through spin-orbit coupling yielding Fano resonance rather than antiresonance as is frequently assumed

Core-log-seismic integration in metamorphic rocks and its implication for the regional geology: A case study for the ICDP drilling project COSC-1, Sweden

Continental collision causes deformation in the crust along shear zones. However, the physical and chemical conditions at which these zones operate and the deformation processes that enable up to hundreds of km of tectonic transport are still unclear because of the depth at which they occur and the challenges in imaging them. Ancient exhumed collision zones allow us to investigate these processes much better, for example at the COSC‐1 borehole in the central Scandinavian Caledonides. This study combines data from the COSC‐1 borehole with different seismic measurements to provide constraints on the spatial lithological and textural configuration of the Seve Nappe Complex. This is one of the few studies that shows that core‐log‐seismic integration in metamorphic rocks allows to identify the spatial distribution of major lithological units. Especially gamma ray logs in combination with density data are powerful tools to distinguish between mafic and felsic lithologies in log‐core correlation. Our results indicate that reflections along the borehole are primarily caused by compositional rather than textural changes. Reflections in the Seve Nappe Complex are not as distinct as in greater depths but continuous and several of them can be linked to magmatic intrusions, which have been metamorphically overprinted. Their setting indicates that the Seve Nappe Complex consists of the remnants of a volcanic continental margin. Our results suggest that ductile‐deformed middle crustal reflectivity is primarily a function of pre‐orogenic lithological variations which has to be considered when deciphering mountain building processes

Sexual reproduction and mating-type-mediated strain development in the penicillin-producing fungus Penicillium chrysogenum

Penicillium chrysogenum is a filamentous fungus of major medical and historical importance, being the original and present-day industrial source of the antibiotic penicillin. The species has been considered asexual for more than 100 y, and despite concerted efforts, it has not been possible to induce sexual reproduction, which has prevented sexual crosses being used for strain improvement. However, using knowledge of mating-type (MAT) gene organization, we now describe conditions under which a sexual cycle can be induced leading to production of meiotic ascospores. Evidence of recombination was obtained using both molecular and phenotypic markers. The identified heterothallic sexual cycle was used for strain development purposes, generating offspring with novel combinations of traits relevant to penicillin production. Furthermore, the MAT1-1–1 mating-type gene, known primarily for a role in governing sexual identity, was also found to control transcription of a wide range of genes with biotechnological relevance including those regulating penicillin production, hyphal morphology, and conidial formation. These discoveries of a sexual cycle and MAT gene function are likely to be of broad relevance for manipulation of other asexual fungi of economic importance

Improved Phylogenetic Analyses Corroborate a Plausible Position of Martialis heureka in the Ant Tree of Life

Martialinae are pale, eyeless and probably hypogaeic predatory ants. Morphological character sets suggest a close relationship to the ant subfamily Leptanillinae. Recent analyses based on molecular sequence data suggest that Martialinae are the sister group to all extant ants. However, by comparing molecular studies and different reconstruction methods, the position of Martialinae remains ambiguous. While this sister group relationship was well supported by Bayesian partitioned analyses, Maximum Likelihood approaches could not unequivocally resolve the position of Martialinae. By re-analysing a previous published molecular data set, we show that the Maximum Likelihood approach is highly appropriate to resolve deep ant relationships, especially between Leptanillinae, Martialinae and the remaining ant subfamilies. Based on improved alignments, alignment masking, and tree reconstructions with a sufficient number of bootstrap replicates, our results strongly reject a placement of Martialinae at the first split within the ant tree of life. Instead, we suggest that Leptanillinae are a sister group to all other extant ant subfamilies, whereas Martialinae branch off as a second lineage. This assumption is backed by approximately unbiased (AU) tests, additional Bayesian analyses and split networks. Our results demonstrate clear effects of improved alignment approaches, alignment masking and data partitioning. We hope that our study illustrates the importance of thorough, comprehensible phylogenetic analyses using the example of ant relationships

Towards a standard procedure for the measurement of the multi-photon component in a CW telecom heralded single-photon source

Single-photon sources are set to be a fundamental tool for metrological applications as well as for quantum information related technologies. Because of their upcoming widespread dissemination, the need for their characterization and standardization is becoming of the utmost relevance. Here, we illustrate a strategy to provide a quantitative estimate of the multi-photon component of a single-photon source, showing the results achieved in a pilot study for the measurement of the second order autocorrelation function $g^{(2)}$ of a low-noise CW heralded single-photon source prototype (operating at telecom wavelength $\lambda=1550$ nm) realized in INRiM. The results of this pilot study, involving PTB, NPL and INRiM, will help to build up a robust and unambiguous procedure for the characterization of the emission of a single-photon source