Electronics

Nanotechnology has led to a profound paradigm shift after the developments in recent
years and after being recognised as one of the most important areas of impending technology.
Nanomaterials are the basis of newly emerging nanotechnologies for various applications in
sensors, photonics, drug delivery, proteomics, biomolecular electronics, and homeland security.
Luminescent nanomaterials have attracted great interest worldwide because of their unusual
structural, optical and electronic properties as well as efforts to prepare miniaturised devices. By
understanding and manipulating these properties, the performance of the resulting optical structure
can be tailored for desired end-use applications. Luminescence nanoparticles have tremendous
potential in revolutionizing many interesting applications in today’s emerging cutting-edge optical
technology such as solid state lighting. Solid-state lighting (SSL) relies on the conversion of
electricity to visible white light using solid materials. SSL using any of the materials (inorganic,
organic, or hybrid) has the potential for unprecedented efficiencies. The development of novel
mercury-free inexpensive nanomaterials, that convert longer wavelength UV to blue light
eventually into white-light and are eco-friendly with improved luminous efficacy, energy-saving,
long-lifetime, and low-power consumption characteristics, is discussed. In this review, we present a
general description of EL related to nanomaterials as the emitter and outlines basic research
requirements that could enable solid-state lighting to achieve its potential. Continuing progress in
the synthesis and purification of SSL materials are beginning to enable separation of extrinsic and
intrinsic phenomena and improve device performance. This review mainly focuses on the basic
mechanism, classification, synthesis and characterization of luminescent nanomaterials. The review
also covers recent advances in lanthanide-based nanomaterials and photoluminescent nanofibers
formed by combining electrospun polymeric nanofibers and quantum dots (QDs) for lighting
applications. In spite of the remarkable scientific progress in preparation processes and applications
of nanomaterials, they are still not widely used by the industry. Finally, we conclude with a look at
the future challenges and prospects of the development of electroluminescence (EL) devices for
lighting.

Polymer solar cells belongs to promising class of next-generation photovoltaic, because they hold promise for the realization of mechanically flexible, lightweight, large-area devices that can be fabricated by room-temperature solution processing. High power conversion efficiencies of ~15% in tandem polymer solar cells based on semiconducting polymers are fabricated from solution-processing techniques and have unique prospects for achieving low-cost solar energy harvesting, owing to their material and manufacturing advantages. The potential applications of polymer solar cells are broad, ranging from flexible solar modules and semitransparent solar cells in windows, to building applications and even photon recycling in liquid-crystal displays. This review covers the scientific origins and basic properties of polymer solar cell technology, material requirements and device operation mechanisms, while also providing a synopsis of major achievements in the field over the past few years. Potential future developments and the applications of this technology are also briefly discussed.

II-VI semiconductor nanoparticles have recently attracted a lot of attention due to the possibility of their application in various devices. In the present study, chemical method has been used in synthesis of CdS nanoparticles and thiophenol was used as capping agent. X-ray diffraction studies of both samples were done. The dc conductivity of CdS increases at a lower rate or is approximately constant upto 500K and thereafter the conductivity increases at a rapid rate. Beyond T c it is seen that the portion of the σ dc versus 1000/T is almost a straight line showing an Arrehenious behaviour. The dielectric constant of nanoparticles of CdS is found to be larger than the corresponding values of CdS crystals. It is clearly observed that at lower wavelengths nanocrystalline samples show a blue-shift. The three peaks of sample (S2), A, Band C can be ascribed to the transition from Cd-O complex donor formed by adsorbed oxygen to the valance band, Cd-excess acceptor and the surface states, respectively.

In this letter, we demonstrate that luminance efficiency of polymer light emitting diode can be significantly enhanced by adding a small amount of ionic solid electrolytes. Heterojunction polymer device, consist of MEH-PPV, C 60 , methanofullerene([6,6}-phenyl C61-butyric acid methyl ester) PCBM and/or PEO as the active materials. It has been found that blending of ionic solid electrolytes, such as polyethylene oxide into active layer, enhances the luminance efficiency of polymer device. It is believed that the optimized polymer morphology improves carrier mobility of MEH-PPV.

Thin ®lm electroluminescence (TFEL) displays are complex optoelectronic devices with challenging material requirement. The electrical characteristics of ZnS : Mn alternating current thin ®lm electroluminescent devices grown by electron beam evaporation are assessed as function of voltage frequency and Mn concentration. The threshold voltage increases with increasing frequency of the applied voltage and saturation value of electroluminescence (EL) brightness increases linearly with the frequency of applied voltage. The EL brightness increases linearly with the frequency of the applied voltage. The EL brightness was found optimum for a particular activator concentration. A model is proposed and an expression is derived for the EL brightness, which is able to explain the dependence of the EL brightness on different parameters.

