Sajan, D George; Rajesh, K; Warrier, K G K; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(October 29, 2011)
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Abstract:
The laser induced non-destructive photoacoustic technique has been employed
to measure the thermal diffusivity of lanthanum phosphate ceramics prepared
by the sol–gel route. The thermal diffusivity value was evaluated by knowing
the transition frequency between the thermally thin to thermally thick region
from the log–log plot of photoacoustic amplitude versus chopping frequency.
Analysis of the data was carried out on the basis of the one-dimensional
model of Rosencwaig and Gersho. The present investigation reveals that the
sintering temperature has great influence on the propagation of heat carriers
and hence on the thermal diffusivity value. The results were interpreted
in terms of variations in porosity with sintering temperature as well as with
changes in grain size.
Rani, Joseph(American Institute of Physics, January 13, 2007)
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Abstract:
Poly(methyl)methacrylate was made photoconducting by molecular doping and the
photoconductivity was investigated using modulated photocurrent technique . Low-temperature
current-voltage measurements showed that the transport mechanism was thermally activated
hopping. An experimental investigation of the photoconductivity action spectrum along with
theoretical calculation enabled an estimation of the diffusion coefficient of the material. The
presence of states with a distribution of lifetimes could be understood from the frequency response
of the photocurrent . The photocurrent was due to the field-assisted dissociation of these states
Sudha Kartha, C(American Institute of Physics., January 13, 2007)
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Abstract:
Poly(methyl)methacrylate was made photoconducting by molecular doping and the
photoconductivity was investigated using modulated photocurrent technique . Low-temperature
current-voltage measurements showed that the transport mechanism was thermally activated
hopping. An experimental investigation of the photoconductivity action spectrum along with
theoretical calculation enabled an estimation of the diffusion coefficient of the material. The
presence of states with a distribution of lifetimes could be understood from the frequency response
of the photocurrent . The photocurrent was due to the field-assisted dissociation of these states.
Syamala,S B; Dr.Sudha Kartha,C(Cochin University of Science & Technology, January , 2004)
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Abstract:
Photoconductivity (PC) processes may
be the most suitable technique for obtaining information about the states in the
gap. It finds applications in photovoItaics, photo detection and radiation
measurements. The main task in the area of photovoltaics, is to increase the
efficiency of the device and also to develop new materials with good optoelectronic
properties useful for energy conversion, keeping the idea of cost
effectiveness. Photoconduction includes generation and recombination of carriers
and their transport to the electrodes. So thermal relaxation process, charge
carrier statistics, effects of electrodes and several mechanisms of recombination
are involved in photoconductivity.A major effect of trapping is to make the experimentally observed decay
time of photocurrent, longer than carrier lifetime. If no trapping centers are
present, then observed photocurrent will decay in the same way as the density
of free carriers and the observed decay time will be equal to carrier lifetime. If
the density of free carriers is much less than density of trapped carriers, the
entire decay of photocurrent is effectively dominated by the rate of trap emptying
rather than by the rate of recombination.In the present study, the decay time of carriers was measured using
photoconductive decay (PCD) technique. For the measurements, the film was
loaded in a liquid Helium cryostat and the temperature was controlled using
Lakshore Auto tuning temperature controller (Model 321). White light was
used to illuminate the required area of the sample. Heat radiation from the light
source was avoided by passing the light beam through a water filter. The decay current. after switching off the illumination. was measured using a Kiethely
2000 multi meter. Sets of PCD measurements were taken varying sample
temperature, sample preparation temperature, thickness of the film, partial
pressure of Oxygen and concentration of a particular element in a compound.
Decay times were calculated using the rate window technique, which is a decay
sampling technique particularly suited to computerized analysis. For PCD curves
with two well-defined regions, two windows were chosen, one at the fast decay
region and the other at the slow decay region. The curves in a particular window
were exponentially fitted using Microsoft Excel 2000 programme. These decay
times were plotted against sample temperature and sample preparation
temperature to study the effect of various defects in the film. These studies
were done in order to optimize conditions of preparation technique so as to get
good photosensitive samples. useful for photovoltaic applications.Materials selected for the study were CdS, In2Se3, CuIn2Se3 and CuInS2•
Photoconductivity studies done on these samples are organised in six chapters
including introduction and conclusion.
Description:
Department of Physics,
Cochin University of Science and Technology
The heterogeneous photocatalytic degradation of methylorange over TiO2 is studied
and is found to be cost effective. Effect of Zirconium metal incorporation over titania system is investigated. Photocatalytic degradation of methylorange using solar radiation is
found to be highly economical when compared with the processes using artificial UV
radiation, which require substantial electrical power input. The characterization of titania as
well as modified zirconium metal doped titania systems are done using XRD, FTIR and
EDAX measurements. The catalytic activities of different systems are also compared and is
tried to correlate with the crystallite size and presence of dopant metal.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(IOP, 1994)
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Abstract:
Laser-induced photoelectric and photoemission optogalvanic effects in a Ne-Nd hollow cathode discharge have been studied using a continuous wave laser source. The potential barrier for photoinduced electron emission from the cathode decreases as the applied voltage is increased. Owing to secondary electron emission in the plasma, the photocurrent is greater than that without discharge. The multiplication of secondary electrons and the quantum efficiency are also investigated.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(Elsevier, August 1, 1995)
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Abstract:
The photoemission optogalvanic (POG) effect has been investigated in a neon-neodymium hollow cathode discharge using
cw laser excitation. Both positive and negative effects were observed. It was found that the amplitude of the POG signal was
unstable near the instability region of the discharge.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(IOP, 1993)
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Abstract:
A two-photon induced photoemission optogalvanic effect which brings about a change in the discharge voltage when a pulsed dye laser beam is focused on a tungsten electrode has been described. The experiment is performed with N2, NO2 and Ar discharges. The magnitude of the signal voltage is studied as a function of laser energy and discharge current. The effective quantum efficiency in the discharge is found to be larger than that in the vacuum condition.
