We demonstrate the working of organic-inorganic hybrid light emitting diodes using cadmium sulphide nanoparticles doped in light emitting polymers. Cadmium sulphide nanoparticles were prepared by precipitation technique and doped in active light emitting polymers. We used blue emitting polymer PFO and green emitting polymer F8BT as active polymers. The j-L-V curves of nanoparticles based devices were compared with polymer only standard devices. Our results show enhanced performance such as increased conductivity and higher luminance, when nanoparticle are incorporated into the device.
Biopolymer light emitting diodes were fabricated by using all solution processable polymers incorporating biomaterials such as deoxyribonucleic acid lipid complex as an electron blocking layer. Light emission is from a blend of fluorene based copolymers. The devices with electron blocking layer exhibited higher brightness and luminous efficiency. The increased luminance of the multilayer polymer LED is attributed to the contribution from DNA:CTMA as electron blocking layer and PFN, a derivative of polyfluorene, as electron injection layer. Our results show four fold increase in luminance values when DNA is used as electron blocking layer.
Deoxyribonucleic acid lipid complex thin films are used as a host material for laser dyes. We tested PicoGreen dye, which is commonly used for the quantification of single and double stranded DNA, for its applicability as lasing medium. PicoGreen dye exhibits enhanced fluorescence on intercalation with DNA. This enormous fluorescence emission is amplified in a planar microcavity to achieve yellow lasing. Here the role of DNA is not only a host medium, but also as a fluorescence dequencher. With the obtained results we have ample reasons to propose PicoGreen dye as a lasing medium, which can lead to the development of DNA based bio-lasers.
Chalcogenide glasses are amorphous semiconductors with a number of interesting properties required for photonic
devices. Particularly, their optical properties can be tuned through the change of the glass composition. We investigate
second-order nonlinear optical properties of chalcogenide glass (Ge27Se64Sb9) thin films fabricated by thermal
evaporation. The strong second-harmonic generation observed for the samples investigated is analyzed as a function of
incident polarization. Furthermore, the role of multipole effects in second-harmonic generation is also studied by using
two beams at the fundamental frequency. Our results suggest that the higher-multipole effects are present and contribute
significantly to the second-harmonic response of chalcogenide the samples.
We present the experimental investigations on the filament characteristics of sharply focused fs pulses (800 nm, 45 fs, 1
kHz) in air. Pulses with input powers in 3-12.2 P<sub>Cr</sub> range were focused using three different focusing geometries f/#10,
f/#15 and f/#20 corresponding to numerical apertures (NA) of 0.05, 0.033 and 0.025, respectively. The dynamics of
filaments were observed via direct imaging of the entire reaction zone. The length of the filament has decreased with
increasing NA from 0.025 to 0.05, while, the filament width has increased. For a given focusing geometry, the filament
length and width increased with increasing power. However with higher NA, the length and width were observed to
saturate at higher input powers. With the highest NA of 0.05 and higher input powers used in the current study, the
presence of coherently interacting multiple filaments either resulting in a fusion or exchange of power.
From the initial observation of self-channeling of high-peak power femtosecond (fs) laser pulses in air, propagation of
intense ultrashort laser pulses in different media has become one of the most investigated research areas. The
supercontinuum emission (SCE), a spectral manifestation of the spatio-temporal modifications experienced by a
propagating ultrashort laser pulse in a nonlinear medium, has many practical applications. However, the extent of blue
shift of SCE is reported to be constant due to the phenomenon of "intensity clamping". To further explore the recently
observed regime of filamentation without intensity clamping, we measured the evolution of spectral blue shift of SCE
resulting from the propagation of fs pulses (800 nm, 40 fs, 1 kHz) in distilled water under different focusing geometries.
The efficiency of SCE from tight focusing (f/6) geometry was always higher than the loose focusing (f/12) geometry for
both linear and circular polarized pulses. The blue edge of the SCE spectrum (λ<sub>min</sub>) was found to be blue shifted for f/6
focusing conditions compared to f/12 focusing geometry. The lower bound of the intensity deposited in the medium
measured from the self-emission from the filament demonstrated the existence of intensities ~ 6x10<sup>13</sup> Wcm<sup>-2</sup>, far beyond
the clamping intensities achieved erstwhile.
