Room-temperature excitonic emission with a phonon replica from graphene nanosheets deposited on Ni-nanocrystallites/Si-nanoporous pillar array.

Graphene nanosheets (GNSs) were grown on a Si nanoporous pillar array (Si-NPA) via chemical vapour deposition, using a thin layer of pre-deposited Ni nanocrystallites as catalyst. GNSs were determined to be of high quality and good dispersivity, with a typical diameter size of 15 × 8 nm. Light absorption measurements showed that GNSs had an absorption band edge at 3.3 eV. They also showed sharp and regular excitonic emitting peaks in the ultraviolet and visible region (2.06-3.6 eV). Moreover, phonon replicas with long-term stability appeared with the excitonic peaks at room temperature. Temperature-dependent photoluminescence from the GNSs revealed that the excitonic emission derived from free and bound excitonic recombination. A physical model based on band energy theory was constructed to analyse the carrier transport of GNSs. The Ni nanocrystallites on Si-NPA, which acted as a metal-enhanced fluorescence substrate, were supposed to accelerate the excitonic recombination of GNSs and enhanced the measured emission intensity. Results of this study would be valuable in determining the luminescence mechanism of GNSs and could be applied in real-world optoelectronic devices.

Thiolate-assisted cation exchange reaction for the synthesis of near-infrared photoluminescent Hg(x)Cd(1-x)Te nanocrystals.

In this paper, we report the synthesis of dot- and branch-shaped Hg(x)Cd(1-x)Te nanocrystals (NCs) with good stability and a high quantum yield of about 30% through an elaborate cation exchange reaction at room temperature. The large red-shifts in both absorption spectra and photoluminescence (PL) spectra confirmed the substitution of mercury ions for cadmium ions and the formation of Hg(x)Cd(1-x)Te NCs. Interesting periodical XRD peaks observed in as-obtained Hg(x)Cd(1-x)Te NCs indicated the formation of layered metal thiolates, which not only played a key role in introducing mercury ions during the cation exchange process, but also acted as ligands to maintain the emission stability of newly formed Hg(x)Cd(1-x)Te NCs. The results indicate that the red-shift in PL emission has close-correlation with several parameters (such as the amounts of thiols and mercury ions, the sample store time, etc.).