Low-voltage driven ZnS:Mn MIS and MISIM thin film electroluminescent devices with Eu2O3 insulator layer

AC thin film electroluminescent devices of MIS and MISIM have been fabricated with a novel dielectric layer of Eu2O3 as an insulator. The threshold voltage for light emission is found to depend strongly on the frequency of excitation source in these devices. These devices are fabricated with an active layer of ZnS:Mn and a novel dielectric layer of Eu2O3 as an insulator. The observed frequency dependence of brightness-voltage characteristics has been explained on the basis of the loss characteristic of the insulator layer. Changes in the threshold voltage and brightness with variation in emitting or insulating film thickness have been investigated in metal-insulator-semiconductor (MIS) structures. It has been found that the decrease in brightness occurring with decreasing ZnS layer thickness can be compensated by an increase in brightness obtained by reducing the insulator thickness. The optimal condition for low threshold voltage and higher stability has been shown to occur when the active layer to insulator thickness ratio lies between one and two.

Long period gratings in multimode optical fibers: application in chemical sensing

We propose and demonstrate a new technique for evanescent wave chemical sensing by writing long period gratings in a bare multimode plastic clad silica fiber. The sensing length of the present sensor is only 10 mm, but is as sensitive as a conventional unclad evanescent wave sensor having about 100 mm sensing length. The minimum measurable concentration of the sensor reported here is 10 nmol/l and the operating range is more than 4 orders of magnitude. Moreover, the detection is carried out in two independent detection configurations viz., bright field detection scheme that detects the core-mode power and dark field detection scheme that detects the cladding mode power. The use of such a double detection scheme definitely enhances the reliability and accuracy of the results. Furthermore, the cladding of the present fiber need not be removed as done in conventional evanescent wave fiber sensors.

Synthesis and Characterisation of Zinc Gallate Based Phosphors for Thin Film Electroluminescent Devices

Department of Physics, Cochin University of Science and Technology

Design and development of an LED based fiber optic evanescent wave sensor for simultaneous detection of chromium and nitrite traces in water

The design and development of a cost-effective, simple, sensitive and portable LED based fiber optic evanescent wave sensor for simultaneously detecting trace amounts of chromium and nitrite in water are presented. In order to obtain the desired performance, the middle portions of two multimode plastic clad silica fibers are unclad and are used as the sensing elements in the two arms of the sensor. Each of the sensor arms is sourced by separate super bright green LEDs, which are modulated in a time-sharing manner and a single photo detector is employed for detecting these light signals. The performance and characteristics of this system clearly establish the usefulness of the technique for detecting very low concentrations of the dissolved contaminants.

Drought Climatology of Indo-Gangetic Region of India Using Remote Sensing and Crop Growth Simulation Models

Department of Atmospheric Sciences, Cochin University of Science and Technology

HRTEM assessment of Wurtzite and Zinc-Blende phases in GaAs nanowires for optoelectronic devices

Màster en Nanociència i Nanotecnologia. Curs 2007-2008. Directors: Francesca Peiró i Martínez and Jordi Arbiol i Cobos

Ferrofluid thin films as optical gaussmeters proposed for field and magnetic moment sensing

Ferrofluids belonging to the series, Ni x Fe1-x Fe2O4 and Zn x Fe1-x Fe2O4, were synthesized using cold co-precipitation. Liquid films of these ferrofluids were prepared by encapsulating the ferrofluids in between two optically smooth and ultrasonically cleaned glass plates. Magnetic field induced laser transmission through these ferrofluid films has been investigated. Magnetic field values can be calibrated in terms of output laser power in the low field region in which the variation is linear. This set up can be used as a cheap optical gaussmeter in the low field regime. Using the same set-up, the saturation magnetization of the sample used can also be calculated with a sample that is pre-characterized. Hence both magnetization of the sample, as well as applied magnetic field can be sensed and calculated with a precalibrated sample.

Synthesis, Growth and Characterization of Oxide Phosphors for Thin Film Electroluminescent Devices

Department of Physics, Cochin University of Science and Technology

Energy Management in Wireless Sensor Networks: A Crosslayer,Channel Adaptive Approach Towards Performance Optimization

The proliferation of wireless sensor networks in a large spectrum of applications had been spurered by the rapid advances in MEMS(micro-electro mechanical systems )based sensor technology coupled with low power,Low cost digital signal processors and radio frequency circuits.A sensor network is composed of thousands of low cost and portable devices bearing large sensing computing and wireless communication capabilities. This large collection of tiny sensors can form a robust data computing and communication distributed system for automated information gathering and distributed sensing.The main attractive feature is that such a sensor network can be deployed in remote areas.Since the sensor node is battery powered,all the sensor nodes should collaborate together to form a fault tolerant network so as toprovide an efficient utilization of precious network resources like wireless channel,memory and battery capacity.The most crucial constraint is the energy consumption which has become the prime challenge for the design of long lived sensor nodes.

