White organic light-emitting diodes based on blue fluorescent bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb)2] doped with DCM dye

Bright white organic light-emitting diodes (WOLEDs) with single active layer has been demonstrated from blue emitting zinc complex bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb)₂] doped with orange luminescent 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM) dye. White light electroluminescence (EL) spectrum from Zn(hpb)₂ has been achieved by adjusting the concentration of DCM dye. WOLED with a structure of ITO/α-NPD/Zn(hpb)₂:DCM (x%)/BCP/Alq₃/LiF/Al has been fabricated. The EL spectra covering the whole visible spectra range of 400–700 nm, with two peaks at 446 and 555 nm has been measured. The device emits white light at 10 V with Commission Internationale de I’ Eclairage (CIE) coordinates (0.27, 0.31) and brightness 1083 Cd/m². The maximum current efficiency of the device was 1.23 Cd/A at 9.5 V and maximum luminance reaches 2210 Cd/m² at 12 V.     

Psychophysical estimation of speed discrimination. I. Methodology

Thresholds were assessed for a speed discrimination task with a pair of luminance-defined drifting gratings. The design and results of a series of experiments dealing in general with speed discrimination are described. Results show that for a speed discrimination task using drifting gratings, simultaneous presentation of the pair of gratings (spatially separated) was preferred over sequential presentation (temporally separated) in order to minimize the effects of eye movements and tracking. An interstimulus interval of at least 1000 ms was necessary to prevent motion aftereffects on subsequently viewed stimuli. For the two reference speeds tested of 2 and 8 deg/s using identical spatial frequency or randomizing spatial frequency for the pair of gratings did not affect speed discrimination thresholds. Implementing a staircase method of estimating thresholds was preferred over the method of constant stimuli or the method of limits. The results of these experiments were used to define the methodology for an investigation of aging and motion perception. These results will be of interest and use to psychophysicists designing and implementing speed discrimination paradigms.     

Electrical conduction behaviour of cobalt substituted BaSnO3

A few cobalt substituted barium stannate, BaSn_1–x Co _x O₃ compositions have been synthesized by solid state ceramic method. Seebeck coefficient has been measured as a function of temperature. Positive values of '' indicate that holes are the majority charge carriers. AC conductivity, _ac has been measured in the temperature range 310–550 K and frequency range 100 Hz to 10c MHz. The contributions of the grains and grainboundaries to the total conductivity have been obtained by complex plane impedance analysis. Complex plane impedance analysis shows that conduction occurs by hopping of charge carriers among localized sites.     

International Collaboration in Science in India and its Impact on Institutional Performance

In this paper, our objective is to delineate some of the problems that could arise in using research output for performance evaluation. Research performance in terms of the Impact Factor (IF) of papers, say of scientific institutions in a country, could depend critically on coauthored papers in a situation where internationally co-authored papers are known to have significantly different (higher) impact factors as compared to purely indigenous papers. Thus, international collaboration not only serves to increase the overall output of research papers of an institution, the contribution of such papers to the average Impact Factor of the institutional output could also be disproportionately high. To quantify this effect, an index of gain in impact through foreign collaboration (GIFCOL) is defined such that it ensures comparability between institutions with differing proportions of collaborative output. A case study of major Indian institutions is undertaken, where Cluster Analysis is used to distinguish between intrinsically high performance institutions and those that gain disproportionately in terms of perceived quality of their output as a result of international collaboration. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis and electroluminescence characterization of a new aluminium complex, [8- Hydroxyquinoline] Bis [2,2’Bipyridine] Aluminium Al(Bpy)2q

We have synthesized and characterized a new electroluminescent material, [8-Hydroxyquinoline] Bis [2,2’Bipyridine] aluminium. Solution of this material Al(Bpy)₂q in toluene showed absorption maxima at 380nm which was attributed to the moderate energy (π – π*) transitions of the aromatic rings. The photoluminescence spectrum of Al(Bpy)₂q in toluene solution showed peak at 518 nm.This material shows thermal stability up to 300₀C. The structure of the device is ITO/F4-TCNQ(1nm)/α-NPD(35nm)/Al(Bpy)₂q(35nm)/ BCP(6nm)/Alq₃(28nm)/LiF(1nm)/Al(150nm). This device exhibited a luminescence peak at 515 nm (CIE coordinates, x=0.32,y=0.49). The maximum luminescence of the device was 214 Cd/m₂ at 21V. The maximum current efficiency of OLED was 0.12 Cd/A at 13V and maximum power efficiency was 0.03 lm/W at 10 volt.     

