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Tailoring optical properties of TiO_2 in silica glass for limiting applications

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Chinese physics B 2014年第3期23卷 303-307页

作者： S.Divya Indu Sebastian V.p.N.Nampoori p.radhakrishnan A.Mujeeb International School of photonics Cochin University of Science and Technology

We present the linear and nonlinear optical studies on TiO2-SiO2 nanocomposites with varying compositions. Opti- cal band gap of the material is found to vary with the amount of SiO2 in the composite. The phenomenon of two-photon absorption （TpA） in TiO2/SiO2 nanocomposites has been studied using open aperture Z-scan technique. The nanocom- posites show better nonlinear optical properties than pure TiO2, which can be attributed to the surface states and weak dielectric confinement of TiO2 nanoparticles by SiO2 matrix. The nanocomposites are thermally treated and similar studies are performed. The anatase form of TiO2 in the nanocomposites shows superior properties relative to the amorphous and rutile counterpart. The involved mechanism is explained by rendering the dominant role played by the excitons in the TiO2 nanoparticles.

关键词： reverse saturable absorption (RSA) optical limiting excitons

Fabrication and photostability of Rhodamine-6G Gold Nanoparticle Doped polymer Optical Fiber

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Chinese physics Letters 2013年第11期30卷 180-183页

作者： Suneetha Sebastian Ajina C C.p.G Vallabhan V.p.N.Nampoori p.radhakrishnan M.Kailasnath International School of photonics Cochin University of Science and TechnologyCochin 22India

We report on fabrication of a rhodamine-6G-gold-nanoparticle doped polymer optical *** gold nanoparticle is synthesized directly into the monomer solution of the polymer using laser ablation synthesis in *** size of the particle is found from the transmission electron ***-6G is then mixed with the nanoparticle-monomer solution and optical characterization of the solution is *** is found that there is a pronounced quenching of fluorescence of rhodamine 6G due to fluorescence resonance energy *** monomer solution containing rhodamine 6G and gold nanoparticles is now made into a cylindrical rod and drawn into a polymer optical ***,the photostability is calculated with respect to the pure dye doped polymer optical fiber.

关键词： stability particle Rhodamine

Spectral Characterization of Laser Induced plasma from Titanium Dioxide

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plasma Science and Technology 2007年第4期9卷 456-459页

作者： V.J.DANN M.V.MATHEW V.p.N.NAMpOORI C.p.G.VALLABHAN V.M.NANDAKUMARAN p.radhakrishnan International School of photonics Cochin University of Science and TechnologyCochin 22India Centre of Excellence in Lasers and Optoelectronic SciencesCochin University of Science and TechnologyCochin 22India International School of photonics Cochin University of Science and TechnologyCochin 22India Centre of Excellence in Lasers and Optoelectronic Sciences Cochin University of Science and TechnologyCochin 22India

Optical emission from TiO2 plasma, generated by a nanosecond laser is spectroscopically analysed. The main chemical species are identified and the spatio-temporal distribution of the plasma parameters such as electron temperature and density are characterized based on the study of spectral distribution of the line intensities and their broadening characteristics. The parameters of laser induced plasma vary quickly owing to its expansion at low background pressure and the possible deviations from local thermodynamic equilibrium conditions are tested to show its validity.

关键词： laser induced plasma titanium dioxide optical emission spectroscopy local thermodynamic equilibrium

Improving the photocatalytic performance of TiO2 via hybridizing with graphene

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Journal of Semiconductors 2017年第6期38卷 24-31页

作者： K S Divya Athulya K Madhu T U Umadevi T Suprabha p.radhakrishnan Nair Suresh Mathew School of Chemical Sciences Mahatma Gandhi University Kottayam 686 560 Kerala India Advanced Molecular Materials Research Centre Mahatma Gandhi University Kottayam 686 560 Kerala India

In this paper an improvement in the photocatalytic performance of TiO2 was carried out via hybridizing with ***-TiO2（GR-TiO2/nanocomposites with different weight addition ratios of graphene oxide（GO）have been prepared via a facile microwave irradiation of GO and tetrabutyl titanate in isopropyl *** spectroscopy（RS）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,UV–visible spectroscopy（UV–vis）,Fourier transform infrared spectra（FTIR）,energy dispersive X-ray spectroscopy（EDX）and photoluminescence spectra（pL）are employed to determine the properties of the *** irradiation can heat the reactant to a higher temperature in a short time,simultaneously GO is reduced to graphene and TiO2 nanoparticles grown on the surface of ***-TiO2 nanocomposites synthesized via this approach have efficient electron conductivity in GR,resulting in a reduced electron–hole recombination *** the synthesized nanocomposites,GT-8wt% exhibited the best photocatalytic activity toward photocatalytic degradation of *** current work provides a new insight for the fabrication of GR-TiO2 nanocomposites within a short reaction time and also explains the mechanism of photocatalysis employing radical and hole scavengers.

