In this work, we have synthesized high quality TiO2 nanocrystallites by sol–gel method (TiO2 white (w)) and compared its properties with the ones synthesized by the simple hydrolysis method in aqueous solution (TiO2 transparent (t)). The TiO2/MEH-PPV nanocomposites are formed mainly by two ways: (i) Prepared in the form of the colloidal solution by adding the known concentration of the TiO2 in MEH-PPV and then sonicate it well; (ii) In the thin film form by depositing the above solution over a glass substrate by spin coating. The properties of the resulting dispersions could be tailored by varying the composition and concentration of TiO2 nanoparticles in CP's. The TiO2 nanoparticles prepared by both methods show anatase character of TiO2 as elucidated by X-ray diffraction (XRD) studies. Transmission electron microscopic (TEM) studies reveal that the transparent colloidal suspension of TiO2 exhibits agglomeration of TiO2 nanoparticles (size~150–300nm) and this trend is maintained in the MEH-PPV matrix for TiO2/MEH-PPV composites as well. However, the composite obtained by mixing MEH-PPV with sol–gel prepared TiO2(w) shows uniform nanoscale dispersion of TiO2 (size~20nm) in MEH-PPV matrix. The UV–VIS absorption, photoluminescence (PL) and lifetime studies confirm the presence of dynamic quenching effect indicating efficient photoinduced charge transfer in TiO2/MEH-PPV hybrid composites particularly with white TiO2. It is conjectured that the devices containing TiO2/MEH-PPV composites for TiO2 prepared by the sol–gel method should lead to significant improvement in the photovoltaic performance of TiO2/MEH-PPV hybrid solar cells.

A diethanolamine stabilized precursor sol has been utilized for studying the effect of sol aging and annealing temperature on key properties of TiO 2 films. X-ray diffraction investigations have shown increased crystallite size in the films as a function of both sol aging and the thermal treatment. Fourier transform infrared studies have elucidated that cleavage of the bond involving diethanolamine and the alkoxide in the films requires high temperature annealing treatment upon the use of aged sol for the deposition of the films. Multiple step chronoamperometry has shown the ion storage capacity of the films increases as a function of sol aging, with the highest extent of Li ion insertion being obtained for films produced from as-prepared and aged sols and subsequently annealed at, 300 and 350 °C, respectively. Films with excellent optical quality were obtained. Ellipsometry revealed that the refractive indices of the films vary from 1.67 to 2.02. The highest thickness obtained in these films was nearly 900 nm. The bandgaps of the films for both direct and indirect transitions decreased as a function of precursor sol’s aging. In addition, although the indirect bandgap values have shown a decrease with increasing annealing temperature, the direct bandgap values reveal a slight increase as a function of annealing temperature.

We report a simple approach to prepare cost effective antireflective surface directly on silicon wafers, which consists of arrays of vertically aligned silicon nanowires (VA-SiNWA). Large area VA-SiNWA were realized by silver induced wet chemical etching of p-silicon (100) substrates in aqueous HF and AgNO3 solution at room temperature. Length of Si wires (diameter in 50–300nm range) was found to increase linearly with etching time (0–120min). A remarkable reduction in reflectivity (Rλ) for surfaces with Si wires was observed. The value of Rλ less than 2% was realized in the 300–600nm wavelength range in the case of ∼12μm long Si wires, a value better than the best Rλ reported in anisotropically textured surface or single layer antireflection coatings. The VA-SiNWA behaves as a subwavelength structured surface that could suppress the reflectivity to a great extent. Such surfaces may have potential applications as antireflection surface for silicon solar cells.

Sodium phosphate glass systems with AgCl as dopant (0 and 15mol%) have been synthesized by melt-quenching technique. The glasses in bulk form were characterized by X-ray diffraction, FT-IR spectroscopy and their thermal and electrical properties were investigated. These glasses were deposited on glass substrates by thermal evaporation method in thin film form and annealed at 600°C. The influence of deposition in thin film form and annealing on structure and optical properties (transmittance, absorbance and optical gap) have showed that both doped and undoped as-deposited glass films have a porous, granular structure and considerable grain coarsening and densification occur upon annealing at 600°C. The optical transmittance of the film is found to decrease in visible region as a function of annealing and doping. The annealed 15mol% doped film shows a prominent absorbance peak at 430nm, which is ascribed to Ag+(5s)←O(n) electronic transitions.

