Excitation power and temperature dependence of excitons in CuInSe2

Excitonic recombination processes in high quality CuInSe2 single crystals have been studied by photoluminescence (PL) and reflectance spectroscopy as a function of excitation powers and temperature. Excitation power dependent measurements confirm the identification of well-resolved A and B free excitons in the PL spectra and analysis of the temperature quenching of these lines provides values for activation energies. These are found to vary from sample to sample, with values of 12.5 and 18.4meV for the A and B excitons, respectively, in the one showing the highest quality spectra. Analysis of the temperature and power dependent PL spectra from the bound excitonic lines, labelled M1, M2, and M3 appearing in multiplets points to a likely assignment of the hole involved in each case. The M1 excitons appear to involve a conduction band electron and a hole from the B valence band hole. In contrast, an A valence band hole appears to be involved for the M2 and M3 excitons. In addition, the M1 exciton multiplet seems to be due to the radiative recombination of excitons bound to shallow hydrogenic defects, whereas the excitons involved in M2 and M3 are bound to more complex defects. In contrast to the M1 exciton multiplet, the excitonic lines of M2 and M3 saturate at high excitation powers suggesting that the concentration of the defects involved is low. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709448

Excited states of the free excitons in CuInSe2 single crystals

High-quality CuInSe2 single crystals were studied using polarization resolved photoluminescence (PL) and magnetophotoluminescence (MPL). The emission lines related to the first (n=2) excited states for the A and B free excitons were observed in the PL and MPL spectra at 1.0481 meV and 1.0516 meV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 meV and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (E-g(A)=1.050 eV and E-g(B)=1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model

Diamagnetic shift of the A free exciton in CuGaSe2 single crystals

Single crystals of CuGaSe2 were studied using magnetophotoluminescence inmagnetic fields up to 20 T at 4.2 K. The rate of the diamagnetic shift in the A free exciton peak was determined to be 9.82 x 10(-6) eV/T-2. This rate was used to calculate the reduced mass as 0.115m(0), the binding energy as 12.9 meV, the Bohr radius as 5.1 nm and an effective hole mass of 0.64m(0) (m(0) is the free electron mass) of the free A exciton using a low-field perturbation approach and the hydrogenic model

Non-market Valuation Biases Due to Aboriginal Cultural Characteristics in Northern Saskatchewan: The Values Structures Component

Current non-market valuation techniques have been developed based on assumptions about values held within the Eurocentred culture. Contentions between cultures over natural resources are hypothesized to occur because of differences in held values resulting in different values being assigned to the resources in question. This study measured the held values of an Aboriginal band in Northern Saskatchewan as the first dimension of a non-market valuation study of natural resources. These held value structures are presented noting differences by age and gender and in comparison with the local Non-Aboriginal community and another Aboriginal group in northern Alberta.Resource /Energy Economics and Policy,

Optical properties of high quality Cu2ZnSnSe4 thin films

Cu2ZnSnSe4 thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu2ZnSnSe4 thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectr

In search of optimal stocking regimes in semi-arid grazing lands : one size does not fit all

We discuss the search for optimal stocking regimes in semi-arid grazing lands. We argue that ‘one size does not fit all’ and that different stocking regimes are appropriate under different conditions. This paper is an attempt to move beyond polarization of the current debate towards a more integrative and flexible approach to grazing management. We propose five different conditions as major influences on grazing regimes: environmental variability and predictability; degradation and thresholds; property right regimes; discount rates; and market stability and prices. We suggest a lack of connection between the micro-economics literature and natural science and social-anthropological literature. It is timely to achieve greater integration around some key questions and hypotheses, and recognize that policy prescriptions at national or even regional levels are likely to have limited value due to context specificity

Forest certification: economic issues and welfare implications

Working Paper SES-

Buddy taping after reduction of displaced extra-articular phalangeal finger fractures in children: a randomized controlled trial

In this randomized controlled trial, we assessed the non-inferiority of buddy taping to splinting after reduction of displaced extra-articular proximal and middle phalangeal finger fractures in children. The primary outcome was the rate of secondary fracture displacements; the secondary outcomes were patient comfort, analgesic efficacy and total range of active motion 6 months after injury. Eighty-one patients participated: 43 with taping and 38 with splinting. Secondary displacement occurred in eight patients: five in the splinting group and three in the taping group. Risk difference was below the predefined non-inferiority of 10%. Patient comfort was significantly higher in the taping group, with no group differences for other parameters. Our previous study recommended taping for undisplaced finger fractures in children. With the current data, we recommend taping these finger fractures irrespective of displacement or need for reduction. We are encouraged to propose taping as an alternative to splinting for increased patient comfort, lower cost, and shorter application time. Level of evidence:

Maize and upland rice traits of importance for farmers practicing manual rainfed agriculture in the humid tropics : a Panamanian case-study

The agronomic practices and concerns of poor farmers in comparable ecozones are often similar across countries and regions. Crop ideotypes have helped guide selection for yield under high fertility monoculture conditions in formal breeding programs and could be used to direct breeding for the agricultural conditions of poor farmers. However, the objectives and selection criteria of poor farmers may differ from those of formal breeding programs. This study illustrates a simple survey method for detecting crop traits that are important to poor farmers, and describes results for upland rice and maize ideotypes cropped by swidden agriculturalists in Panama. Our results suggest that formal breeding programs are working on individual crop traits that are important to poor farmers, but they may not be developing varieties that incorporate multiple individual traits (ideotypes), which farmers desire. National breeding programs should play crucial roles in identifying and breeding for regional ideotypes that vary with farming practices and cultural preferences. The field survey techniques reported herein are reproducible, quickly orient breeders towards crop traits that are potentially important to farmers, provide information on the processes underpinning trait importance, and capitalize on decades of farmer experience