Kailasnath, M; John, P R; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier, 2008)
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Abstract:
This study was conducted to identify the concentration dependence of the operating wavelengths and the relative intensities in which a dye
mixture doped polymer optical fibre can operate. A comparative study of the radiative and Forster type energy transfer processes in Coumarin
540:Rhodamine 6G, Coumarin 540:Rhodamine B and Rhodamine 6G:Rhodamine B in methyl methacrylate (MMA) and poly(methyl methacrylate)
(PMMA) was done by fabricating a series of dye mixture doped polymer rods which have two emission peaks with varying relative intensities.
These rods can be used as preforms for the fabrication of polymer optical fibre amplifiers operating in the multi-wavelength regime. The 445 nm
line from an Nd:YAG pumped optical parametric oscillator (OPO) was used as the excitation source for the first two dye pairs and a frequency
doubled Nd:YAG laser emitting at 532 nm was used to excite the Rh 6G:Rh B pair. The fluorescence lifetimes of the donor molecule in pure
form as well as in the mixtures were experimentally measured in both monomer and polymer matrices by time-correlated single photon counting
technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was
analysed. It was found that radiative energy transfer mechanisms are more efficient in all the three dye pairs in liquid and solid matrices.
Kailasnath, M; Nishant, Kumar; Nampoori, V P N; Vallabhan, C P G; Radhakrishnan, P(Elsevier, 2008)
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Abstract:
Dependence of energy transfer parameters on excitation wavelength has been investigated in poly (methyl methacrylate) (PMMA) optical fibre preforms doped with C 540:Rh B dye mixture by studying the fluorescence intensity and the lifetime variations. A fluorescence spectrophotometer was used to record the excitation spectra of the samples for the emission wavelengths 495 and 580 nm. The fluorescence emission from the polymer rods was studied at four specific excitation wavelengths viz; 445, 465, 488 and 532 nm. The fluorescence lifetime of the donor molecule was experimentally measured in polymer matrix by time correlated single photon counting technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was analysed for three excitation wavelengths. It was found that any change in the excitation wavelength leads to significant variations in the quenching characteristics, which in turn affect the calculated energy transfer parameters.
Mohammed Yusuff, K K; Arun, Vasudevan; Robinson, P P; Manju, Sebastian; Leeju, P; Varsha, Gopalakrishnan; Digna, Vasudevan(Elsevier, Dyes and Pigments 82 (2009) 268–275, January 18, 2009)
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Abstract:
A novel bisazomethine Schiff base was synthesised by the condensation of 3-hydroxyquinoxaline-2-
carboxaldehyde and 2,3-diaminomaleonitrile. 1H NMR, 13C NMR, HPLC and FT-IR studies revealed that
the compound exists in two major tautomeric forms. The Schiff base exhibits positive absorption and
fluorescent solvatochromism and displays dual fluorescence with large stoke shifts. Cyclic voltammetric
analysis of the compound in 1:1 methanol–THF was influenced by scan rate. Thermal analysis of the
compound was undertaken using TG–DTA and DSC
Kumar, G A; Thomas, J; George, N; Nampoori, V P N; Radhakrishnan, P; Vallabhan, C P G(Society of Glass Technology, 2000)
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Abstract:
Optical absorption and emission spectral studies of free and metal naphthalocyanine doped borate glass matrix are reported for the first time. Absorption spectra recorded in the UV- VIS-NIR region show the characteristic absorption bands, namely, the B-band and Q-band of the naphthalocyanine (Nc) molecule. Some of the important spectral parameters, namely, the optical absorption coefficient (α), molar extinction coefficient (ε) and absorption cross section (σa) of the principal absorption transitions are determined. Optical band gap (Eg) of the materials evaluated from the functional dependence of absorption coefficient on photon energy lies in the range 1.6 eV≤Eg≤2.1 eV. All fluorescence spectra except that of EuNc consist of an intense band in the 765 nm region corresponding to the excitation of Q-band. In EuNc the maximum fluorescence intensity band is observed at 824 nm. The intensity of the principal fluorescence band is maximum in ZnNc, whereas it is minimum in H2Nc. Radiative parameters of the principal fluorescence transitions corresponding to the Q-band excitation are also reported for the naphthalocyanine and phthalocyanine based matrices.
V P N Nampoori; Mohammed Yusuff, K K; Arun,V; Mathew, S; Robinson, P P; Jose,M(Elsevier, Journal of Dyes and Pigments, March 20, 2010)
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Abstract:
The Schiff base, 3-hydroxyquinoxaline-2-carboxalidine-4-aminoantipyrine, was synthesized by the
condensation of 3-hydroxyquinoxaline-2-carboxaldehyde with 4-aminoantipyrine. HPLC, FT-IR and NMR
spectral data revealed that the compound exists predominantly in the amide tautomeric form and
exhibits both absorption and fluorescence solvatochromism, large stokes shift, two electron quasireversible
redox behaviour and good thermal stability, with a glass transition temperature of 104oC. The
third-order non-linear optical character was studied using open aperture Z-scan methodology employing
7 ns pulses at 532 nm. The third-order non-linear absorption coefficient, b, was 1.48 x 10-6 cm W-1 and
the imaginary part of the third-order non-linear optical susceptibility, Im c(3), was 3.36 x10-10 esu. The
optical limiting threshold for the compound was found to be 340 MW cm-2.
Mohammed Yusuff, K K; Nampoori, V P N; Arun,V; Mathew, S; Robinson, P P; Jose,M(Elsevier, Journal of Dyes and Pigments, March 20, 2010)
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Abstract:
The Schiff base, 3-hydroxyquinoxaline-2-carboxalidine-4-aminoantipyrine, was synthesized by the
condensation of 3-hydroxyquinoxaline-2-carboxaldehyde with 4-aminoantipyrine. HPLC, FT-IR and NMR
spectral data revealed that the compound exists predominantly in the amide tautomeric form and
exhibits both absorption and fluorescence solvatochromism, large stokes shift, two electron quasireversible
redox behaviour and good thermal stability, with a glass transition temperature of 104 oC. The
third-order non-linear optical character was studied using open aperture Z-scan methodology employing
7 ns pulses at 532 nm. The third-order non-linear absorption coefficient, b, was 1.48 x 10-6 cm W-1 and
the imaginary part of the third-order non-linear optical susceptibility, Im c(3), was 3.36x10-10 esu. The
optical limiting threshold for the compound was found to be 340 MW cm-2.