Narendra Verma - Academia.edu (original) (raw)
Papers by Narendra Verma
Ndt & E International, 2006
This paper presents a technique for detection and measurement of vibrations especially in machine... more This paper presents a technique for detection and measurement of vibrations especially in machine design. This technique makes use of a He-Ne laser and has decisively an edge over the conventional methods, which have certain limitations regarding their vibration measurements due to their contact nature. However, in the present study, the method used is a non-contact one. In this case, the measurements include variation of voltage amplitude with rotor speed and variation of vibration frequency with rotor speed. Calibration studies are also conducted. q
Journal of Nanoparticle Research
To exploit the photoluminescent behavior of CdS at nanoscale with different doping concentration ... more To exploit the photoluminescent behavior of CdS at nanoscale with different doping concentration of europium—a rare earth element, we report the synthesis of Eu-doped CdS nanorods by using low temperature solvothermal process by using ethylenediamine. The outcomes can have future applications as phosphors, photovoltaic cells, lasers, light emitting diodes, bio-imaging, and sensors. The doping was confirmed by electron dispersive spectroscopy supported by X-ray diffraction. From scanning electron microscopy and transmission electron microscopy analysis it was observed that the average diameter of the Cd1−x Eux S nanorods is about 10–12 nm having lengths in the range of 50–100 nm. UV–Visible spectroscopy study was carried out to determine the band gap of the nanorods and the absorbance peaks showed blue shift with respect to the bulk CdS. The blue shift was also observed as the doping concentration of Eu increases. From photoluminescence (PL) studies at λex = 450 nm, peaks at 528 and 540 nm were observed due to CdS, peak at 570 nm is due to defects related transitions, while the peak at 613 nm is due to Eu. As the doping concentration of Eu is increased the intensity of the luminescent peak at 613 nm is increased. Thermogravimetric analysis showed the nanorods are thermally stable up to 300 °C. The traces of impurities adsorbed on the nanorods were confirmed by Fourier transform infrared spectroscopy.
Ndt & E International, 2006
This paper deals with the calculation of various parameters such as dispersion, absorption and pe... more This paper deals with the calculation of various parameters such as dispersion, absorption and permittivity of synthetic insulation paper to see the effect of frequency and thermal aging to be used in various industrial applications. Firstly the calculations were made for a fresh sample and then for the samples, which were aged at three different times and temperatures. These calculations were done using the earlier reported data [1] of capacitance and loss factor. The studies showed that with the increase in frequency the dispersion, absorption and permittivity of the samples decrease, however, with aging (increasing time and decreasing temperature) the values of dispersion, absorption and permittivity increase at any fixed frequency.
Journal of Nanoparticle Research, 2009
Eu3+-doped Cd1−x Znx S (0 ≤ x ≤ 0.5) quantum dots (QDs) have been synthesized using wet chemical ... more Eu3+-doped Cd1−x Znx S (0 ≤ x ≤ 0.5) quantum dots (QDs) have been synthesized using wet chemical precipitation method. X-ray diffraction and transmission electron microscope have been used for the crystallographic and morphological characterization of synthesized nanomaterials. In order to understand the spectral characteristics of doped QDs, N2-laser induced time resolved spectra have been recorded. Excited state lifetime values for dichromatic emission (red and violet) attributed to 5D0 → 7FJ (J = 1, 2) transitions of Eu3+ and host lattice transitions have been calculated from the recorded luminescence decay curves. Decay time dependence on the dopant concentration (0.01–10 at. wt% of Cd2+) has been studied in detail.
Ndt & E International, 2006
This paper presents a technique for detection and measurement of vibrations especially in machine... more This paper presents a technique for detection and measurement of vibrations especially in machine design. This technique makes use of a He-Ne laser and has decisively an edge over the conventional methods, which have certain limitations regarding their vibration measurements due to their contact nature. However, in the present study, the method used is a non-contact one. In this case, the measurements include variation of voltage amplitude with rotor speed and variation of vibration frequency with rotor speed. Calibration studies are also conducted. q
Journal of Nanoparticle Research
To exploit the photoluminescent behavior of CdS at nanoscale with different doping concentration ... more To exploit the photoluminescent behavior of CdS at nanoscale with different doping concentration of europium—a rare earth element, we report the synthesis of Eu-doped CdS nanorods by using low temperature solvothermal process by using ethylenediamine. The outcomes can have future applications as phosphors, photovoltaic cells, lasers, light emitting diodes, bio-imaging, and sensors. The doping was confirmed by electron dispersive spectroscopy supported by X-ray diffraction. From scanning electron microscopy and transmission electron microscopy analysis it was observed that the average diameter of the Cd1−x Eux S nanorods is about 10–12 nm having lengths in the range of 50–100 nm. UV–Visible spectroscopy study was carried out to determine the band gap of the nanorods and the absorbance peaks showed blue shift with respect to the bulk CdS. The blue shift was also observed as the doping concentration of Eu increases. From photoluminescence (PL) studies at λex = 450 nm, peaks at 528 and 540 nm were observed due to CdS, peak at 570 nm is due to defects related transitions, while the peak at 613 nm is due to Eu. As the doping concentration of Eu is increased the intensity of the luminescent peak at 613 nm is increased. Thermogravimetric analysis showed the nanorods are thermally stable up to 300 °C. The traces of impurities adsorbed on the nanorods were confirmed by Fourier transform infrared spectroscopy.
Ndt & E International, 2006
This paper deals with the calculation of various parameters such as dispersion, absorption and pe... more This paper deals with the calculation of various parameters such as dispersion, absorption and permittivity of synthetic insulation paper to see the effect of frequency and thermal aging to be used in various industrial applications. Firstly the calculations were made for a fresh sample and then for the samples, which were aged at three different times and temperatures. These calculations were done using the earlier reported data [1] of capacitance and loss factor. The studies showed that with the increase in frequency the dispersion, absorption and permittivity of the samples decrease, however, with aging (increasing time and decreasing temperature) the values of dispersion, absorption and permittivity increase at any fixed frequency.
Journal of Nanoparticle Research, 2009
Eu3+-doped Cd1−x Znx S (0 ≤ x ≤ 0.5) quantum dots (QDs) have been synthesized using wet chemical ... more Eu3+-doped Cd1−x Znx S (0 ≤ x ≤ 0.5) quantum dots (QDs) have been synthesized using wet chemical precipitation method. X-ray diffraction and transmission electron microscope have been used for the crystallographic and morphological characterization of synthesized nanomaterials. In order to understand the spectral characteristics of doped QDs, N2-laser induced time resolved spectra have been recorded. Excited state lifetime values for dichromatic emission (red and violet) attributed to 5D0 → 7FJ (J = 1, 2) transitions of Eu3+ and host lattice transitions have been calculated from the recorded luminescence decay curves. Decay time dependence on the dopant concentration (0.01–10 at. wt% of Cd2+) has been studied in detail.