R. K. Shukla

Blueshift in optical band gap in nanocrystalline Zn1−xCaxO films deposited by sol-gel method

A blueshift in the optical band gap of nanocrystalline Zn1−xCaxO thin films has been obtained. A 12.72% enhancement in the band gap of ZnO thin films has been obtained using Ca dopant for the first time. The band gap widens from 3.38 to 3.81 eV as the Ca concentration increases from x=0 to x=0.15. The films are deposited by sol-gel method and have a hexagonal wurtzite phase with no indication of calcium. Grain size lies in the range of 12–92 nm. Atomic force micrographs indicate much smaller rms surface roughness showing significantly smooth surfaces.

Optical sensor for determining adulteration in a liquid sample

An optical sensor for determining the proportional composition of two liquids in a mixture is developed. It is based on observing changes in the reflected light intensity at the glass-mixture interface brought about by the changes in the proportion of one liquid over that of the other in the mixture. Sample mixtures for this investigation here have been prepared by changing the concentration of substances such as kerosene and diesel fuel in a fixed volume of petrol. A procedure for identifying as well as evaluating the concentration of kerosene or of diesel fuel or of a mixture of the two in a sample of petrol has been reported. Evaporation of these sample mixtures is carried out by exposing them to a constant flow of air at the same temperature as that of the sample mixtures. Experimental determination of the changes in the reflected intensity are carried out by using an arrangement in which one of the two isosceles surfaces of a right-angled isosceles prism is interfaced with the sample mixture. Experimentally determined values for some of these changes are compared with the theoretical estimates for them obtained from Fresnels equation.

Effect of toxic gases on humidity sensing property of nanocrystalline ZnO film

Humidity sensing property of nanocrystalline ZnO film has been investigated over a range of 5–90RH%. Contrary to more popular electrical approach, a novel optoelectronic sensing method has been used. Performance of the humidity sensor is affected by the presence of toxic gases in atmosphere. To gauge this effect, the humidity sensing properties of the film are studied by exposing it to the environment of H2S, SO2, and CH3OH one by one. The zinc oxide film is deposited using print and fire technology. X-ray diffraction of the film shows polycrystalline structure with average grain size of 33.5nm. The effect of toxic gases on the humidity sensing behavior of the film is explained while studying surface morphology of the film. The least detectable change (LDC) in humidity is evaluated for each case. For unexposed film it is found to be 0.14RH%. The LDC in the case of SO2-exposed film is recovered back almost completely by heat treatment.

EPR studies of some thick film ferrates, aluminates and their correlation with humidity sensitivity

Abstract Ceramic types of humidity sensors using aluminates and ferrates have attracted attention of workers as stable sensors. It is expected that there are some active centers on the surface of the sensors which are responsible to break the water vapor molecule in to H3O+ and OH− ions. These active centers can be unpaired spins or dangling bonds which can be measured using electron paramagnetic resonance (EPR). In the present paper, the dangling bond density of various samples of magnesium aluminates, magnesium ferrates and their mixtures prepared at different temperatures is monitored and correlated with the sensitivity of the humidity sensor prepared. It is found that the sensitivity is increasing as the dangling bond density increases.

New approach to the measurement of refractive index

A new approach for the measurement of a refractive index is presented, following the introduction of a novel feature based on the selection of a large number of angles of incidence along a direction of symmetry at the prism-ambient interface, without moving the incident beam. This gives rise to very high sensitivities over a refractive index range determined by the divergence of this beam.

Optoelectronic refractometer characterized by high sensitivity over a wide range of refractive index

A new design for a prism-based optoelectronic refractometer proposed earlier has been investigated. Experimental results are found to be in close agreement with theoretical calculations. For a given refractive index of the prism material, the divergence of the incident conical beam and angles of the prism determine the range of refractive index of the ambient over which the refractometer remains highly sensitive. Incident conical beams of higher divergences are found to enlarge this range. This refractometer is more robust and user-friendly than other such refractometers reported in the literature. Such a device can be useful for on-line measurements of refractive indices in process control systems.

Sol–Gel Derived Zinc Oxide Films and Their Sensitivity to Humidity

In this study, the sensitivity of ZnO thin films to humidity is examined using an optical method. A precursor solution for ZnO film is prepared using the sol–gel process. Sensing elements were fabricated by spin coating different numbers of layers on separate prisms and subsequently annealing them. The sensing mechanism is the modulation of light intensity reflected from the glass–film interface as the relative humidity in the ambient air changes. The change in sensing with variation in number of layers is substantiated by theoretical calculations. Infrared studies, thermal gravimetric analysis, and differential thermal analysis of the precursor films was performed. The ZnO films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical transmission. SEMs studies confirm the presence of pores which are instrumental in adsorbing water vapour, thereby influencing the refractive index of the films. In the present opto-electronic sensing configuration described herein, a change of 0.09 RH% per unit change in emergent light intensity can be detected.

Fiber optical sensor for the determination of adulteration in petrol

The newly designed prism based fiber optical refractometer sensor has been used to determine adulteration in petrol. A procedure for identification of the adulterant and determination of its concentration in a sample of petrol has been reported. Substances like kerosene, diesel, a mixture of these two or of aviation gasoline and kerosene have been used as adulterants.

Prism-based fiber optical refractometer sensor

The new design for the prism based refractometer sensor presented here is characterized by its high sensitivity over a wide range of refractive indices of the ambient. The refractometer is more robust and user friendly than other such refractometers reported in literature.

Blue shift in optical band gap of sol–gel derived Sn1−xZnxO2 polycrystalline thin films

Undoped and Zn doped SnO2 thin films are deposited by sol–gel spin coating on glass substrate. XRD spectra with prominent peaks along (110) and (101) planes shows the polycrystalline nature of thin films. The particle size lies between 9.30 and 42.09xa0nm as estimated by Debye–Scherer method. SEM micrographs of the films contain pebble like structures spread throughout whose diameter decreases with increase in dopant concentration. Surface topology of the films is studied by atomic force microscopy. Transmission spectra show that all the films are highly transparent in the visible and IR spectral region (80–90xa0%) and a sharp absorption occurs near 300xa0nm. Approximately a change of 4xa0% is observed in the optical band gap by Zn doping. The optical band gap is tunable between 3.55 and 3.68xa0eV for 0xa0≤xa0xxa0≤xa00.15 in nanocrystalline Sn1−xZnxO2. Broad UV emission at 395xa0nm is observed in photoluminescence spectra of the films along with a blue emission. Emission intensity decreases as amount of Zn incorporated into SnO2 increases.