Sol–gel grown polycrystalline Al doped zinc oxide (AZO) thin films have been deposited on Si wafers, microscopy slide glass and fluorine doped tin oxide coated glass substrates using the spin coating technique. The atomic ratio of Al:Zn in the films is 0.2. From the X-ray diffraction investigations it is found that the preferential growth of (100) reflection peak has taken place in the 450, 550 and 600°C annealed films. Scanning electron microscopic study has shown that the films contain well-defined grains arranged in a closely packed array. The resistivity of the 500°C annealed film is measured to be 5×10−1Ωcm. The films have exhibited excellent optical transmittance (~90%) in the 400–1100nm wavelength range. Refractive indices (n=1.9–1.95) of the films on Si wafer are independent of the annealing temperature. Thickness of the films produced at 4000rpm is in the range of 58–62nm. The refractive index and thickness of these films are nearly appropriate to cause destructive interference after reflection from front emitters of solar cells. These films have demonstrated a reflectivity value of about 3% at a wavelength of 700nm. The AZO coated silicon solar cells possess Voc and Isc values of 573mV and 237mA, respectively.

(50-x)Na2O-50P2O5-xAgCl (x = 0 to 15 mol%) glasses in bulk form were synthesized using melt-quenching technique. Thin films of these silver doped sodium phosphate glasses were deposited by thermal evaporation process. The influence of deposition of these glasses in thin film form and subsequent annealing at 600 degrees C on the structure and optical properties such as transmittance, reflectance, refractive index and band gap have been investigated in detail. X-ray diffraction studies of the as-deposited films show the films to be amorphous whereas annealed films show existence of orthorhombic and monoclinic phase of NaPO3 along with crystalline cubic phase of AgCl in doped glasses. Structural investigations of these annealed films show unique morphologies (needle-like and granular) at nano-scale. Both as-fabricated and annealed films are poor reflectors but show high transmittance in the entire spectral region under consideration, which is a direct consequence of particle size effects. Indirect band gap narrowing and variation in refractive index upon annealing is consistent with nanostructural transformations in these samples.

In this work, it has been demonstrated that the co-ordinating tri-n-octylphosphine and oleic acid mixture plays an essential role in the control of the growth, size distribution, colloidal stability, crystallinity and shape of the resulting PbSe nanocrystals. A systematic combination of the reaction and growth conditions allows the possibility to produce high quality PbSe nanocrystals over a broad range of diameters with narrow size distributions without any size selective precipitation techniques being applied. The capping agent/ligands helps to control the grain growth of the nanocrystals during its formation and increases the dispersibility of the nanocrystals, which can easily be manipulated and used for various applications in optoelectronics and microscopy.

Electrochemical synthesis of tungsten oxide (WO3) thin film nanostructures by potentiostatically controlling the surface aggregates formed at the electrode–electrolyte interface, in the presence of a polymeric template (polyethylene glycol 400, PEG) from a plating sol of peroxotungstic acid (PTA) is presented. The nanoparticulate morphology of the WO3 film changes drastically upon varying PEG content in the precursor sol; from an amorphous structure with randomly distributed pores for a film derived from a PTA sol with PEG:ethanol in a 3:7 volume ratio, to a mesoporous, nanocrystalline material with hybrid structures encompassing spherical grains and nanorod-like shapes with a triclinic modification for a film formed in a sol with PEG:ethanol in a 1:1 volume ratio. This approach highlights the role of the PEG proportion in controlling crystal growth, assembly patterns and pore structure. The film derived from the sol with PEG:ethanol in a 1:1 volume ratio exhibits superior transmission modulation and coloration efficiency as compared to the film obtained from a sol with PEG:ethanol in a 3:7 volume ratio. While the latter film deteriorates rapidly within 35 color-bleach cycles, the former film sustains more than 3500 cycles, without significant degradation. This film also exhibits fast switching between the clear and blue states; these are repercussions of the mesopore structure and the interconnected nanocrystallite phase.

