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Hydrothermal-sintering Preparation of Cr2+:ZnSe/ZnSe Nanotwins with Core-shell Structure
Tingting ZHANG, Fangyuan WANG, Changyou LIU, Guorong ZHANG, Jiahui LÜ, Yuchen SONG, Wanqi JIE
J Inorg Mat ›› 2024, Vol. 39 ›› Issue (4) : 409-415.
PDF(5889 KB)
PDF(5889 KB)
Hydrothermal-sintering Preparation of Cr2+:ZnSe/ZnSe Nanotwins with Core-shell Structure
Cr2+ doped ZnSe nanocrystals are an important type of mid-infrared materials. ZnSe-based semiconductor nanocrystals with core-shell structure have shown excellent optical, electrical and catalytic properties. The defects of nanocrystals are one of the important factors affecting their properties. For example, nanocrystals with twinned structure have higher strength and hardness. In order to improve the comprehensive performance of doped nanocrystals, Cr2+:ZnSe/ZnSe nanocrystals with core-shell structure were prepared by two-step hydrothermal processes, using soluble Zn salt as Zn source, newly prepared NaHSe solution as Se source, and Cr(AC)2 as doping source, and chemically stable nanocrystals at room temperature were obtained by sintering at 400 and 800 ℃ under protection of argon or high vacuum, respectively. Their structural and morphological characterization results show that the nanocrystalline size is mainly concentrated in the range of 20-30 nm, the shell thickness is about 2.6 nm, and the nanocrystals have delamination defects, thus twins are developed. The analysis results show that the twin plane is (111), the angle between the adjacent two crystal planes is 70.02°± 0.5°. The twin density of the sample increases with the increase of the crystallinity, which indicates that release of lattice distortion energy leads to formation of delamination and twin. Meanwhile, the twin growth can be explained by dislocation induced nucleation-growth. XPS analysis shows that Cr elements with a valence of +2 exist in the nanocrystals, and the reflection spectroscopy test shows that nanocrystals have an absorption band around 1775 nm, indicating that the prepared nanocrystals with twins have a promising mid-infrared luminescent property.
Cr2+:ZnSe / core-shell structure / nanotwins / twinning mechanism / sintering
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In the recent two decades, Cr2+:ZnSe crystals have been widely used as a gain media for 2∼3 μm mid-infrared lasers. However, it still remains a huge challenge for researchers to meet more and more requirements on the crystals with high qualities and large sizes. In this work, one Cr2+:ZnSe single crystal with a diameter of about 15 mm was successfully grown by chemical vapor transporting (CVT) with NH4Cl in a closed quartz ampoule without any seed. The transmission of as-grown crystal is up to 70% in the UV-VIS-NIR region and is with an intense characteristic absorption of Cr2+ near 1770 nm. The X-ray photoelectron spectroscopy (XPS) shows that the incorporation of chlorine anions does not significantly affect the valence distribution of components in the crystal. The mid-infrared photoluminescence spectra show a strong and broad emission band centered at 2400 nm with a width of 600 nm under the 1770 nm laser excitation at room temperature. The calculated cross sections of absorption and emission were 1.31×10−18 and 1.4×10−18 cm2, respectively. The measured photoluminescence decay time was about 6.9 μs at room temperature. It is confirmed that the method of CVT with NH4Cl is suitable for the growth of Cr2+:ZnSe single crystals, which are expected to have a promising prospect in mid-infrared laser applications in further.
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感谢西北工业大学-南洋理工大学研究生交流项目的资助。感谢南洋理工大学于霆老师团队的帮助。
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