关键词： graphene (GR) tetrabutyl titanate (TBT) GR-TiO2 nanocomposites methylene blue photocatalysis

A fiber optic biosensor for the detection of cholesterol levels based on chitosan coated long period grating

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Optoelectronics Letters 2016年第1期12卷 23-26页

作者： C.Bobby Mathews T.M.Libish B.Kaushalkumar V.Vivek Radhakrishna prabhu p.radhakrishnan International School of photonics Cochin University of Science and Technology Kochi 682022 India Muslim Educational Society Collegeof Engineering Kuttippuram 679573 India Robert Gordon University Aberdeen AB107QB UK

A fiber optic sensor for the measurement of total cholesterol is designed and *** developed chitosan coated long period grating(LpG) sensor shows a sensitivity of 5.025×106 pm·m L/g in the measurement range of the *** sensor also shows a linear response in the measured range of cholesterol levels,which is highly desirable for exploitation as a commercial cholesterol sensor.

关键词：胆固醇水平传感器检测长周期光栅壳聚糖纤维光学涂层生物传感器灵敏度

performance of polymer/CdS organic-inorganic hybrid LEDs

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Optoelectronics Letters 2016年第2期12卷 110-114页

作者： C.pradeep S.Mathew M.A.G.Namboothiry C.p.G.Vallabhan p.radhakrishnan V.p.N.Nampoori International School of photonics Cochin University of Science and Technology School of physics Indian Institute of Science Education and Research Department of Optoelectronics University of Kerala

Organic-inorganic hybrid light emitting diodes(LEDs) were fabricated by incorporating cadmium sulphide(Cd S) nanoparticles in hole transporting layer and light emitting materials of a polymer LED. The Cd S nanoparticles with size of 10 nm were synthesized by precipitation technique. The LEDs incorporated with the Cd S nanoparticles show a reduction in turn on voltage and luminance. When the nanoparticles are incorporated in a suitable fluorene based light emitting polymer, the luminance is increased along with the decrease of turn on voltage.

关键词： inorganic incorporated transporting blend cadmium coated hexagonal filtered adding attributed

Refractive index and temperature dependent displacements of resonant peaks of long period grating inscribed in hydrogen loaded SMF-28 fiber

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Optoelectronics Letters 2012年第2期8卷 101-104页

作者： T.M.Libish M.C.Bobby J.Linesh S.Mathew C.pradeep V.p.N Nampoori p.radhakrishnan International School of photonics Cochin University of Science and Technology S.C.T.College of Engineering

In this paper, the effects of refractive index (RI) of surrounding medium and ambient temperature on the transmission characteristics of a long period grating (LpG) are experimentally analyzed. The spectral behavior of LpG is investigated when the ambient index is higher or lower than that of the cladding material. The results show that the refractive index sensitivity of lower order attenuation bands is very low compared with that of the highest order attenuation band. But in the case of temperature, the lower order attenuation bands of the LpG can also exhibit good sensitivity like the higher-order bands.

关键词：长周期光栅温度依赖折射率共振峰光纤加载位移实验分析

Electronic and optical properties of TiO_2 and its polymorphs by Z-scan method

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Chinese physics B 2014年第8期23卷 340-344页

作者： S. Divya V p N Nampoori p.radhakrishnan A Mujeeb International School of photonics Cochin University of Science and Technology

TiO2 is a material which has attracted considerable attention from the scientific community for its innumerable prop- erties. TiO2 is known to exist in nature in three different crystalline structures： rutile, anatase, and brookite. Anatase and rutile TiO2 films have been widely characterized for their potential applications in solar cells, self-cleaning coatings, and photocatalysis. In the present report, the third-order nonlinear susceptibilities of TiO2 and its polymorphs, anatase, and rutile, prepared by the sol-gel technique followed by heat treatment are investigated using the Z-scan technique at a wavelength of 532 nm with a duration of 7 ns. Imaginary and real values of Z（3） for amorphous, anatase, and rutile are also calculated and found to be 5 × 10^-19 m2/V2, 27 × 10^-19 m2/V2, 19 × 10^-19 m2/V2, respectively. It is found that the values of the optical constants of amorphous TiO2 after heat treatment vary considerably. It is assumed that this could be due to the variation in the electronic structure of TiO2 synchronous with the formation of its polymorphs, anatase, and rutile. Amorphous TiO2 is marked by the localization of the tail states near the band gap, whereas its crystalline counterparts are characterized by completely delocalized tail states.

关键词： excitons reverse saturable absorption (RSA) excitonic nonlinearity

Coating configuration dependency of fiber optic silver coated U-bent plasmonic sensor surfaces in concentration sensing measurements

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Optoelectronics Letters 2018年第6期14卷 465-469页

作者： pRIYAMVADA V C AJINA C radhakrishnan p International School of photonics Cochin University of Science and Technology

The sensitivity of the plasmonic sensor surfaces can be enhanced significantly if the sensor region is bent to U shape. Here, an experimental verification is done to evaluate the performance variations of the U-bent plasmonic silver coated sensor surfaces with different coating orientations inside the vacuum coating chamber. The performances of uncoated, partially coated as well as fully coated optical fiber U-bent surfaces are analyzed. The results show that the coating configuration of the U-bent surfaces can affect the sensing property. A fully silver coated sensor region outperforms the other two types of sensor surfaces with better sensing capability.

关键词： Coating configuration dependency fiber optic silver coated U-bent plasmonic sensor surfaces