In many areas of developing countries, agriculture soil is irrigated with water from drains contaminated with industrial wastewater that contains many toxic substances including arsenic. Such sites could be explored for arsenic-resistant plant growth-promoting microbes. Ten arsenic-resistant bacteria were isolated from such a site and were characterized. Their ability to resist and reduce/oxidize arsenic was determined. The bacteria were also analyzed for plant growth-promoting abilities such as auxin and hydrogen cyanide production, phosphate solubilization, and nitrogen fixation. The effect of these bacteria on plant growth was determined using Vigna radiata both in presence and absence of arsenic. Bacterial isolates S254 and S255 showed maximum resistance against arsenic; up to 225 mM of As(V) and 25 mM of As(III). The phylogenetic analysis revealed that strain S254 belonged to the species Pseudoxanthomonas mexicana and strain S255 belonged to the species Stenotrophomonas maltophilia. Both P. mexicana S254 and S. maltophilia S255 showed positive results for hydrogen cyanide production, auxin production, and nitrogen fixation. P. mexicana S254 produced auxin at a concentration of 14.15 µg mL−1 and S. maltophilia S255 produced auxin as high as 68.75 µg mL−1. Both the bacteria-enhanced the growth of V. radiata and a statistically significant increase in shoot and root lengths was observed both in the presence and absence of arsenic. The application of such bacteria could be helpful for the growth of plants in arsenic-contaminated lands.
Chromium doped aluminum nitride (AlN: Cr) thin films were grown on silicon, glass and copper substrates by DC and RF magnetron sputtering co-deposition. After growth, thin films on silicon substrates were annealed at 1373 K for 30 min in N2 atmosphere. The AlN: Cr thin films were characterized by x-ray diffraction for structural analysis, by FS5 spectrofluorometer for the study of photoluminescence, absorption, transmission, and chromaticity. As-deposited and annealed silicon substrate and as-deposited glass substrate thin films of AlN: Cr exhibited intense photoluminescence emission in the range of 400 to 679.5 nm. Spectral evidence demonstrated conclusively that the AlN: Cr thin films on as-deposited glass substrate and annealed silicon substrate have excellent photoluminescence emission which is due to both AlN (host) and Cr3+ ions. The reasons of photoluminescence of AlN in the visible region are surface defects and impurities. Impurities become the cause to produce different types of defects and vacancies just like oxygen point defects (O+N), nitrogen vacancies (VN) and various defect complexes (V3-Al – 3 O+N). It may also be due to the recombination of photogenerated hole with the electron occupied by the nitrogen vacancies and due to the transition between deep level of (V3-Al – 3 O+N) defect complexes and shallow level of VN and the reason behind the photoluminescence of Cr3+ ions is due to vibrational energy levels 4T1 and 4T2 and due to 4T1→4A2 and 4T2→4A2 transitions. AlN: Cr thin films can give better results in the applications like light emitting diodes (LEDs), laser diodes (LDs), field emission displays, microelectromechanical system (MEMS), optical MEMS and biomedical applications. Key words: III-V Semiconductor Material, Thin films, Photoluminescence Mechanism
Well dispersed Aluminum Nitride (AlN) nanopowder and AlN thin film were compared to observe their structural and luminescence properties. AlN thin films were deposited on silicon and copper substrates by RF magnetron sputtering. PL peaks analysis indicated the same pattern of emission peaks over different excitation wavelengths ranging from 200 nm to 300 nm for both the AlN nanopowder and thin film, nearly 100 -1000 times PL increment observed in AlN nanopowder. It is suggested that the reason for PL of AlN material is due to surface defects and impurities like oxygen-related point defects (O+N), nitrogen vacancies (VN), the transition from the donor level of VN (nitrogen-vacancy) to the acceptor level of AlN (antisites defects), and various defect complexes (V3-Al – 3 O+N) are responsible for the enhanced observed emission peaks. With well-defined emission curves, AlN Nanopowder and thin films are observed to be good substrate and insulator material for microelectronic circuits, Light Emitting Diodes, Laser Diodes, and in biomedical applications such as bioimaging and biosensors.
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