estimates the population relaxation rate. However, this remains under investigation.The AT splitting and gain without inversion in the Mollow absorption spectrum imply that the absorption and gain inside a single QD are tunable. In the AT configuration, the absorption of the probe beam can be switched on and off by applying a strong optical field. In contrast, in the MAS experiment, the absorption of the frequency fixed probe beam can be tuned to be positive or negative (gain) by adjusting the pump field strength. Our results are the first step toward the realization of electromagnetically induced transparency and lasing without inversion in the spinbased lambda system and suggest that QDs offer the potential to be used as elements in optoelectronics and quantum logic devices (4, 27).Note added in proof: Since the submission of this paper, two papers have appeared on http://arxiv.org that report studies of the resonant excitation of quantum dots in the strong excitation regime. The first (31) reports a measurement of the fluorescence correlation function that Mollow first calculated, and the second (32) reports Rabi oscillations.References and Notes 1. D. Loss, D. P. DiVincenzo, Phys. Rev. A. 57, 120 (1998 Materials emitting light in the deep ultraviolet region around 200 nanometers are essential in a widerange of applications, such as information storage technology, environmental protection, and medical treatment. Hexagonal boron nitride (hBN), which was recently found to be a promising deep ultraviolet light emitter, has traditionally been synthesized under high pressure and at high temperature. We successfully synthesized high-purity hBN crystals at atmospheric pressure by using a nickelmolybdenum solvent. The obtained hBN crystals emitted intense 215-nanometer luminescence at room temperature. This study demonstrates an easier way to grow high-quality hBN crystals, through their liquid-phase deposition on a substrate at atmospheric pressure.H exagonal boron nitride (hBN) and cubic boron nitride (cBN) are known as the representative crystal structures of BN. hBN is chemically and thermally stable and has been widely used as an electrical insulator and heat-resistant material for several decades; cBN, which is a high-density phase, is almost as hard as diamond (1).Promising semiconductor characteristics due to a direct band gap of 5.97 eV were recently discovered in high-purity hBN crystals obtained by a high-pressure flux method, paving the way for a material that efficiently emits deep ultraviolet (DUV) light (2, 3). Similar to aluminum nitride (AlN) (4) and gallium nitride (GaN) (5), hBN may have attractive potential as a wide-band gap material. The layered structure of hBN makes the material mechanically weak, but it has greater chemical and thermal stability than GaN and AlN. The interesting optical properties of hBN, such as its huge exciton-binding energy (2), are due to its anisotropic structure, whereas a single crystal's basal plane in hBN is not easily broken because of its strong in-plane bonds. T...

Luminescence D 6540 Deep Ultraviolet Light-Emitting Hexagonal Boron Nitride Synthesized at Atmospheric Pressure. -High-purity hexagonal BN crystals are prepared at atmospheric pressure from hexagonal BN powder using Ni metal or Ni-Mo alloy as solvent (1350-1500°C, 12 h). The samples are characterized by optical microscopy, SEM, Raman spectroscopy, powder XRD, and cathodoluminescence spectroscopy. By addition of Mo to the Ni solvent, the yield of recrystallized BN crystals is substantially increased. The obtained hexagonal BN crystals emit intense 215 nm luminescence at room temperature. Materials emitting light in the region around 200 nm are essential for applications such as information storage technology, environmental protection, and medical treatment. -(KUBOTA*, Y.; WATANABE, K.; TSUDA, O.; TANIGUCHI, T.; Sci. (Washington, D. C., USA) 317 (2007) 5840, 932-934; Natl. Inst. Mater. Sci., Tsukuba, Ibaraki 305, Japan; Eng.) -W. Pewestorf 45-012

Hexagonal boron nitride (hBN), with a layered structure similar to that of graphite, is the simplest III-V nitride compound. High-purity hBN emits intense 215-nm bandedge luminescence, which is attributed to free excitons and which may have potential wide band gap semiconductor characteristics. 1 It is a promising material for the production of deep ultraviolet light-emitting devices. However, the synthesis routes for high-purity hBN single crystal have thus far all been high-pressure, high-temperature (HP-HT) ones. [1][2][3] Since products of HP-HT synthesis are generally limited in size, development of an alternative synthesis process that can fabricate hBN fine crystal on a large scale is an important step in realizing hBN's potential.We recently found a new way of obtaining hBN crystals at atmospheric pressure using Ni-Mo alloy as a solvent. 4 The obtained crystals exhibit the band-edge optical nature of deep ultraviolet luminescence at 215 nm at room temperature, which indicates high crystallinity of our crystals.

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