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 diamond’s 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

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>_g 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:PC₇₁BM 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