Spectral and nonlinear optical characteristics of nanocomposites of ZnO–Ag

In this Letter we present the spectral and nonlinear optical properties of ZnO–Ag nanocomposites prepared by colloidal chemical synthesis. Obvious enhancement of ultraviolet (UV) emission of the samples is observed and the strongest UV emission is over three times than that of pure ZnO. These nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behaviour which increases with increasing Ag volume fraction. The observed nonlinear absorption is explained through two photon absorption followed by free carrier absorption. ZnO–Ag is a potential nanocomposite material for the UV light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.

Effect of self assembly on the nonlinear optical characteristics of ZnO thin films

In the present work, we report the third order nonlinear optical properties of ZnO thin films deposited using self assembly, sol gel process as well as pulsed laser ablation by z scan technique. ZnO thin films clearly exhibit a negative nonlinear index of refraction at 532 nm and the observed nonlinear refraction is attributed to two photon absorption followed by free carrier absorption. Although the absolute nonlinear values for these films are comparable, there is a change in the sign of the absorptive nonlinearity of the films. The films developed by dip coating and pulsed laser ablation exhibit reverse saturable absorption whereas the self assembled film exhibits saturable absorption. These different nonlinear characteristics in the self assembled films can be mainly attributed to the saturation of linear absorption of the ZnO defect states.

Linear and nonlinear optical characteristics of ZnO-SiO2 nanocomposites.

We present the spectral and nonlinear optical properties of ZnO-SiO2 nanocomposites prepared by colloidal chemical synthesis. Obvious enhancement of ultraviolet (UV) emission of the samples is observed, and the strongest UV emission of a typical ZnO-SiO2 nanocomposite is over three times stronger than that of pure ZnO. The nonlinearity of the silica colloid is low, and its nonlinear response can be improved by making composites with ZnO. These nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behavior. The observed nonlinear absorption is explained through two photon absorption followed by weak free carrier absorption and nonlinear scattering. The nonlinear refractive index and the nonlinear absorption increase with increasing ZnO volume fraction and can be attributed to the enhancement of exciton oscillator strength. ZnO-SiO2 is a potential nanocomposite material for the UV light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.

Modification of spectral characteristics and optogalvanic response in neon hollow cathode under laser excitation

The changes in emission characteristics of a neon hollow cathode discharge by resonant laser excitation of 1s 5→2p 2 and 1s 5→2p 4 transition have been studied by simultaneously monitoring the optogalvanic effect and the laser induced fluorescence. It has been observed that resonant excitation causes substantial variation in the relative intensities of lines in the emission spectrum of neon discharge.

On the luminescence characteristics of cerium and copper doped barium sulphide phosphor

Photoluminescence, thermoluminescence and phosphorescence studies of cerium and copper doped BaS phosphors are attempted. Cu+ centres in BaS lattice activate red emission while Ce3+ sensitize the blue emission. Results are explained on the basis of superposition theory involving monomolecular kinetics. In Randall and Wilkins model, the decay and TL studies are found to corelate each other.

Fluorescence Decay Characteristics of the Green Emission From CaF2:Ho3+

Variations in the decay times of the characteristic green emissions at 522.7, 551.3, 549.6, 547.6, 542.2, 540.2, 535.9 and 533.5nm from CaF2 :H03+ with concentration are studied at RT and LNT. A pulsed N2 laser beam of power density 1.5 MW cm-2 is used for the excitation. Temperature dependent concentration quenching of the decay times are observed for all the emission bands. But an increase in the decay time due to the reabsorption process is also observed for a few of the above bands.

Excitation and Emission Characteristics of Pretreated SrS:Mn:Ce Phosphors

Excitation and emission spectra of SrS : Mn : Ce phosphors have been studied in detail at various Mn and Ce concentrations. In order to study the effect of external pressure on phosphors, the samples were pretreated under various pressures. Four bands around 470 nm, 530 nm, 310 nm and 620 nm were observed, when the samples were excited with 265 nm radiation. The effect of pressure is to reduce the fluorescence ability of the phosphors, and the luminescence vanishes above O· 1 ton m-2 pressure. The fluorescence ability, however, can be regained on retiring the sample. The emission mechanism has been attributed to two luminescentcenters in the forbidden gap. An appreciable amount of photocurrent has also been observed for the sample.

Ultra-wideband slot antenna with band-notch characteristics for wireless USB dongle applications

A compact ultra-wideband (UWB) printed slot antenna is described, suitable for integration with the printed circuit board (PCB) of a wireless, universal, serial-bus dongle. The design comprises of a near-rectangular slot fed by a coplanar waveguide (CPW) printed on a PCB of size 20 × 30 mm2. It has a large bandwidth covering the 3.1–10.6 GHz UWB band, with omnidirectional radiation patterns. Further, a notched band centered at 5.45 GHz wireless local area network bands is obtained within the wide bandwidth by inserting a narrow slot inside the tuning stub. Details of the antenna design are described, and the experimental results of the constructed prototype are presented. The time domain studies on the antenna shows a linear phase response throughout the band except at the notched frequency. The transient analysis of the antenna indicates very little pulse distortion confirming its suitability for high speed wireless connectivity.

Studies on ASE, Lasing and NLO characteristics in Certain Laser Dyes

Observing the wide possibilities of fluorescent dyes, an exhaustive investigation is done in laser dyes mainly focusing on Coumarin 540 which has a very strong emission in the green region. The photophysics of the dye is studied in detail in a good number of solvent environments. The results of the amplified spontaneous emission and lasing behaviour in both dye solution and different polymer solid state matrices and the ptotostability of the these matrices are investigated using the photoacoustic technique and the same are also included in this thesis. The energy transfer behaviour in dye mixtures which could be utilized for laser studies and bio-analysis are also presented. The nonlinear characterization of Coumarin540 forms the last part of the experimental investigations presented in the thesis.