Hexagonal CdTe nanoparticles with hexagonal phase are chemically prepared. Transmission electron microscopic analysis shows that the prepared nanoparticles are hexagonal in shape. Again, in the selected-area electron diffraction pattern, ring-shaped identical patterns containing sharp bright spots are observed, which confirm that nanoparticles are polycrystalline in nature. The observed X-ray diffraction (XRD) peaks on matching with the standard data confirm the formation of hexagonal phase. Again, from the observed absorption peak at 449 nm, the bandgap is calculated as 2.4 eV using Tauc's equation, which is found to be slightly higher compared with the reported bandgap of cubic CdTe nanoparticles. Further, Urbach energy is found as 534 meV, which indicates the presence of defect states in the nanoparticles, and the refractive index of synthesized nanoparticles is calculated as 2.6. Rietveld refinement of X-ray data is performed for the determination of lattice structural parameters, which is then used for the computation of density functional theory (DFT)-based bandgap using Quantum ESPRESSO code. Finally, the bandgap obtained from the theoretical study and experimental study is compared. The innovation herein lies in the use of experimental XRD data for bandgap calculation using DFT.

中文翻译：

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具有六方相的合成六方 CdTe 纳米粒子的光学性质：密度泛函理论支持的带隙和态密度计算

化学制备具有六方相的六方 CdTe 纳米颗粒。透射电镜分析表明，所制备的纳米粒子呈六角形。同样，在选定区域的电子衍射图案中，观察到包含尖锐亮点的环形相同图案，这证实纳米粒子本质上是多晶的。与标准数据匹配时观察到的 X 射线衍射 (XRD) 峰证实了六方相的形成。同样，根据在 449 nm 处观察到的吸收峰，使用 Tauc 方程将带隙计算为 2.4 eV，发现与报道的立方 CdTe 纳米粒子带隙相比略高。此外，发现 Urbach 能量为 534 meV，这表明纳米粒子中存在缺陷态，计算得到合成纳米粒子的折射率为2.6。对 X 射线数据进行 Rietveld 细化以确定晶格结构参数，然后使用 Quantum ESPRESSO 代码将其用于计算基于密度泛函理论 (DFT) 的带隙。最后，比较了理论研究和实验研究得到的带隙。本文的创新在于使用实验 XRD 数据使用 DFT 计算带隙。