We present the design of a novel optical fiber sensor probe which can be used for measuring the critical mole fractions of
aqueous binary alcohol mixtures. The critical alcohol mole fractions we got are 0.3 for methanol and ethanol, 0.15 for 2-propanol and 0.05 and 0.1 for tert-butanol. The results obtained using the sensor probe also gives an evidence for
micellization in tert-butanol water mixtures.
An extrinsic fabry-perot interferometric pressure sensor is fabricated using a cavity formed by a metal diaphragm
and a single mode optical fiber. The compact sensor probe has been tested for static pressure response using
diaphragms of different metals.
In this article we present the bandgap engineering and spectral properties of ZnO-CdS and ZnO-TiO2 nanocomposites prepared by colloidal chemical synthesis. The optical bandgap (Eg) of the material is tunable between 2.62 and 4.12 eV. Emission peaks of ZnO-CdS change from 385 to 520 nm and those of ZnO-TiO2 change from 340 to 385 nm almost in proportion to the changes in Eg. It is possible to obtain a desired luminescence color from UV to green by simply adjusting the composition. ZnO-CdS and ZnO-TiO2 are potential nanocomposite materials for the tunable light emission.
Zinc Oxide nanoparticles and nanorods have been synthesized at an optimum temperature of 60°C using aqueous
solution of zinc acetate and potassium hydroxide in methanol. Particle and rod like structures were obtained by merely
varying the relative concentration of the reagents. A variety of techniques like UV-Vis absorption spectroscopy, X-ray
diffraction (XRD), photoluminescence, Fourier transform infrared (FTIR) spectroscopy and scanning electron
microscopy (SEM) were used to carry out structural and spectroscopic characterizations. FTIR confirms the preparation
of zinc oxide. XRD shows the formation of well crystalline nature and wurtzite structure of prepared zinc oxide samples.
Grain sizes were also calculated using XRD data and found to be in 11-15nm range for all preparations. Presence of one-dimensional
structures in the rod samples were confirmed by SEM images. Blue shift of the absorption peaks were found
due to quantum confinement of excitons. Capping action of polyvinyl pyrrolidone (PVP) was also studied. Use of PVP
leads to the decrement in aspect ratio of rods but provides spherical shaped nanostructures. Enhancement of UV-emission
intensity with suppression of green emission intensity was observed by the use of PVP during preparation.
Multimode laser emission is observed in a polymer optical fiber doped with a mixture of rhodamine 6G and rhodamine B dyes. Tuning of laser emission is achieved by using the mixture of dyes due to the energy transfer occurring from donor molecule (rhodamine 6G) to acceptor molecule (rhodamine B). The dye doped polymethylmethacrylate (PMMA) based polymer optical fiber is pumped axially at one end of the fiber using 532nm pulsed laser beam from an Nd: YAG laser and the fluorescence emission is collected from the other end. At low pump energy levels, fluorescence emission is observed. When the energy is increased beyond a threshold value, laser emission occurs with a multimode structure. The optical feedback for the gain medium is provided by the cylindrical surface of the optical fiber which acts as a cavity. This fact is confirmed by the mode spacing dependence on the diameter of the fiber.
The length-dependent tuning of the fluorescence spectra of a dye doped polymer fiber is reported. The fiber is pumped sideways and the fluorescence is measured from one of the ends. The excitation of a finite length of dye doped fiber is done by a diode pumped solid state laser at a wavelength of 532 nm. The fluorescence emission is measured at various positions of the fiber starting from a position closer to the pumping region and then progressing toward the other end of the fiber. We observe that the optical loss coefficients for shorter and longer distances of propagation through the dye doped fiber are different. At longer distances of propagation, a decrease in optical loss coefficient is observed. The fluorescence peaks exhibit a redshift of 12 nm from 589 to 610 nm as the point of illumination progresses toward the detector end. This is attributed to the self-absorption and re-emission of the laser dye in the fiber.