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(IOP, 1993)
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Abstract:
A two-photon induced photoemission optogalvanic effect which brings about a change in the discharge voltage when a pulsed dye laser beam is focused on a tungsten electrode has been described. The experiment is performed with N2, NO2 and Ar discharges. The magnitude of the signal voltage is studied as a function of laser energy and discharge current. The effective quantum efficiency in the discharge is found to be larger than that in the vacuum condition.
Ajith Prasad, K C; Nampoori, V P N; Vallabhan, C P G(Elsevier, 1996)
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Abstract:
Photoemission optogalvanaic (POG) effect has been observed by irradiating copper target electrode, in a nitrogen discharge cell using 1.06 μm and frequency doubled 532 nm Nd:YAG laser pulse. Measurement of the nature of the variation of POG signal strength with 532 nm laser fluence confirms the two photon induced photoelectric emission from copper. However, using 1.06 μm laser pulses thermally assisted photoemission is observed.
Shali, N B; Sugunan, S(Springer Netherlands, 2007)
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Abstract:
Lanthana modified sol-gel titania is prepared
through particulate sol-gel route and the physico-chemical
characterizations of the prepared systems were done using
X-Ray diffration, EDX, BET surface area-pore volume measurements
and TG-DTG analysis. Benzophenone was observed
to be the sole product in the TiO2 photocatalyzed
oxidation of benzhydrol in oxygen purged acetonitrile. The
influence of various parameters, like irradiation time, amount
of catalyst, concentration of the catalyst and other factors on
the photocatalytic oxidation has been investigated. The proposed
mechanism envisages the involvement of a superoxide
radical anion.
ZnO micro particles in the range 0.4-0.6 μm were synthesized by microwave irradiation
method. The XRD analysis reveals that the sample is in the wurtzite phase with orientation
along the (101) plane. SAED pattern of the sample reveals the single crystalline nature of
the micro grains. TEM images show the formation of cylindrical shaped ZnO micro
structures with hexagonal faces. The optical phonon modes were slightly shifted in the
Raman spectrum,attributed to the presence of various crystalline defects and laser induced
local heating at the grain boundaries. A broad transmission profile was observed in the
FTIR spectrum from 1550-3400 cm-1 which falls in the atmospheric transparency window
region. PL spectrum centered at 500 nm with a broad band in the region 420-570 nm
comprised of different emission peaks attributed to transition between defect levels.
Various emission levels in the sample were expliained with a band diagram
Description:
Journal of Optoelectronics and Biomedical Materials Vol. 4, Issue 1, January-March 2012, p. 1 - 7
Junaid, Bushiri M; Saji, Chacko; Vaidyan, V K(IOP Publishing LTD, October 20, 2006)
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Abstract:
SnO2 nanocrystalline thin films were deposited on glass substrates by the
spray pyrolysis technique in air atmosphere at 375, 400, 425, 450 and
500 ◦C substrate temperatures. The obtained films were characterized by
using XRD. The room temperature photoluminescence (PL) spectra of these
films have near band edge (NBE) and deep level emission under the
excitation of 325 nm radiation. NBE PL peak intensity decreased
consistently with temperatures for samples prepared at 400, 450 and 500 ◦C,
while a sudden reduction in intensity is observed for the sample prepared at
425 ◦C. A similar effect was observed for the optical transmittance spectra.
These effects can be explained on the basis of the change in population of
oxygen vacancies as indicated by the change in a values
Lyjo, Joseph K; Dayas, K R; Soniya, Damodar; Bindu, Krishnan; Krishnankutty, K; Nampoori, V P N; Radhakrishnan, P(Elsevier, December 15, 2008)
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Abstract:
The laser-induced luminescence studies of the rare earth titanates (R2Ti2O7) (R = La, Nd and Gd) using 355 nm radiation from an Nd:YAG laser are presented. These samples with submicron or nanometer size are prepared by the self-propagating high temperature synthesis (SHS) method and there is no known fluorescence shown by these rare earths in the visible region. Hence, the luminescence transitions shown by the La2Ti2O7 near 610 nm and Gd2Ti2O7 near 767 nm are quite interesting. Though La3+ ions with no 4f electrons have no electronic energy levels that can induce excitation and luminescence processes in the visible region, the presence of the Ti3+ ions leads to luminescence in this region.