Ultraviolet light emission at a wavelength of 250 nm was observed from Be-doped single crystals of cubic boron nitride (cBN) grown at high pressure and high temperatures. We found that dopants of Be were localized in the grown crystals when a small amount of Be was added to the crystals. The crystals had boundaries of blue-colored Be-rich regions and amber-colored ones. These colored regions were divided by the boundaries of growth sectors. When a direct current was induced across the boundaries, UV light emission was clearly observed. The crystals may include self-organized p–n regions along the growth sectors. Although some crystalline imperfections still prevent the crystals from exhibiting properties of materials that can emit UV light with a wide band gap (6.3 eV), it is noticeable that bulk single crystals have been synthesized that contain self-organized p–n boundaries and show UV light emission.

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