Diethanolamine derived clear precursor sol has been utilized for the deposition of TiO2 films annealed at 470°C for 5min. Effect of the precursor sol's aging on different properties of the films has been examined in the present study. Films obtained from aged sol have exhibited superior electrochemical (diffusion coefficient—2.46×10−10cm2s−1) and electrochromic characteristics due to enhanced Li ion insertion upon application of electric field. The aged sol derived films have exhibited a higher optical modulation (40% at 550nm) between the colored and bleached states. The ion storage capacities of the films derived from freshly prepared and aged sols are 4.1 and 8.1mCcm−2, respectively, upon applied voltage of ±1.5V. X-ray diffraction studies have affirmed an increase in the TiO2 crystallite size upon the use of aged sol for the deposition of films. FTIR investigations have confirmed the conversion of Ti–O–Ti to Ti–O network in the aged sol derived films. SEM studies have evidenced porosity changes in films obtained from the sol aged for different durations. The index of refraction as measured by the ellipsometry method corroborates the SEM results and shows reduced porosity (pore size—38nm) in films derived from the sol just reaching the state of gelation. Thickness of the aged sol derived film is measured to be the highest i.e. 350nm. Energy bandgaps of the films for both direct and indirect transitions tend to decrease as a function of sol's aging.

ZnO and its ternary alloy ZnMgO offer an excellent material system with potential in applications related to quantum well and photonic devices in UV and visible. ZnO and ZnO/MgO composite were prepared by solid-state mixing and sintering at high temperature in reducing atmosphere. ZnO/MgO nanocomposites up to 50% Mg content could be prepared by this method. The resultant sample was in powder form and has distribution of grain sizes. X-ray diffraction showed hexagonal ZnO structure with small signature of cubic MgO, which increased with increasing Mg content. Particle size estimated from Scherrer formula was in the range of 40nm, which reflected the average crystallite size. Photoluminescence (PL) studies showed excitation peak around 290nm (4.3eV) and 350nm (3.5eV). Pure ZnO nanophosphor showed emission peak around 508nm, which blue shifted with increasing Mg content. Time resolved decay of PL indicated decay time in the microsecond time scale. Optical absorption spectra showed bandgap about 5.6eV for ZnO/MgO nanocomposite with 50% Mg content. The optical absorption measurement was done in the colloidal suspension form and it is expected that only nanoparticles of very small grain size were effectively contributing to the optical absorption process. The large bandgap could then be manifestation of quantum size effect.

Sol–gel derived, as-deposited amorphous tungsten oxide (WO3) films become nanocrystalline with a pseudocubic triclinic structure upon annealing at 600 °C. The annealed films are constituted of nanorods along with interconnected nanoparticles and pores. While the high transmission modulation and colouration efficiency in the visible region and the fast bleaching kinetics as shown by the nanostructured film were typical of amorphous WO3, the absorption coefficient spread in the 300–2000 nm wavelength range, the reflectance modulation and the colouration efficiency peak in the NIR region were reminiscent of crystalline WO3. The larger magnitude of the indirect band gap shift to blue than the direct gap shift for the same level of lithium intercalation (18 mC cm−2) and the irreversibility of the direct gap shift upon bleaching are characteristic of the nanocrystalline structure of the film. The moderate decline in the anodic peak current maximum, the diffusion coefficient for lithium and the optical modulation at 632.8 nm upon repetitive switching between the coloured and bleached states ratified that nanostructured films sustain 1000 cycles without much deterioration.

Hitherto unexplored irreversible changes during initial coloration/bleaching cycles for sol–gel-derived tungsten oxide (WO3) films have been investigated using cyclic voltammetric and spectrophotometric techniques. Non-ideal features appearing in the initial five anodic (deintercalation) cycles in the voltammogram with simultaneous decreased optical transmission of the bleached films have been explained in terms of possible stoichiometric variations affecting the coloration efficiency (CE) of the films and the associated mechanisms. Electrochromic stability attained thereafter manifests in retraceable voltammograms and almost invariant value of the CE.

