Photophysics of soret-excited tin(IV) porphyrins in solution.

The photophysics of low-chlorin tin(IV) tetraphenylporphyrin dihydroxide, a core building block for axially substituted supramolecular tin porphyrin constructs, has been studied in a variety of hydrogen-bonding, nonpolar, and aprotic polar solvents using steady-state, nanosecond, and femtosecond time-resolved emission, and femtosecond time-resolved absorption methods. In hydrogen-bonding solvents the metalloporphyrin exists as solvated monomers, and its Soret-excited S2 state in these solvents exhibits the expected linear energy gap law relationship with first-order population decay times in the 0.8 to 1.7 ps range. Evidence is presented that this metalloporphyrin aggregates in other solvents at the concentrations typically used for these ultrafast measurements and yields species-averaged time-resolved data. Cw laser excitation in the Q-band under deaerated conditions produces weak S2-S0 fluorescence (photon upconversion) as a result of triplet-triplet annihilation.

Controlled synthesis, characterization, and application of iron oxide nanoparticles for oral delivery of insulin.

Impurity-free, controlled synthesis of iron oxide nanoparticle, in ultrapure water and chitosan, using laser ablation technique and its application for type II diabetes management through oral delivery of insulin-loaded iron oxide-chitosan nanocomposite is presented. The purity of the nanoparticle is monitored by laser-induced breakdown spectroscopy technique. The synthesized iron oxide nanoparticle was characterized by UV/Vis absorption spectroscopy, and morphological study was performed by scanning electron microscope. The intensity of absorption peak and wavelength corresponding to peak of the nanoparticle prepared in water and chitosan is dependent on the laser energy used for ablation purpose. Red shift in the absorption peak wavelength was observed by increasing laser energy. In addition to red shift, an increase in intensity of absorption peak was also seen when ablating laser energy was increased. The appearance of a weak peak around 295 nm was observed in iron oxide-chitosan nanocomposite. The spherical shape of the nanoparticle synthesized at the lower laser energy has gradually changed to triangular and irregular shaped structures as ablating laser energy was increased. The spherical nanoparticles loaded with insulin were used for oral delivery for diabetic management. The iron oxide-chitosan nanocomposite loaded with insulin has resulted in reduction in blood glucose level in mild diabetic, subdiabetic, and severely diabetic rats; more than 51 % reduction in blood glucose level, compared to the control group, has been achieved in the present work.

Upconversion based tunable white-light generation in Ln:Y(2)O(3) nanocrystalline phosphor (Ln = Tm/Er/Yb).

We report the generation of efficient white light based on upconversion (UC) in Tm(3+)/Er(3+)/Yb(3+):Y(2)O(3) nanocrystalline phosphor synthesized by simple and cost effective solution combustion technique on 976 nm laser excitation. The calculated color coordinates (using 1931 CIE standard) for samples annealed at different temperatures vary from (0.16, 0.30) to (0.32, 0.33) with dopant concentration, annealing temperature and the pump power; thus providing a wide color tunability including the white one. White emission is observed even at a very low laser power (60 mW). The maximum upconversion efficiency obtained for white emission is 2.79% with the color coordinates (0.30, 0.32) at laser power of 420 mW which is quite close to the standard white color coordinates.

Judd-Ofelt analysis of Tm and energy transfer studies between Tm and Er codoped in lithium tellurite network.

Optical properties of Tm(3+) and Er(3+) and Tm(3+)+Er(3+) codoped tellurite glass have been studied using different wavelengths from a Ti-Sapphire laser as excitation source. The energy transfer from one rare earth to other on excitation with different wavelengths has been studied. The Judd-Ofelt theory has been used to calculate various optical parameters suitable for laser oscillation.

Intense green and red upconversion emissions from Ho(3+) in presence of Yb(3+) in Li:TeO2 glass.

Weak visible emission is observed at 545 nm and 660 nm on 976 nm excitation of Ho(3+) ions doped in tellurite glass. Addition of ytterbium to the doped glass causes a large increase in intensity of the green and the red emissions. In addition to these two new emissions of Ho(3+) one in the blue and the other in the NIR region are also observed. This increase in intensity is ascribed to energy transfer from ytterbium ions to holmium ions. Rate equation model has been proposed to study the upconversion emission and its dependence on pumping power. Possible upconversion mechanisms for these emissions are also discussed. Effect of changing the concentration of Yb(3+) on the emission intensity, lifetime and full width at half maximum (FWHM) in (5)F(4)((5)S(2)) --> (5)I(8) transition of Ho(3+) in codoped sample has also been studied.