Chloroform is available as not only an organic solvent but also photochemical molecular storage for synthetically important chemicals such as Cl(2), HCl, and COCl(2). We have succeeded in synthesizing organochlorine compounds, hydrochloric salt of amines, ureas, organic carbonates, and polycarbonate in practical high yields with photodecomposed chloroform.
Since the seminal observation of room-temperature laser emission from ZnO thin films and nanowires, numerous attempts have been carried out for detailed understanding of the lasing mechanism in ZnO. In spite of the extensive efforts performed over the last decades, the origin of optical gain at room temperature is still a matter of considerable discussion , .We show that ZnO microcrystals with a size of a few micrometers exhibit purely excitonic lasing at room temperature without showing any symptoms of electron-hole plasma emission. We then present the distinct experimental evidence that the room-temperature
Structure
and properties of Li-doped MgO have been extensively
studied during the past decades in view of the effect of aliovalent
doping on the catalytic, optical absorption and magnetic properties.
However, the photoluminescence (PL) properties of Li-doped MgO have
not been systematically investigated previously. In this work, we
prepared micrometer-sized Li-doped MgO crystals using solid-phase
redox reaction between B2O3 and metals of Mg
and Li under argon atmosphere. The resulting Li-doped MgO microcrystals
exhibit blue (2.8 eV or 440 nm) and orange PL (2.1 eV or 580 nm) emissions
under excitation with photons of energies of ∼5 and ∼3
eV, respectively. The blue PL is attributed to the bulk oxygen vacancies,
or F-type centers, whose emission energy levels are
modified by the Li ions incorporated into the MgO structure. On the
other hand, the orange PL presumably results from the oxygen vacancies
at the near surface regions where a substantial bandgap narrowing
down to visible range of ∼3 eV occurs. It is also found that
the photoexcited electrons generated by surface interband transition
can be transferred to the surface emission states via thermal activation,
resulting in temperature antiquenching of the orange PL emission.
Hence, the present method provides a simple and effective way to prepare
visible luminescent Li-doped MgO microcrystals with an intriguing
effect of aliovalent doping both on the bulk and surface electronic
structures.
Research on semiconductor nanowires underlies the development of the miniaturization of laser devices with low cost and low energy consumption. In general, nanowire lasers are made of direct band gap semiconductors, e.g., GaN, ZnO and CdS, and their band-edge emissions are used to achieve optically pumped laser emission. In addition to the existing class of nanowire lasers, we here show that air-annealed micrometer-sized MgO cubic crystals with well-defined facets exhibit room-temperature stimulated emission at 394 nm under pulsed laser pumping at ∼350 nm. Surface midgap states are assumed to be responsible for the excitation and emission processes. The present findings will not only provide opportunities for the development of miniaturized lasers composed of insulating oxides, but will also open up functionality in various families of cubic crystalline materials.
We investigate the interaction between superconductivity and defect-induced d0 ferromagnetism using a composite consisting of MgB2 and MgO nanocrystals. The composite exhibits a ferromagnetic hysteresis behavior in the temperature region from 40 to 300 K. Defective MgO nanocrystals (∼20 nm) embedded in the composite are considered to be responsible for the observed ferromagnetism. The zero field cool and field cool magnetization curves show that the superconducting transition occurs at Tc = 38.6 K, in agreement with Tc of pure MgB2. In the temperature region from Tc to 0.9Tc (∼35 K), the magnetization hysteresis curves show a superposition of ferromagnetic (F) and superconducting (S) signals. When the temperature of the system is decreased below 0.65Tc (∼25 K), the S signals dominate over the F signals. The resulting magnetic hysteresis loops are highly asymmetric and the descending filed branch is nearly flat, as predicted in the case of surface pinning. At temperatures below 0.5Tc (∼20 K), a sharp peak is developed near zero field in the magnetization hysteresis curves, implying an enhancement of superconducting vortex pinning. The observed pinning enhancement most likely results from magnetic pinning due to randomly distributed magnetic MgO grains, which yield the magnetic inhomogeneity and the related pinning potential in a length scale of ∼100 nm. Thus, the present ferromagnetic/superconducting composite provides an ideal model system that demonstrates the availability of d0 ferromagnetism as a source of magnetic potential for effective vortex pinning.
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