Vaidya Jayathirtha Rao

SEMICONDUCTING GAS SENSOR FOR CHLORINE BASED ON INVERSE SPINEL NICKEL FERRITE

Abstract Nickel ferrite, a p-type semiconducting oxide with an inverse spinel structure has been used as a gas sensor to selectively detect chlorine in air. This compound was prepared by two different routes namely, the citrate and co-precipitation method and sensor properties of the resulting compounds from both the methods were compared. X-ray diffraction was used to confirm the structure. The gas sensing characteristics were obtained by measuring the sensitivity as a function of various controlling factors like dopant, concentration of the dopant, operating temperature, concentration of the gas and finally the response time. The sensitivity to chlorine has been compared with that of other interfering gases. A probable explanation has been proposed to explain the selective sensitivity to oxidising gases like chlorine.

High sensitivity and selectivity of an SnO2 sensor to H2S at around 100 °C

Abstract The effect of preparation conditions on the sensitivity of tin-oxide-based semiconducting gas sensors has been studied by appropriately engineering the base material. The incorporation of CuO as an additive has significantly improved the sensing character of the sensor element. These sensor elements have been made sensitive to low concentrations (about 10 ppm and less) of hydrogen sulphide in air. Further, the operating temperature for maximum sensitivity has been considerably reduced to about 90–100 °C. These elements have been tested for cross sensitivity to other gases and confirmed unambiguously to be specifically sensitive to H 2 S, which is detected with maximum sensitivity. A plausible mechanism is proposed to explain this behaviour.

SnO2:Bi2O3 based CO sensor: Laser-Raman, temperature programmed desorption and X-ray photoelectron spectroscopic studies

Abstract The sensitivity and selectivity of tin oxide (SnO2) based gas sensors towards carbon monoxide (CO) was improved by doping the base material with Bi2O3 and Sb2O3. Laser-Raman studies of the compound confirm the formation of bismuth stannate (Bi2Sn2O7) above 800°C, which seems to be acting as a molecular sieve allowing only CO gas to react with the sensor surface, thereby imparting selectivity to the sensor. The chemisorption of oxygen on SnO2:Bi2O3 was investigated over a wide range of temperatures from room temperature to 800°C by means of Temperature Programmed Desorption (TPD) and X-ray Photoelectron Spectroscopic (XPS) studies which were carried out to establish the exact chemical species present on the sensor surface before and after the reaction.

LIQUID-PETROLEUM-GAS SENSOR BASED ON A SPINEL SEMICONDUCTOR, ZNGA2O4

Abstract A liquid-petroleum gas sensor has been developed with high selectivity and sensitivity based on an oxygen deficient spinel semiconductor, ZnGa2O4. The operating temperature of the sensor element has been optimised under different operating conditions. Palladium doped zinc gallate sensor, on exposure to LPG at about 320°C showed a change of 4–5 orders in the resistance. The response time also decreases from about 20 min in virgin ZnGa2O4 to less than 1 min in the palladium doped element. The electronic interaction between additive and semiconductor is proposed to account for the sensitisation effects in the sensor element.

Phosphine oxide functionalized pyrenes as efficient blue light emitting multifunctional materials for organic light emitting diodes

In a search for blue light emitting multifunctional materials, the electron transport enhancing diphenyl phosphine–oxide (Ph2PO) group has been appended to blue light emitting pyrene derivatives. This design, we observe, leads to highly efficient electron transporting blue-emitters for non-doped organic light emitting devices (OLEDs) with good film formation characteristics. The superior performance is attributed to enhanced charge transport and formation of pyrene excimers assisted by thermally activated delayed fluorescence (TADF) in the device. We report the synthesis and characterization using experimental and computational methods of six such pyrene derivatives. Although three of these derivatives show quenching of luminescence in solvents at higher concentrations, in the thin film invariably all six of them exhibit typical pyrene excimer emission. X-ray crystal analysis reveals π–π stacking and the C–H⋯O interactions in the solid due to the PO group. The measured electron mobilities for all the compounds are higher in comparison to the standard electron transport material, Alq3. Non-doped OLEDs with the pyrene derivatives as emitters (multi-layer configuration) as well as electron transport cum emitters (bilayer configuration) exhibit excellent efficiencies. The derivatives as emitters display a performance with current efficiencies (ηc) in the range 21.1–30.1 cd A−1, power efficiencies (ηp) 11.0–15.76 lm W−1, external quantum efficiencies (EQE) 7.2–9.1% and brightness 28 500–42 750 cd m−2. In addition, the derivatives as electron transporting emitters demonstrate very good external quantum efficiencies in the range of 3.0–4.0%. These results demonstrate a successful strategy to obtain blue light emitting multifunctional materials for OLED applications.

