RESUMEN
Phosphor materials with broad spectral range and an average emission lifetime (20â µs) have been achieved from carbon dots (CDs)-NaCl crystals. A one-pot synthesis pathway has been developed for CDs-NaCl crystals formation at room temperature. Precursor for CDs materials was screened at room temperature by oxidation methodology from different simple sugar molecules. CDs (size less than 10â nm) prepared from the fructose sugar exhibit most intense emission. Utilizing ripe banana peel (contains â¼27% of fructose) as a precursor for the carbon dot formation, white-light emission with a CIE index of (0.29, 0.34) has been achieved from the single source with CDs-NaCl crystals upon excitation at 430â nm. The crystals also function as Fabry-Perot (F-P) mode resonator for lasing, with a laser threshold value of 0.9â mW and a resonating Q-factor of 207. These results outline a new approach for realizing F-P lasing and white light emission from a non-toxic green source with a quick, facile and low-cost synthesis procedure.
RESUMEN
We have investigated the roles of structural modification and polar effects in the optical nonlinearities of a series of selectively mixed ß-pyrrole functionalized tetraphenylporphyrin, MTPP(CHO)(R)2 (R = H, Br, 2-thienyl, phenyl (Ph), phenylethynyl (PE) compounds and their metal (Cu(II), Zn(II)) complexes in toluene. In the present study, we have used phase conjugation geometry of the four wave mixing process to measure the third order nonlinear susceptibility (χ(3)) and the second order hyperpolarizabilty ((γ)) with picosecond laser pulse excitation at 532 nm. An increase in the values of χ(3) and (γ) for electron-withdrawing groups was observed whereas an opposite trend was noticed for the electron-donating groups at the ß-pyrrole positions. In the Cu(II) and Zn(II) complexes of substituted free base porphyrins, the distortion of the macrocyclic ring may be responsible for the reduction of the values of χ(3) and (γ). From fluorescence measurements, it has been found that the electron-donating and electron-withdrawing substituted groups at ß-pyrrole positions and also the macrocyclic ring distortion of the porphyrin lead to increased radiationless transitions.
RESUMEN
The migration and diffusion modulated excitation energy transfer has been studied in a new dye pair 7-diethylamino-4-methylcoumarin (donor) to 3,3'-dimethyloxacarbocyanine iodide (acceptor) by steady-state and picosecond time-resolved spectroscopy. To reduce the artifact of self-absorption, at high donor concentrations, the time-resolved studies have been carried out in thin films of polyvinyl alcohol (solid matrix) and in methanol (liquid phase) at front-face geometry of excitation. The Forster-type (nonradiative) energy transfer [Discuss. Faraday Soc. 27, 7 (1959)] takes place directly from donor to acceptor in case of solid matrix, while Yokota-Tanimoto model [J. Phys. Soc. Jpn. 22, 779 (1967)] for diffusion has been found to be operating in the liquid phase. It has been found here that the high interaction strength between donor and acceptor molecules as compared to that among donors masks the effect of energy migration and diffusion at high donor concentrations. The rate and efficiency of energy transfer increase with increasing the acceptor concentration. This has been confirmed by the study of acceptor kinetics.