Graphene sheets that are now routinely obtained by the exfoliation/reduction of graphite oxide exhibit Raman spectra unlike traditional graphene systems. The general attributes of the Raman spectra of these ‘wrinkled graphene’ are first reaffirmed by evaluating the spectra of samples prepared by seven different exfoliation-reduction methods. These graphene sheets exhibit highly broadened D and G Raman bands and in addition, have a modulated bump in place of the conventional 2D (G′) band. It is shown that the high wavenumber ‘bump’ can be resolved into the conventional 2D band and several defect activated peaks such as G*, D+D′ and 2D′. The broad G band could also be deconvoluted into the actual G band and the D′ band, thereby attributing the broadening in the G band to the presence of this defect activated band. Two additional modes, named as D* at 1190 cm-1 and D** at ∼1500 cm-1 could be identified. These peculiar features in the Raman spectrum of ‘graphene’ are attributed to the highly disordered and wrinkled (defective) morphology of the sheets. The affect of defects are further augmented due to the finite crystallite size of these graphene sheets. The dispersion in the band positions and peak intensities with respect to the laser energy are also demonstrated

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Herein, we report the fabrication of hydrogen gas sensors based on noble nanometal decorated one dimensional multi walled carbon nanotubes and two dimensional graphene by a simple drop casting technique, with practical applications in view. Pt decorated functionalized graphene sheets (Pt/f-G) and Pt decorated functionalized multi walled carbon nanotubes (Pt/f-MWNT) were synthesized and employed as hydrogen sensors. Systematic investigation of hydrogen sensing, at a low detection level of 4 vol% hydrogen in air, of (Pt/f-G) reveals a response time comparable to that of (Pt/f-MWNT) but with a two fold increase in the sensitivity at room temperature. These sensors were also found to be stable over repeated cycles of hydrogenation and dehydrogenation.

Luminescent solar concentrators (LSCs) offer significant potential for solar energy capture in the urban environment. Here, the first example of a planar, doped LSC using Lumogen Red (LR305) as the luminophore and a di‐ureasil organic–inorganic hybrid as the waveguide is reported. The di‐ureasil waveguide offers several advantages over organic polymer waveguides including facile solution‐processing from benign solvents and extension of the absorption window through energy transfer. Spectral evaluation using absorption and photoluminescence spectroscopies is used to optimize the LSC composition, yielding optical efficiencies as high as 14.5% (300–800 nm). A power conversion efficiency (PCE) of 0.54% is obtained for the champion LSC coupled to a c‐Si PV cell using the di‐ureasil precursor as an optical glue to minimize interfacial losses. Finally, a simple figure of merit to evaluate the performance of LSC‐solar cell composite systems is proposed that enables comparison of the actual improvement in the efficiency of solar cells due to the attachment of the LSC, irrespective of the LSC design, architecture or materials. A PCE of 17.4% for the solar cell in the emission region of the LSC is obtained, which is a remarkable improvement of ≈40% over its AM 1.5G value.

In the present work, we have systematically investigated the effect of different exfoliation conditions on the synthesis of graphene from graphite oxide (GO). Four different conditions were used to exfoliate GO: Ar @ 1050 °C, vacuum @ 200 °C, H2 + Ar mixture @ 200 °C, and H2 @ 200 °C. Few layered graphenes obtained by these methods were characterized by thermogravimetry, diffractometry, spectroscopy, microscopy, surface, and elemental analysis techniques. New insights obtained upon a detailed analysis of these are presented. Although the morphology and characteristics of these graphenes are similar, differences are observed in the amount of functional groups present, resulting in considerable change in their electrical properties. These results show conclusively that the atmosphere for exfoliation of GO plays a critical role in low temperature syntheses of graphene. It is observed that exfoliation-reduction of GO in pure hydrogen atmosphere at 200 °C results in the highest quality of a few layered graphene sheets.