Photodetectors with ultrahigh sensitivity based on the composite made with all carbon-based materials consisting of graphite quantum dots (QDs), and two dimensional graphene crystal have been demonstrated. Under light illumination, remarkably, a photocurrent responsivity up to 4 × 107 AW−1 can be obtained. The underlying mechanism is attributed to the spatial separation of photogenerated electrons and holes due to the charge transfer caused by the appropriate band alignment across the interface between graphite QDs and graphene. Besides, the large absorptivity of graphite QDs and the excellent conductivity of the graphene sheet also play significant roles. Our result therefore demonstrates an outstanding illustration for the integration of the distinct properties of nanostructured carbon materials with different dimensionalities to achieve highly efficient devices. Together with the associated mechanism, it paves a valuable step for the further development of all carbon-based, cheap, and non-toxic optoelectronics devices with excellent performance.

We report the discovery of an enhancement of the random laser action in a nanocomposite comprising reduced graphene oxide nanoflakes and ZnO nanorods. We show that both emission intensity and lasing threshold exhibit an obvious improvement. Based on our theoretical calculations, the mechanism underlying the enhanced stimulated emission can be attributed to coupling between the optical transition and the surface plasmon resonance of the reduced graphene oxide nanoflakes, induced by the ZnO nanorod surface roughness. The approach we describe here will be very useful for the future development of high-efficiency optoelectronic devices and offers an alternative route for application of reduced graphene oxide.

Whispering-gallery-mode (WGM) resonance manipulated random laser action has been proposed. To illustrate our working principle, lasing characteristics of ZnO nanorods decorated with SiO2 nanospheres have been investigated. It is found that with the assistance of SiO2 nanospheres the emission spectrum exhibits a very narrow background signal with a few sharp lasing peaks and a very small full width at half-maximum of less than 0.3 nm. The differential quantum efficiency (ηd) of random laser action can be greatly enhanced by up to 735%. More interestingly, the wavelength of laser action of ZnO nanorods can be controlled by the decoration of different-size nanospheres. The underlying origin is attributed to the fact that the decorated nanospheres not only enable the generation of WGM resonance and enhance the peak emission intensity but also can serve as scattering centers. Cathodoluminescence mapping images of nanorods decorated with nanospheres and theoretical calculation based on the spherical cavity were utilized to confirm our proposed mechanism. These intriguing features manifest the tunability of mode-controlled random laser action by WGM resonance of nanospheres. Our discovery shown here may open up a new approach for the creation of highly efficient optoelectronic devices.

Based on the composite consisting of ZnO nanorods (NRs) grown on InGaN/GaN multiple quantum wells (MQWs), we have demonstrated a novel light-emitting device (LED) that has the capability to emit dual beam radiations. Interestingly, the relative intensity between the dual emissions is able to be manipulated by their polarizations. The underlying mechanism can be well understood in terms of the anisotropic optical properties arising from the geometric structures of constituent nanoscale materials. The results shown here may be extended to many other nanocomposite systems and pave a new pathway to create LEDs with tunable properties.

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