6 research outputs found
Can Europium Atoms form Luminescent Centres in Diamond: A combined Theoretical-Experimental Study
The incorporation of Eu into the diamond lattice is investigated in a
combined theoretical-experimental study. The large size of the Eu ion induces a
strain on the host lattice, which is minimal for the Eu-vacancy complex. The
oxidation state of Eu is calculated to be 3+ for all defect models considered.
In contrast, the total charge of the defect-complexes is shown to be negative
-1.5 to -2.3 electron. Hybrid-functional electronic-band-structures show the
luminescence of the Eu defect to be strongly dependent on the local defect
geometry. The 4-coordinated Eu substitutional dopant is the most promising
candidate to present the typical Eu3+ luminescence, while the 6-coordinated
Eu-vacancy complex is expected not to present any luminescent behaviour.
Preliminary experimental results on the treatment of diamond films with
Eu-containing precursor indicate the possible incorporation of Eu into diamond
films treated by drop-casting. Changes in the PL spectrum, with the main
luminescent peak shifting from approximately 614 nm to 611 nm after the growth
plasma exposure, and the appearance of a shoulder peak at 625 nm indicate the
potential incorporation. Drop-casting treatment with an electronegative polymer
material was shown not to be necessary to observe the Eu signature following
the plasma exposure, and increased the background luminescence.Comment: 12 pages, 7 figures, 5 table
Taxon-independent and taxon-dependent responses to drought in seedlings from Quercus robur L., Q. petraea (Matt.) Liebl. and their morphological intermediates
The increasing severity and frequency of summer droughts at mid-latitudes in Europe may impact forest regeneration. We investigated whether the sympatric species Quercus robur L., Q. petraea (Matt.) Liebl., and their morphological intermediates respond differentially to water deficit. Acorns were sourced from a naturally mixed population. Half of the potted seedlings were subjected to two successive drought periods during the first growing season, each followed by a plentiful re-watering. The surviving drought-exposed seedlings subsisted independent of the taxon of the mother tree. The phenological responses were also taxon-independent. However, drought-exposed plants showed a retarded height growth in the year following the treatment which was taxon-dependent. Offspring from Q. robur and from trees with leaves resembling Q. robur leaves and infructescences resembling Q. petraea infructescences showed a stronger decrease in height growth compared to the offspring from Q. petraea and from trees with leaves resembling Q. petraea leaves and infructescences resembling Q. robur infructescences. Diameter growth in the year following the drought treatment showed a weak taxon-dependent response. Together, our results may suggest that the composition of oak species and their hybrids in natural oak forests could be altered upon prolonged periods of precipitation deficit
Taxon-Independent and Taxon-Dependent Responses to Drought in Seedlings from Quercus robur L., Q. petraea (Matt.) Liebl. and Their Morphological Intermediates
The increasing severity and frequency of summer droughts at mid-latitudes in Europe may impact forest regeneration. We investigated whether the sympatric species Quercus robur L., Q. petraea (Matt.) Liebl., and their morphological intermediates respond differentially to water deficit. Acorns were sourced from a naturally mixed population. Half of the potted seedlings were subjected to two successive drought periods during the first growing season, each followed by a plentiful re-watering. The surviving drought-exposed seedlings subsisted independent of the taxon of the mother tree. The phenological responses were also taxon-independent. However, drought-exposed plants showed a retarded height growth in the year following the treatment which was taxon-dependent. Offspring from Q. robur and from trees with leaves resembling Q. robur leaves and infructescences resembling Q. petraea infructescences showed a stronger decrease in height growth compared to the offspring from Q. petraea and from trees with leaves resembling Q. petraea leaves and infructescences resembling Q. robur infructescences. Diameter growth in the year following the drought treatment showed a weak taxon-dependent response. Together, our results may suggest that the composition of oak species and their hybrids in natural oak forests could be altered upon prolonged periods of precipitation deficit.status: publishe
Expanding the Scope of Diamond Surface Chemistry: Stille and Sonogashira Cross-Coupling Reactions
Well-defined covalent
surface functionalization of diamond is a
crucial, yet nontrivial, matter because of diamondâs intrinsic
chemical inertness and stability. Herein, we demonstrate a two-step
functionalization approach for H-terminated boron-doped diamond thin
films, which can lead to significant advances in the field of diamond
hybrid photovoltaics. Primary diamond surface functionalization is
performed via electrochemical diazonium grafting of <i>in situ</i> diazotized 4-iodoaniline. The freshly grafted iodophenyl functional
moieties are then employed to couple a layer of thiophene molecules
to the diamond surface via two well-established Pd-catalyzed cross-coupling
reactions, i.e., Stille and Sonogashira. X-ray photoelectron spectroscopy
analysis indicates a dense coverage and successful cross-coupling
in both cases. However, we find that the Stille reaction is generally
accompanied by severe surface contamination, in spite of process optimization
and thorough rinsing. Sonogashira cross-coupling on the other hand
provides a clean, high quality functionalization over a broad range
of reaction conditions. The protocols employing Sonogashira reactions
thus appear to be the method of choice toward future fabrication of
high-performance dye-functionalized diamond electrodes for photovoltaic
applications
Taxon-Independent and Taxon-Dependent Responses to Drought in Seedlings from Quercus robur L., Q. petraea (Matt.) Liebl. and Their Morphological Intermediates
Enhanced Organic Solar Cell Stability by Polymer (PCPDTBT) Side Chain Functionalization
Organic
photovoltaics represent a promising thin-film solar cell technology
with appealing mechanical, aesthetical, and cost features. In recent
years, a strong growth in power conversion efficiency (to over 10%)
has been realized for organic solar cells through extensive material
and device research. To be competitive in the renewable energy market,
further improvements are mandatory though, both with respect to efficiency
and lifetime. High intrinsic stability of the photoactive layer is
obviously a crucial requirement for long lifetimes, but the generally
applied bulk heterojunction blends and their components are prone
to light-induced and thermal degradation processes. In the present
contribution, the high-<i>T</i><sub>g</sub> polymer strategy
is combined with specific side chain functionalization to address
the thermal stability of polymer solar cells. These two design concepts
are applied to a prototype low bandgap copolymer, PCPDTBT. Accelerated
aging tests (at 85 °C) indicate an improved thermal durability
of the PCPDTBT:PC<sub>71</sub>BM blends and the resulting devices
by the insertion of ester or alcohol moieties on the polymer side
chains. The different stages in the efficiency decay profiles are
addressed by dedicated experiments to elucidate the (simultaneously
occurring) degradation mechanisms