ZnO@mesoporous silica nanocomposite was prepared by the impregnation of a CMI-1 material in a Zn(NO 3 ) 2 solution followed by calcination under O 2 . Intensive characterization was carried out by N 2 adsorption-desorption measurements, scanning and transmission electron microscopy. The optical properties of the ZnO@mesoporous silica nanocomposite were studied by photoluminescence spectroscopy. Quantum Size Effect was firstly demonstrated by subjecting the sample to a 254 nm excitation light, and was further confirmed by using a 680 nm excitation laser beam, which implies a two-photon absorption process. By focusing the 680 nm laser beam on different places in the sample, a very localized random laser effect, also induced by a two-photon absorption process, was detected.

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Abstract. Alloys of silicon (Si), germanium (Ge) and tin (Sn) are continuously attracting research attention as possible direct band gap semiconductors with prospective applications in optoelectronics. The direct gap property may be brought about by the alloy composition alone or combined with the influence of strain, when an alloy layer is grown on a virtual substrate of different composition. In search for direct gap materials, the electronic structure of relaxed or strained Ge

Abstract:In this letter, we propose a heterostructure design for tunnel field effect transistors with two low direct bandgap group IV compounds, GeSn and highly tensely strained Ge in combination with ternary SiGeSn alloy. Electronic band calculations show that strained Ge, used as channel, grown on Ge 1-x Sn x (x>9%) buffer, as source, becomes a direct bandgap which significantly increases the tunneling probability. The SiGeSn ternaries are well suitable as drain since they offer a large indirect bandgap. The growth of such heterostructures with the desired band alignment is presented. The crystalline quality of the (Si)Ge(Sn) layers is similar to state-of-the-art SiGe layers.

Abstract:The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser. References and links 1. B. Hu and M. Nuss, "Imaging with terahertz waves," Opt. Lett. 20, 1716Lett. 20, -1718Lett. 20, (1995 36, 2587-2589 (2011). 29. S. Donati, "Developing self-mixing interferometry for instrumentation and measurements," Laser Photon. Rev. 6, 393-417 (2012