Remote Sensing the Signatures of Upwelling in South Eastern Arabian Sea

In this thesis, a variety of available satellite data products have been made use of to bring out a synergistic analysis on the upwelling phenomenon in SEAS. Basic concepts of remote sensing, upwelling and linked oceanography topics have been dealt in this work .Auxiliary data products utilized in this study are described in chapter 2. The climatological monthly variability of the upwelling signatures are detailed under chapter 3. Chapter 4 presents the forcing factors that trigger the upwelling process in SEAS. Chapter 5 describes the oceanic response to the forcing factors with respect to the SST cooling and CHLA blooms. Chapter 6 presents the heat budget of the region and the variability of heat budget terms with respect to upwelling. Chapter 7 describes the inter-annual variability of upwelling intensity in SEAS and the influence of climatic events on upwelling.

Fabrication and the study of zinc sulphide based electroluminescent devices

This thesis contains the author's work in preparing efficient EL phosphors, the details of fabrication of low voltage operated thin film EL (TFEL) devices and DC TFEL devices. Some of the important work presented here are related to the white light emitting ZnS:Cu,Pr,Cl phosphor which can be colour tuned by changing the excitation frequency, observation of energy transfer from Cu/Ag ions to rare earth ions in ZnS:(Cu/Ag), RE,Cl phosphors, development of TFEL device which can be operated below 50V, optimization of the device parameters for long life, high brightness in terms of the active and insulating layer thicknesses, observation of dependence of threshold voltage for the onset of emission on frequency of excitation when a novel dielectric Eu2O3 film was used as insulator and the devices with multicolor emission using ZnS doped with rare earth as active layer. Characterization based on other devices based on ZnS:Sm, ZnS:Pr, ZnS:Dy and their emission characteristics are also illustrated

Studies on electroluminescence using Powder and thin film devices

The subject of electroluminescence has currently acquired great importance because of its potential applications in display systems of a wide variety. A large number of scientists working in commercial, governmental as well as academic institutions all over the world are at present engaged in the intense effort to develop new and efficient phosphor materials and electroluminescent devices. This thesis presents the work carried out by the author in this field during the past few years. The studies discussed in this thesis are mostly confined to the development of some new phosphor materials, their uses in powder and thin film electroluminescent devices and to their electrical and spectral characteristics. Care has been taken to bring' out the physics involved in all the above aspects of the phenomenon

Development of optical fiber sensors for selected chemical and physical sensing applications

The objective of the preset work is to develop optical fiber sensors for various physical and chemical parameters. As a part of this we initially investigated trace analysis of silica, ammonia, iron and phosphate in water. For this purpose the author has implemented a dual wavelength probing scheme which has many advantages over conventional evanescent wave sensors. Dual wavelength probing makes the design more reliable and repeatable and this design makes the sensor employable for concentration, chemical content, adulteration level, monitoring and control in industries or any such needy environments. Use of low cost components makes the system cost effective and simple. The Dual wavelength probing scheme is employed for the trace analysis of silica, iron, phosphate, and ammonia in water. Such sensors can be employed for the steam and water quality analysers in power plants. Few samples from a power plant are collected and checked the performance of developed system for practical applications.

Blue, Green and Orange-Red Light Emitting Polymers: Synthesis, Characterization and Prospects of Applications in Optoelectronic Devices

Light emitting polymers (LEPs) are considered as the second generation of conducting polymers. A Prototype LEP device based on electroluminescence emission of poly(p-phenylenevinylene) (PPV) was first assembled in 1990. LEPs have progressed tremendously over the past 20 years. The development of new LEP derivatives are important because polymer light emitting diodes (PLEDs) can be used for the manufacture of next-generation displays and other optoelectronic applications such as lasers, photovoltaic cells and sensors. Under this circumstance, it is important to understand thermal, structural, morphological, electrochemical and photophysical characteristics of luminescent polymers. In this thesis the author synthesizes a series of light emitting polymers that can emit three primary colors (RGB) with high efficiency

Studies On The Electrical Properties Of Some Crystalline Organic Compounds And Conducting Polymers

Solid electrolytes for applications like chemical sensing, energy storage, and conversion have been actively investigated and developed since the early sixties. Although of immense potential, solid state protonic conductors have been ignored in comparison with the great interest that has been shown to other ionic conductors like lithium and silver ion conductors. The non-availability of good, stable protonic conductors could be partly the reason for this situation. Although organic solids are better known for their electrical insulating character, ionic conductors of organic origin constitute a recent addition to the class of ionic conductors. However, detailed studies (N1 such conductors are scarce. Also the last decade has witnessed an unprecedented boom in research on organic "conducting polymers". These newly devised materials show conductivity spanning from insulator to metallic regimes, which can be manipulated by appropriate chemical treatment. They find applications in devices ranging from rechargeable batteries to "smart windows". This thesis mainly deals with the synthesis and investigations on the electrical properties of (i) certain organbc protonic conductors derived from ethylenediamine and (ii) substituted polyanilines