The development of nanophosphors of desired sizes and properties for various practical applications and its growth in quantitative amounts inside the pores of an inorganic matrix is presented. By doing so, nanophosphors get surface passivated and are stabilized against environmental attacks. Accordingly, in the present study, the growth parameters for ZnS:Mn nanophosphors were systematically studied inside a SiO2 gel matrix, which can act as a capping agent as well. The samples were prepared using the sol-gel technique, followed by annealing at different temperatures to remove the trapped fluid inside the amorphous silica cage. Two categories of samples with lower (3.11×10−4) and higher (1.5×10−1) ZnS∕SiO2 molar ratios were studied. The x-ray diffraction and scanning electron microscopy observations show that upon annealing, the nanocrystals grow in size and undergo a phase transition from cubic to hexagonal at temperatures between 700 and 900°C. This is one of the very few known reports published on nano hexagonal ZnS formation. The observed phase transition is possibly the combined effect of the high-temperature (∼900°C) and annealing-related compressive stress induced on the nano-ZnS by the silica cage. There has been formation of an intermediate metastable phase of the zinc silicate at annealing temperatures around 700°C. The particle size distribution and emission properties were correlated using the optical absorption and photoluminescence (PL) results. The unannealed cubic nano-ZnS:Mn samples gave a broad PL, peaking at ∼585nm, whereas the samples annealed at 900°C for 5h gave a narrow and sharp PL at ∼590nm. This is attributed to the more efficient T14→A16 transitions of Mn in the resultant hexagonal nano-ZnS matrix.

Thin films of mixed CeO2-TiO2 with different Ce/Ti mole ratios were prepared following an alcohol based sol-gel route via the spin coating technique using mixed inorganic-organic [CeCl3.7H2O and Ti(OPr)4] precursors. Ion storage capacity for films obtained from aged sols was observed to be high. Enhanced titanium oxide content improved the insertion capacity of the corresponding films as was evident from inserted charge determined by multiple step chronoamperometric measurements. Electrochemical, optical, structural and thermal performances showed the suitability of the films in an all solid state electrochromic (transmissive) device with tungsten trioxide (WO3) as electrochromic material and a conductive polymeric electrolyte based on lithium.

A potentiostatic electrochemical procedure employing an ethanolic solution of peroxotungstic acid yielded tungsten oxide (WO3) films specifically for transmissive electrochromic devices (ECDs) such as “smart windows”. The structure–property correlation for the as-deposited thin films of WO3 and the films annealed at different temperatures (60, 100, 250 and 500 °C) is described. While the as-deposited film comprises of a small volume fraction of nanocrystals, the films annealed at 60 and 100 °C are X-ray amorphous, the 250 °C film is triclinic and the 500 °C film is characterized by mixed triclinic and hexagonal crystalline phases. Scanning electron micrographs (SEMs) clearly reveal the presence of nanograins/crystallite aggregates in the heat-treated films. Coloration renders the 250 °C film amorphous and reduces the crystallite size in the as-deposited and 500 °C films. Thermal analysis provides information pertaining to the critical temperatures at which dehydration, peroxo group decomposition and crystallization occur. Fourier transform infrared (FTIR) spectroscopic data show that while the as-deposited WO3 film is composed of a peroxopolytungstate ion network with water molecules acting as bridging groups, the crystalline film annealed at 500 °C shows absorption bands characteristic of the W–O–W network (polytungstate ions linked through oxygens). Coloration efficiency (CE; η) and transmission modulation (ΔT) are slightly higher for the amorphous 60 °C film when compared with the nanocrystalline as-deposited film in the 450<λ<850 nm range, and these properties deteriorate at temperatures ≥100 °C. However, switching times between the colored and bleached states and ion storage capacities show a systematic and significant decrease with increasing annealing temperature. High transmission modulation (67.5% at 632.8 nm), fast bleaching kinetics (∼5 s), high ion storage capacity (22 mC cm−2) and a coloration efficiency of 60.5 cm2 C−1 at 632.8 nm observed for the as-deposited film render it to be a suitable candidate for electrochromic window applications. An operational lifetime of more than 104 cycles has been tested successfully for the as-deposited film against a platinum sheet as an auxiliary electrode.