SHIKHA MISHRA, SAN JAY TIWARI* and BP CHANDRA Department of Post Graduate Studies and Research in Physics, RD University, Jabalpur 482 001, India *Department of Physics, Govt. Autonomous Science College, Jabalpur 482 001, India MS received 7 February ...

Indian Journal of Radio & Space Physics Vol. 39, June 2010, pp. 163-169 ... A dual-band stacked rectangular microstrip antenna ... Rajesh Kumar Vishwakarma$,* & Sanjay Tiwari# School of Studies in Electronics, Pt Ravishankar Shukla University, Raipur 492 010 (CG) E-mail: $ ...

In practice, the relative efficiencies of different crystals are often determined under identical conditions of temperature and excitation. If the temperature of a crystal is increased or decreased with respect to room temperature, luminescence efficiency may get increased or decreased according to the composition of the crystal. When coloured crystals of NaCl, NaBr, KCl and KBr are excited by pulse-induced excitation at different temperatures, the mechanoluminescence (ML) intensity increases with temperature. The ML intensity of first peak, I ml , second peak, I m2 and the total ML intensity, I T , initially increase with temperature and then tend to attain an optimum value for a particular temperature of crystals. The ratio, I m2 /I ml , is found to increase with increasing temperature of the crystals. The expression derived on the basis of rate equations, are able to explain the temperature dependence of ML intensity on several parameters.

In this letter, we demonstrate that luminance efficiency of polymer light emitting diode can be significantly enhanced by adding a small amount of ionic solid electrolytes. Heterojunction polymer device, consist of MEH-PPV, C 60 , methanofullerene([6,6}-phenyl C61-butyric acid methyl ester) PCBM and/or PEO as the active materials. It has been found that blending of ionic solid electrolytes, such as polyethylene oxide into active layer, enhances the luminance efficiency of polymer device. It is believed that the optimized polymer morphology improves carrier mobility of MEH-PPV.

Organic electronics is currently experiencing a surge of activities worldwide prompted in part by recent advances in achieving high electronic mobility, light emission over a broad range of frequencies, demonstration of spin valve operation with giant magneto-resistance and other effects. Despite these encouraging promises, there are many roadblocks that hinder a broader proliferation of "plastic electronics" in contemporary technology. Such devices involve charge transport as a main process in their operation processes, and therefore, require high-performance charge-transporting materials. The charge-carrier mobility is the major determining factor for the speed of electronic devices. Arguably, the most significant of them is the challenge to achieve a comprehensive understanding of the fundamentals of charge injection and charge transport in organics. In spite of its simple definition, because of the difficulty of measuring velocity, accurate determination of the mobility of the carriers is not easy and indirect ways are used, each with its own advantages and disadvantages. The article discusses important mobility measurement techniques employed for organic optoelectronic devices.

A numerical model for the electrical properties for polymeric light-emitting diodes (PLEDs) is presented which accounts for drift-and diffusion transport, recombination and re-emission processes. The current-voltage characteristics of single layer polymer lightemitting diodes are found to be dominated by the space-charge limited bulk hole-conductivity. The device efficiency is found to increase with bias as electron current is strongly reduced by injection barrier. The operating voltage increases with increased thickness of polymer layer. The understanding of these characteristics will facilitate the further optimization of the performance of polymer LEDs.

Polycrystalline films of CdTe were electroplated onto titanium substrates from acidic baths. When surface treated, these layers show good photoelectrochemical behaviour in a polysulphide electrolyte with high conversion efficiencies and stability. The solid state parameters of the films annealed are calculated and compared with those of unannealed film based cells. Donor densities are found to be in the range of 1Ol4 cmm3. Chemical etching improves the short-circuit current and fill factor and also results in Fermi level pinning of the photoanode, whereas photoelectrochemical etching improves the stability of the photoanode in polysulphide electrolyte.

CdS semiconductor films have been prepared from chemical bath deposition from basic solutions. Electron microscopic studies have revealed the presence of polycrystalline mixed cubic and hexagonal phases of CdS in the deposits. When surface treated, these layers show good photo electro chemical behaviour in Ti/CdS/$S/C cell configuration where as photo etching improves the stability of CdS photo anode in polysulphide electrolyte to a great extent. Optical absorption studies of these films have been carried out in the wavelength range 350-800 nm.

Polycrystalline "lms of CdTe and CdSe were electrodeposited onto titanium substrates from acidic baths, and, polycrystalline CdS thin "lms were prepared by chemical bath deposition method. Due to surface treatment these "lms show good photoelectrochemical behaviour in a polysulphide electrolyte with high conversion e$ciency and stability. The solid-state parameters of annealed "lms are calculated and compared with those of unannealed "lm-based cells. Chemical etching is found to improve short-circuit current and "ll-factor whereas photoelectrochemical etching technique improves the stability of photo-anode in polysulphide solution. Annealing promotes incipient fusion of small crystallites and thereby reduces the grain boundaries which are known to act as recombination centres for minority carriers and trapping centres for majority carriers. The conversion e$ciency and stability are found to improve by chemical etching of the semiconductor layer because chemical etching pins Fermi level of CdTe, CdSe and Cds photoanodes and promotes exchange current density.