Synthesis and Electroluminescence properties of Tris [ 5-choloro- 8- hydroxyquinoline] Aluminium Al(5-Clq)3

A new electroluminescent material tris-[5-choloro-8-hydroxyquinoline] aluminum has been synthesized and characterized. Solution of this material Al(5-Clq)₃ in toluene showed absorption maxima at 385 nm which was attributed to the moderate energy (π-π^*) transitions of the aromatic rings. The photoluminescence spectrum of Al(5-Clq)₃ in toluene solution showed a peak at 522 nm. This material shows thermal stability up to 400 ℃. The structure of the device is ITO/0.4 wt%F4-TCNQ doped α-NPD (35 nm) / Al(5-Clq)₃(30 nm)/ BCP (6 nm)/ Alq₃(30 nm)/ LiF (1 nm)/Al(150 nm). This device exhibited a luminescence peak at 585 nm (CIE coordinates, x= 0.39, y= 0.50). The maximum luminescence of the device was 920 Cd/m² at 25 V. The maximum current efficiency of OLED was 0.27 Cd/A at 20 V and maximum power efficiency was 0.04 lm/W at 18 V.     

Outcoupling efficiency enhancement in organic light emitting diodes via nano-structured indium tin oxide and nano-phosphors

Nanostructures of indium tin oxide (NSITO) deposited using glancing angle deposition (GLAD) technique are used to enhance the outcoupling efficiency of blue and green OLEDs. The enhancement was found to be angle independent. The efficiency of device has increased by about 2.1 times by the use of NSITO at glass/air interface and ITO/glass interface. Similarly nano-phosphor particles were used to recover the glass modes by depositing them on the backside of the substrates. Both these methods were found to be effective for outcoupling efficiency enhancement.     

Initial-stage Sintering Kinetics of Nanocrystalline Tungsten

Initial-stage sintering kinetics of nanocrystalline tungsten has been studied in the temperature range of 1273–1473 K (1000–1200 °C). Nanocrystalline tungsten sinters initially through a grain boundary diffusion mechanism. The calculated activation energy was 388 ± 11 kJ/mol at low temperatures (1273–1373 K (1000–1100 °C)) and 409 ± 7 kJ/mol at high temperatures (1373–1473 K (1100–1200 °C)), which are close to the experimentally measured activation energy for grain boundary diffusion (385 kJ/mol).     

Acclimatization of microalgae Arthrospira platensis for treatment of heavy metals in Yamuna River

Bioaccumulation and biosorption in microalgae are effective approaches for the removal of heavy metals (HMs) from river water. The objective of this study was to investigate the potential for use of acclimatized microalgae in the removal of HMs from the Yamuna River water as an acclimatizing medium. An active culture of Arthrospira platensis (A. platensis) was acclimatized to HMs up to a concentration of 100 mg/L. It was gradually exposed to increasing concentrations of HMs in five subsequent batches with a step increase of 20 mg/L to acclimatize live cells in the simulated Yamuna River water. The presence of high levels of HMs in the Yamuna River water caused growth inhibition. An empirical growth inhibition model was developed, and it predicted high threshold concentrations of HMs (210.7–424.5 mg/L), producing a positive specific growth rate of A. platensis. A. platensis also showed high average removal efficiencies of HMs, including 74.0% for Cu, 77.0% for Cd, 50.5% for Ni, 76.0% for Cr, 76.5% for Pb, and 63.5% for Co, from HMs-enriched Yamuna River water. The findings demonstrated that the maximum specific removal amounts of Cu, Cd, Ni, Cr, Pb, and Co were 54.0, 58.0, 39.0, 62.8, 58.9, and 45.3 mg/g, respectively. The maximum yields of the value-added products chlorophyll and phycocyanin were 2.5 mg/g (in a batch of 40 mg/L for Cd) and 1 054 mg/g (in a batch of 20 mg/L for Cu), respectively. Therefore, acclimatized A. platensis was proven to be a potential microalga not only for sequestration of HMs but also for production of valuable pigments.