Single-crystalline fibers have distinct structures and optical properties comparing with the bulk crystals. In this article, two types of single-crystalline fibers of deuterated potassium dihydrogen phosphate (K(H1−x
DKDP) are obtained by rapid growth in room-temperature supersaturated solution. X-ray diffraction analysis reveals that these DKDP single-crystalline fibers belong to tetragonal (I
-42d) and monoclinic (P
/c) phases, respectively. The crystal structure of the tetragonal DKDP single-crystalline fiber is identical to that of the bulk DKDP tetragonal crystal reported. The lattice parameters of the monoclinic DKDP fiber (with the deuterium content of 55%) are a = 14.6571 Å, b = 4.5187 Å, c = 18.6962 Å, and β = 108.030°, which is a new crystal phase of DKDP. The monoclinic DKDP single-crystalline fiber is metastable at the present experimental condition and readily transit to the corresponding DKDP tetragonal phase in solution and in solid by grinding. The optical experiment shows that the highly deuterated tetragonal DKDP single-crystalline fiber possesses excellent optical guided-wave and effective second-harmonic generation properties. DKDP single-crystalline fibers are expected to be the suitable candidates for fabrication of the miniaturized nonlinear optical devices.
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