A novel FRET ‘off–on’ fluorescent probe for the selective detection of Fe3+, Al3+ and Cr3+ ions: Its ultrafast energy transfer kinetics and application in live cell imaging

A rhodamine-naphthalimide dyad probe, 1, that selectively responds to the addition of trivalent metal ions (Fe(3+) or Al(3+) or Cr(3+)) via ultrafast Förster resonance energy transfer (FRET) from naphthalimide to rhodamine is designed and synthesized. 1 is highly selective to the trivalent metal ions and the presence of other monovalent or divalent metal ions do not affect its detection ability. The probe is highly sensitive and it can respond to the presence of trivalent metal ions even at sub-micromolar levels. 1 is stable over a broad range of pH, non-toxic under experimental conditions and suitable to the fluorescence bio-imaging of live cells exposed to trivalent metal ions. The trivalent metal ion induced ultrafast energy transfer kinetics of 1 is explored using time resolved fluorescence experiments.

SnO2 / Bi2 O 3: A Suitable System for Selective Carbon Monoxide Detection

An SnO 2 based gas sensor composition with Bi 2 O 3 and Sb 2 O 3 is shown to respond selectively to CO gas even in the presence of other gases. X-ray diffraction and laser-Raman studies of the compound confirm the formation of bismuth stannate (Bi 2 Sn 2 O 7 ) above 800°C, which seems to act as a molecular sieve. The operating temperature for maximum sensitivity is around 200°C. Temperature programmed desorption studies were conducted to determine the nature of oxygen species adsorbed on the semiconductor surface responsible for the gas sensing.

Synthesis and biological evaluation of tetrazole containing compounds as possible anticancer agents

A series of new tetrazole derivatives are synthesized from Baylis–Hillman allyl amines in a clean, efficient and straightforward manner. The stereochemistry of the double bond is confirmed by X-ray diffraction data. These compounds are evaluated for in vitro anticancer activity against five cancer cell lines. Most of the compounds exhibited good anticancer activity in micro molar concentration out of 16 compounds synthesized and screened. Furthermore, the compound 5o has good binding affinity to calf thymus DNA (ct DNA), as assayed by UV-vis absorption and fluorescence spectroscopic methods.

X-ray photoelectron spectroscopic studies of noble metal-incorporated BaSnO3 based gas sensors☆

Abstract Barium stannate, a semiconducting oxide with cubic perovskite structure prepared by the thermal decomposition method, was incorporated with different noble metal additives. The gas sensing behavior of these materials to various reducing gases like liquefied petroleum gas (LPG), CH 4 and CO have been studied. The gas sensing characteristics established a relation between the sensitivity of the sensor to the different test gases and the work function of the noble metal additive. The results suggest that the greater the work function of the additive, the greater the depletion width of the semiconductor in air and the higher the sensitivity to the reducing gas. X-ray photoelectron spectroscopy studies have been carried out to understand the mechanism of sensing in these oxides. It has been established that in the case of Pd and Ag-incorporated BaSnO 3 it is predominantly the electronic sensitization through a direct interaction between these metals and the semiconductor surface, while in case of Pt-incorporated BaSnO 3 it is the chemical interaction which plays the major role in the gas sensing reaction.

Noble metal additive modulation of gas sensitivity of BaSnO3, explained by a work function based model

Barium stannate, a semiconducting oxide with cubic perovskite structure, has been prepared by the thermal decomposition method. Of its several applications, this material has proved to be one of the successful candidates for chemical sensors to detect toxic and inflammable gases. BaSnO 3 was incorporated with different noble metal additives and the gas sensing behavior of these materials to various reducing gases like LPG, CO and CH 4 have been studied. A model for the electronic interaction between additives and semiconducting BaSnO 3 gas sensors is discussed. The model is based on the depletion layer that is created due to metal-semiconducting oxide contact. Change of the gas sensor characteristics before and after the exposure to the different test gases has been explained on the basis of work function of metal additives. The valence band X-ray photoelectron spectroscopy studies were used to support the results on the gas sensing characteristics in each of the noble metal incorporated BaSnO 3 sensor materials and bring out the difference in the sensing mechanisms in these materials.