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The moss Physcomitrella patens, a model system for basal land plants, tolerates several abiotic stresses, including dehydration. We previously reported that Physcomitrella patens survives equilibrium dehydration to -13 MPa in a closed system at 91% RH. Tolerance of desiccation to water potentials below -100 MPa was only achieved by pretreatment with exogenous abscisic acid (ABA). We report here that gametophores, but not protonemata, can survive desiccation below -100 MPa after a gradual drying regime in an open system, without exogenous ABA. In contrast, faster equilibrium drying at 90% RH for 3-5 days did not induce desiccation tolerance in either tissue. Endogenous ABA accumulated in protonemata and gametophores under both drying regimes, so did not correlate directly with desiccation tolerance. Gametophores of a Ppabi3a/b/c triple knock out transgenic line also survived the gradual dehydration regime, despite impaired ABA signaling. Our results suggest that the initial drying rate, and not the amount of endogenous ABA, may be critical in the acquisition of desiccation tolerance. Results from this work will provide insight into ongoing studies to uncover the role of ABA in the dehydration response and the underlying mechanisms of desiccation tolerance in this bryophyte.

Microcrystalline silicon carbide alloys (μc-SiC:H) have attracted attention as a potential window layer for thin film silicon solar cells and silicon heterojunction solar cells. Thanks to the combination of high transparency and conductivity. At present, identification of electronically active impurities and defects is highly relevant for application of μc-SiC:H. Electron paramagnetic resonance has been successfully applied to investigate defects and impurities in crystalline SiC. Continuous wave X-band EPR measurements performed earlier on a number of μc-SiC:H samples show intensive and complex spectra with multiple overlapped components. In order to resolve components of the μc-SiC:H spectra, we performed a series of pulsed EPR measurements in S-, X-, and Q-band completed with a Q-band ENDOR experiment. The experiment was successful to resolve hidden complexity of the EPR spectra of μc-SiC:H and determine the nucleus responsible for the hyperfine pattern observed in previous studies.

Electronic transport and paramagnetic defects detected by Electron Spin Resonance (ESR) in both intrinsic and -type silicon oxide prepared by PECVD were investigated. The structure and alloy composition of the material were varied all the way from microcrystalline silicon (µc-Si:H) to amorphous silicon oxide (a-SiOX:H). The transition-phase-mixture material is called “microcrystalline silicon oxide” (µc-SiOX:H). In undoped samples we find a strong reduction of the dark conductivity from 10-3to 10-12 S/cm and an increase of the spin density from1017 to 3×1019 cm-3 as the crystallinity decreases from 80% to 0%. The variation of the dark conductivity in phosphorous doped samples was even higher from 101 to 10-12 S/cm. ESR spectra of intrinsic material consist of a single featureless line with g-values in the range of 2.0043…2.005 depending on the structure and alloying. The spectra of -type material exhibit a broader range of g-values of 1.998…2.0043 due to strong variations of the Fermi level over the entire crystallinity range. The results are discussed within the frame of current understanding of µc-SiOX:H as a phase mixture of µc-Si:H crystallites embedded in a-SiOX:H matrix (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GdTaO 4 :Eu 0.1 Zn x phosphors were synthesized by the conventional solid-state reaction. The effects of Zn 2+ ions on the crystallization behavior, morphology and photoluminescence (PL) properties of GdTaO 4 :Eu 3+ were investigated. The results indicate that the PL intensity of GdTaO 4 :Eu 3+ phosphor was improved remarkably by Zn 2+ doping. There were two maxima in PL intensity against Zn 2+ dopant concentration, one was improved up to 2.7 times at x = 0.01 and the other was enhanced up to 3.2 times at x = 0.13. The first maximum was regarded as the incorporation of Zn 2+ ions altering the local environment of activator Eu 3+ ions and the second maximum was due to the flux effect of Zn 2+ ions. And the phases of ZnO and GdTa 7 O 19 were observed in excessive Zn 2+ doping range ( x > 0.13). The considerably enhanced PL brightness and shorten luminescent lifetime of Zn-doped GdTaO 4 :Eu 3 is very encouraging for the display applications.