Functionalized gold nanoparticles as phosphorescent nanomaterials and sensors

Ligand-capped gold nanoparticles were synthesized by capping monothiol derivatives of 2,2'-dipyridyl onto the surface of Au nanoparticles (Au-BT). The average size of the metal core is around 4 nm, with a shell of ~340 bipyridine ligands around the Au nanoparticle. The high local concentration of the chelating ligands (~5 M) around the Au nanoparticle makes these particles excellent ion sponges, and their complexation with EuIII/TbIII ions yields phosphorescent nanomaterials. Absorption spectral studies confirm a 1:3 complexation between EuIII/TbIII ions and bipyridines, functionalized on the surface of Au nanoparticles. The red-emitting Au-BT:EuIII complex exhibits a long lifetime of 0.36 ms with six line-like emission peaks, whereas the green-emitting Au-BT:TbIII complex exhibits a lifetime of 0.7 ms with four line-like emission peaks. These phosphorescent nanomaterials, designed by linking BT:EuIII complexes to Au nanoparticles, were further utilized as sensors for metal cations. A dramatic decrease in the luminescence was observed upon addition of alkaline earth metal ions (Ca2+, Mg2+) and transition metal ions (Cu2+, Zn2+, Ni2+), resulting from an isomorphous substitution of EuIII ions, whereas the luminescence intensity was not influenced by the addition of Na+ and K+ ions. Direct interaction of bipyridine-capped Au nanoparticles with Cu2+ ions brings the nanohybrid systems closer, leading to the formation of three-dimensional superstructures. Strong interparticle plasmon interactions were observed in these closely spaced Au nanoparticles

Modulating FRET in Organic–Inorganic Nanohybrids for Light Harvesting Applications

The energy transfer efficiencies of organic–inorganic nanohybrids comprised of two structurally similar squaraine dyes and CdSe nanoparticles were studied in detail and compared. Carbazole based unsymmetrical squaraine dyes (CTSQ-1 and CTSQ-2) having modified absorption characteristics were considered for modulating the effect of the overlap integral on energy transfer rate with the designed QDs. CTSQ-2 with ∼1.75 times higher molar extinction coefficient and 35 nm red-shift in absorption resulted in an ∼2.4 times faster energy transfer rate with QD. The calculated energy transfer rates (<i>k</i>_T = 1.35 × 10⁸ s^–1 and 3.26 × 10⁸ s^–1 respectively for QD:CTSQ-1 and QD:CTSQ-2 nanohybrids) are at least one order of magnitude higher than both radiative (<i>k</i>_r = 5.97 × 10⁶ s^–1) and nonradiative decay rate constants (<i>k</i>_nr = 1.89 × 10⁷ s^–1) of QDs yielding very high FRET efficiency. The Stern–Volmer analysis of the quenching data indicated mainly static interaction of dyes with the QDs thus suggesting formation of organic–inorganic nanohybrids. When incorporated in dye-sensitized solar cells, the nanohybrids with 93% FRET efficiency, exhibited an overall 43% improvement in the photovoltaic performance. Among the two architectures employed for device fabrication the one with the smallest donor–acceptor distance delivered the best performance. Due to increased contribution from QDs, the IPCE spectra clearly indicate panchromatic response from the visible to NIR region. Thus, photovoltaic performance of NIR absorbing dyes were successfully improved by constructing panchromatic organic–inorganic nanohybrid materials

Revealing charge carrier dynamics in squaraine:[6, 6]-phenyl-C 71-butyric acid methyl ester based organic solar cells

Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM71) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM71 in SQ results in the formation of polaron pairs with ∼550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM71 compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC71 molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM71 but also gives the facts relating to the effect of PCBM71 mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex recombinations in the blend. These findings have been complimented by the charge transport study in the device using impedance spectroscopy. The various important transport parameters are transit time (τt), diffusion constant (Dn), global mobility (μ) and carrier lifetime (τr). The values of these parameters are 26.38 μs, 4.64x10-6 cm2s-1, 6.12x10-6 cm2V-1s-1 and 399 μs, respectively. To the best of our knowledge such study related to SQ is not present in the literature comprehensively

Revealing charge carrier dynamics in squaraine: [6,6]-phenyl-C 71-butyric acid methyl ester based organic solar cells

Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM71) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM71 in SQ results in the formation of polaron pairs with similar to 550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM71 compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC71 molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM71 but also gives the facts relating to the effect of PCBM71 mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex recombinations in the blend. These findings have been complimented by the charge transport study in the device using impedance spectroscopy. The various important transport parameters are transit time (tau(t)), diffusion constant (D-n), global mobility (mu) and carrier lifetime (tau(r)). The values of these parameters are 26.38 mu s, 4.64x10(-6) cm(2)s(-1), 6.12x10(-6) cm(2)V(-1)s(-1) and 399 mu s, respectively. To the best of our knowledge such study related to SQ is not present in the literature comprehensively