Wheat (Triticum aestivum cv. Sonalika) plants were grown with three different concentrations of salicylic acid (SA; 50/500/1000 muM) for 7 days and the effects on the level of thylakoid photochemical activities were examined. SA treatment stimulated photosystem II-catalyzed electron flow in all concentrations tested. Photosystem I-associated electron transport activity was stimulated at low concentrations of SA (50 muM) but at higher concentrations (500 and 1000 muM) the electron transport activity was drastically attenuated. Thylakoids isolated from the leaves of seedlings grown with high concentrations of SA (500 and 1000 muM) showed a substantial reduction in uncoupler (NH4Cl)-mediated stimulation in electron flow. In addition, they failed to support ADP-depenclent stimulation of electron transport activity and induced a significant reduction in ATPase activity. Incubation of isolated thylakoids with SA, however, had no effect on thylakoid photofunction, indicating no direct effect of SA on photoelectron transport activity. Furthermore, high concentrations of SA specifically reduce the thylakoid cytochrome f(554) level. The results suggest that SA, depending on its concentration, imparts differential effects on the photofunction of thylakoids. A low concentration of SA favours photosynthetic activity while the high concentration induces drastic attenuation of photosynthetic activity because of the decline in cytochrome f(554).

Cotyledons of gourd (Cucurbita maxima Duchesne) and bean (Phaseolus vulgaris L.) were used to study the changes in the activities of catalase, peroxidase, acid inorganic pyrophosphatase and alkaline inorganic pyrophosphatase during ageing and the diversion in such changes that occur when cotyledon senescence was retarded by detopping the seedlings above the cotyledons. Catalase, acid inorganic pyrophosphatase and alkaline inorganic pyrophosphatase activities declined during the senescence of the cotyledons. When cotyledon senescence was retarded by detopping as marked by the increase in the levels of chlorophyll and protein, there was also an increase in the activities of these enzymes. Peroxidase activity, on the other hand, increased during the senescence of the cotyledons and detopping the seedlings resulted in a further increase in the peroxidase activity. It can be suggested that some root factor(s) probably cytokinin(s) is (are) mobilised into the cotyledons of the detopped seedlings which otherwise would have been mobilised into the shoot apices, and help retard or even reverse the senescence of the cotyledons.

Changes in the inorganic pyrophosphatase (EC 3.6.1.1) activity and the chlorophyll and α-amino nitrogen levels were studied in excised leaves of rice (Oryza sativa L. cv. Ratna) subjected to various degrees of water stress. Chlorophyll level decreased and a-amino nitrogen level increased in the turgid leaves floating on water; these changes were accelerated when the leaves were subjected to water stress (Figs. 2, 3). The decrease with time in the activity of alkaline inorganic pyrophosphatase and the increase with time in the activity of acid inorganic pyrophosphatase in water-floated turgid leaves were accelerated following water stress (Figs. 4, 5). There was an accelerated decline in the ratios of alkaline to acid inorganic pyrophosphatase activity in stressed compared to turgid leaves (Fig. 6). It was concluded that water stress enhances the senescence of excised rice leaves and that the changes in the activities of alkaline and acid inorganic pyrophosphatases can be taken as indicators of water stress in rice leaves.

AbstractExcised rice (Oryza sativa L. cv. Ratna) leaves were used to compare the changes in the levels of various biochemical intermediates and enzyme activities during senescence in turgid and water‐stressed conditions. Chlorophyll, total protein and soluble protein content decreased but α‐amino nitrogen content increased during the senescence of turgid leaves. In the leaves subjected to water stress, these changes were accelerated, the acceleration being greater with higher degree of water stress. Starch, soluble sugars, total carbohydrates and non‐reducing sugar content decreased during senescence of turgid leaves. Water stress accelerated the changes in the levels of starch and non‐reducing sugar, but the changes in the levels of soluble sugars and total carbohydrates were retarded. Reducing sugar content increased at first and then decreased in the turgid leaves, and water stress accelerated the change. The decline in the catalase activity and the increase in the peroxidase activity with time was faster in the water‐stressed leaves than in the turgid leaves. Acid inorganic pyrophosphatase activity increased, but alkaline inorganic pyrophosphatase activity decreased during the senescence of turgid leaves, and such changes were accelerated by water stress. The results suggest that water stress does not accelerate all the processes connected with leaf senescence.