Viscosity dependence of the rotational reorientation of coumarins by depolarization technique

Steady-​state and time-​resolved fluorescence behavior of coumarin 6 (C6) and coumarin 7 (C7) in alkane and alc. solvents has been investigated. Steady-​state absorption and emission spectral behavior of C6 and C7 was found not to be affected by both the solvents. Time-​resolved fluorescence anisotropy measurements showed that the rotational reorientation of the probe became faster in alc. A comparison of the exptl. measured rotational reorientation times of C6 and C7 were identical in a given solvent at a particular temp. The present study has been undertaken to examine the role of friction experienced by the polar solutes in a polar and non-​polar solvents. Mol. shape and size were similar but the friction experienced by these probes in n-​tridecane and n-​propanol solvents viscosities were varied by temp. However, it was obsd. that C6 and C7 rotates faster in alc. than alkane and the obsd. results were discussed in the last section

One Pot Room Temperature Synthesis of CTAB Capped Highly Luminescent CdTe Quantum Dots in an Aqueous Medium and their Free Radical Scavenging Activity

In the present paper, we have reported room temperature synthesis of CTAB capped CdTe quantum dots in an aqueous medium for free radical scavenging assay choosing BHA as the reference free radical. The formation of CdTe QDs required relatively shorter reaction time with quantum yield up to 40 %. Their optical properties, surface morphology and structural characterizations were employed through UV-Visible absorption spectroscopy, Photoluminescence, FE-SEM, Powder-XRD, Raman spectroscopy and DSC-TGA techniques. These QDs showed maximum absorption at 551 nm and their shape was spherical with average particle size of about 3-4 nm as noted by surface morphology. The results showed that the synthesized CdTe QDs have an excellent antioxidant activity. This type of semiconductor quantum dot is a promising material for the upcoming generation in high speed optics and biomedical fields

Temperature-dependent reorientation dynamics of laser dyes in alkane and alcohol solvents

The rotational dynamics of similar sized coumarin 6 (C6), coumarin 7 (C7), and coumarin 30 (C30) laser dyes has been studied in alkane and alcohol solvents using steady-state and time-resolved fluorescence depolarization methods. The estimated rotational reorientation times of these probes are observed to vary linearly as a function of viscosity over the range of temperatures studied. It is found that the rotational reorientation time measurements of these molecules in alcohol and alkane typically have relaxation times on the order of picoseconds. The rotational reorientation times of the C7 molecule are greater than those of the C6 and C30 molecules. It was observed that C7 rotates faster in both the solvents than C6 and C30, indicating that the effects of the medium and structural differences of molecules lead to slower rotation. © Published by NRC Research Press

Fiber Bragg Granting Sensor for Detection of Nitrate Concentration in Water

The concentrations of chemical species in drinking water are of great interest. We demonstrated etched fiber Bragg grating (FBG) as a concentration sensor for nitrate by analyzing the Bragg wavelength shift with concentration of chemical solution. The FBG is fabricated by phase mask technique on single mode Ge-B co-doped photosensitive fiber. Sensitivity of FBGs to the surrounding solution concentration can be enhanced by reducing diameter of the cladding with 40 % HF solution. The maximum sensitivity achieved is 1.322 10-3 nm/ppm. The overall shift of Bragg wavelength is of the order of 6.611 10-2 nm for 10 to 50 ppm concentration. Copyright © 2011 IFSA