Dual amplified spontaneous emission as evidence for superexciplex from the dye LD473

Pulsed laser excitation of certain laser dye solutions prepares the sample molecules in a condition, unavailable under steady state lamp excitation. Excited molecules in large concentration obtainable under intense pulse laser pumping appear to undergo superexciplex interaction in which two excited molecules form an association with a solvent molecule acting as a link. This paper shows some of the important features of such superexciplexes with LD473 dye molecule as a reference.     

Photodynamic damage study of HeLa cell line using ALA

The present study evaluates the photodynamic damage with 5-aminolevulinic acid (5-ALA) using HeLa as experimental model. HeLa cell line was irradiated with red light (He-Ne laser, λ = 632.8 CW nm). The influence of different incubation times and concentrations of 5-ALA, different irradiation doses and various combinations of photosensitizer and light doses on the cellular viability of HeLa cells were studied. The optimal uptake of photosensitizer ALA in HeLa cells was investigated by means of PpIX fluorescence intensity by exciting the HeLa cell suspension at 450 nm and a detection wavelength set at 690 nm. Cells viability was determined by means of trypan blue solution. The spectrometric measurements showed that the maximal cellular uptake of 5-ALA occurred after 4 h in vitro incubation. We found that the combination with 5-ALA and laser irradiation leads to time/concentration-dependent increase of cells death and also energy doses-dependent enlarge the cells death. The fluorescence intensity after PDD of carcinoma cells reduce when compared with the control group. The fluorescence emission spectral profiles after PDD of carcinoma cells showed a dip around 425–525 nm when compared with the control group. This may be due to the damage of mitochondria component of cells. The percentage of HeLa cells after PDD shows that the percentage of cells survival rate as function of laser dose (power). Hence it is clear that at 200 μg/ml ALA and 20 mW laser irradiation, more than 70% of HeLa cells were dead after 15 min.     

Influences of Co doping on the structural and optical properties of ZnO nanostructured

Pure and Co-doped ZnO nanostructured samples have been synthesized by a chemical route. We have studied the structural and optical properties of the samples by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), field-emission transmission electron microscope (FETEM), energy-dispersive X-ray (EDX) analysis and UV–VIS spectroscopy. The XRD patterns show that all the samples are hexagonal wurtzite structures. Changes in crystallite size due to mechanical activation were also determined from X-ray measurements. These results were correlated with changes in particle size followed by SEM and TEM. The average crystallite sizes obtained from XRD were between 20 to 25 nm. The TEM images showed the average particle size of undoped ZnO nanostructure was about 20 nm whereas the smallest average grain size at 3% Co was about 15 nm. Optical parameters such as absorption coefficient (α), energy band gap (E _g ), the refractive index (n), and dielectric constants (σ) have been determined using different methods.     

Fluorescence spectra of cultured normal and malignant lung cells

Fluorescence Spectroscopy has emerged as a new modality to characterize physicochemical properties of biomolecules. The biomolecules have certain photophysical properties based on their molecular structure and these properties have been considered as useful parameters to monitor alterations in the functional, morphological and micro environmental changes in the cells and tissues. In this study the fluorescence emission spectra of normal and malignant lung cells were recorded for different excitation wavelengths: 230, 300, 340, and 450 nm, corresponding to the absorption of tyrosine, tryptophan, collagen or elastin, Nicotinamide adenine dinucleotide (NADH) and flavin adeno dinucleotide (FAD). Similarly excitation spectra were also recorded at 340 nm. The emission profiles showed considerable difference between the malignant and normal cells with the malignant cells having more fluorescence intensity than that of normal cells keeping emission at 340 nm. Our study had shown the discriminating features between normal and carcinoma cells lines because of higher concentration of tryptophan (1.5 times), NADH (3 times), and flavin (4 times) in carcinoma cell lines.     

Improved performance of silicon‐nanoparticle film‐coated dye‐sensitized solar cells

Silicon (Si) nanoparticles with average size of 13 nm and orange–red luminescence under UV absorption were synthesized using electrochemical etching of silicon wafers. A film of Si nanoparticles with thickness of 0.75 µm to 2.6 µm was coated on the glass (TiO₂ side) of a dye‐sensitized solar cell (DSSC). The cell exhibited nearly 9% enhancement in power conversion efficiency (η) at film thickness of ～2.4 µm under solar irradiation of 100 mW/cm² (AM 1.5) with improved fill factor and short‐circuit current density. This study revealed for the first time that the Si‐nanoparticle film converting UV into visible light and helping in homogeneous irradiation, can be utilized for improving the efficiency of the DSSCs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photodynamic damage (PDD) study using stimulated raman scattering

In the current study, photodynamic damage in different cell cultures was examined using a pulsed laser light. Two different experiments were performed to analyse the photodynamic damage. For the first one, a stimulated Raman scattering laser has been obtained by exciting DMSO liquid with Nd-YAG laser, second harmonic generation, 532 nm. The resulted SRS wavelength is pulsed 630 nm. 1 ml ALA (200 μg/ml) was added to cell suspension and keep it for incubated for 4 h then irradiate the suspension with SRS wavelength 630 nm at different light dose 8, 12, 17, 25, 30, 40, 60, 100, 150, 200 μJ for 10 pluses and obtain the cell degradation. We repeat the step above but for 30 pluses. Finally for the second experiment, 1 ml ALA (200 μg/ml) was added to cell suspension and was incubated for 4 h and then irradiated with Nd-YAG Laser at wavelength 532 nm. Different doses range between 8 up to 200 μJ for 10 pluses only and the cell degradation rate was measured.     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.     

Structural and solvent dependence of superexciplex

In this paper, we show that a few coumarin dye solutions exhibit dual amplified spontaneous emission (ASE) spectra under pulsed laser excitation, though all these solutions exhibit only one fluorescence band under steady-state conditions. The anomalous band, appearing only in ASE spectra, had been attributed to the superexciplex--a new molecular species. This is made of two excited molecules and is obtainable only under pulsed laser excitation. This complex is different from the well known excimer or exciplex, wherein only one atom or molecule is in the excited state. The superexciplex is possible with the two polar excited molecules coming together to form an excited state association, with the solvent acting as some sort of bridge. With very polar dye molecules, such an association is possible even with the inert benzene acting as a bridge; otherwise solvents like ethyl acetate, with an oxygen atom, is necessary for the linkage.