A dual-band characteristic of stacked rectangular microstrip antenna is experimentally studied. It is a probe fed antenna for impedance matching with 50Ω coaxial cable. This antenna works well in the frequency range 2.86-4.63 GHz. It is basically a low cost, light weight medium gain antenna which is used for mobile communication. The variations of the length and width (1 mm) of the stacked rectangular patch antenna have been done. It is found to have dual resonance with increasing lower resonance frequency and almost constant upper resonance frequency with increases of the length and width of rectangular microstrip antenna. The input impedance and voltage standing wave ratio (VSWR) return loss have been measured with the help of network analyzer.

Microstrip antennas (MAS) are very useful antenna where low profile antennas are required. They are most popular due to their small size, low cost, light weight. The first aperture coupled microstrip antenna was introduced in 1985 by D M Pozar. Aperture coupled antenna is a particular antenna with high gain and wide bandwidth. This paper presents aperture coupled stacked patch antenna using air gap variation. The variation of air gap [2mm to 6mm] has been done between single patch antenna and an aperture coupled antenna. The main advantage of this antenna to increase the band width of the antenna as compared with single layered patch antenna. The resonant frequencies changes with air gap variations. The feed can be done either a conventional coaxial probe or through a coupling aperture in the ground plane as we done. This antenna works well in the frequency range (2.9 GHz to 6.0 GHz). The measured return loss exhibit an impedance bandwidth of 35%.The input impedance and VSWR return loss have been measured with the help of Network analyzer. [Agilent E8363B A.04.06] From the measured result it is found that the value of VSWR corresponding lower resonance frequencies increases from 14 to 2.2 with increasing air gap variation where as at the upper resonance frequencies is also increased from 1.8 to 2.3.

Organic electronics is currently experiencing a surge of activities worldwide prompted in part by recent advances in achieving high electronic mobility, light emission over a broad range of frequencies, demonstration of spin valve operation with giant magneto-resistance and other effects. Despite these encouraging promises, there are many roadblocks that hinder a broader proliferation of "plastic electronics" in contemporary technology. Such devices involve charge transport as a main process in their operation processes, and therefore, require high-performance charge-transporting materials. The charge-carrier mobility is the major determining factor for the speed of electronic devices. Arguably, the most significant of them is the challenge to achieve a comprehensive understanding of the fundamentals of charge injection and charge transport in organics. In spite of its simple definition, because of the difficulty of measuring velocity, accurate determination of the mobility of the carriers is not easy and indirect ways are used, each with its own advantages and disadvantages. The article discusses important mobility measurement techniques employed for organic optoelectronic devices.

Au, CI mixed phosphors were prepared in nitrogen atmosphere with various concentrations of impurities. Photoluminescence (PL) spectra were obtained. The peak of the PL spectrum shifts towards longer-wavelength values with increasing replacement of zinc by cadmium in the host lattice. The PL efficiency was found to decrease with increasing. CdS content whereas lattice constants increased with increasing CdS concentration.

When mechanically excited, initially the ML intensity increases, attains a maximum value and then decreases with time. The total M L intensity I r initially increases with the impact velocity V o of piston and attains a saturation value for higher values of V o and follows o and 1/ are constants. The ML intensity is the relation /.r=l°exp(-V/V o) where I T maximum for 20% CdS contents in the (Zn, Cd)S phosphors due to increase in hardness which may in turn increase the fracture stress and subsequently the piezoelectric field strength. The wavelength corresponding to the peak of both the ML and PL spectra shift towards longer wavelength with increasing CdS contents. Some models are discussed and it is concluded that the impulsive deformation of these phosphors may be due to piezoelectrification of newly created surfaces. The similarity of M L spectra with EL and PL spectra suggests that although the excitation processes are different, emission process is governed by the states of similar nature.

This paper presents air gap aperture coupled microstrip antenna for dual-band operation over the frequency range of (2.9 to 6.0 GHz). This antenna differs from any other microstrip antenna with their feeding structure of the radiating patch element. Input signal couples to the radiating patch trough the aperture that exists on the ground plane of microstrip feed line. The dual-band achieved by variation of air gap [2 mm to 6 mm] between single patch antenna and aperture coupled microstrip antenna. The main advantage of this type antenna is increased the bandwidth of the antenna as compared to a single layered patch antenna. The two resonant frequencies can vary over a wide frequency range and the input impedance is easily matched for both frequencies. The obtain ratios of resonance frequencies are variable from 2.1 GHz to 1.1 GHz with increasing the air gap between single patch and aperture coupled microstrip antenna. The measured return loss [-14 dB] exhibits an impedance bandwidth of 35%. The input impedance and VSWR return loss have been measured with the help of Network analyzer.