Abstract In this report, nanoparticles (NPs) of zinc oxide (ZnO) were synthesized through auto-combustion route and annealed in air at different temperatures: 200, 400, 600 and 800 °C. The single phase nature has been confirmed via X-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis. The average of crystallite sizes increased progressively as the thermal annealing increase and ranging between 13.8 and 39.7 nm. Raman spectra resembled to that of hexagonal ZnO wurtzite structure, the narrowing in E2H (438 cm−1) Raman phonon mode in sequence with further annealing indicates improvement in the crystallinity and reduction in the local atomic defects of oxygen vacancy (Vo2+). The defects create energy deep bands within the band gap region and diminish the UV emission efficiency that has been assessed through photoluminescence (PL) spectroscopic. The donor band of oxygen vacancy (Vo2+) was ∼ 1 eV above valence band (VB), whereas the acceptor band of zinc vacancy (VZn2−) was at ∼ 0.85 eV above the VB. The ZnO NPs that was annealed at lowest temperature of 200 °C exhibited different behavior trend in which the UV-PL band was diminished clearly, blue shifted to lower wave length and appeared as small plateau at the range of 380–270 nm corresponding to high band gap energy (3.8–4.6 eV), which is indicative to low crystal quality and presence of clusters. We used density function theory (DFT) calculation for computing the HOMO-LUMO band gap of supposed clusters ZnnOn (n = 2, 3, 5, 10). The high band gap energy of the simulated clusters was agreed with that of ZnO NPs annealed at 200 °C that gives indirect evidence on the formation of clusters.

中文翻译：

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退火对 ZnO 纳米粒子结构和光学特性的影响，并通过 DFT 计算追踪簇的形成

摘要 在本报告中，氧化锌 (ZnO) 纳米粒子 (NPs) 通过自燃路线合成，并在不同温度下在空气中退火：200、400、600 和 800 °C。单相性质已通过 X 射线衍射 (XRD) 和选区电子衍射 (SAED) 分析得到证实。随着热退火的增加，晶粒尺寸的平均值逐渐增加，范围在 13.8 和 39.7 nm 之间。拉曼光谱类似于六方 ZnO 纤锌矿结构，随着进一步退火，E2H (438 cm-1) 拉曼声子模式的变窄表明结晶度的提高和氧空位 (Vo2+) 的局部原子缺陷的减少。这些缺陷会在带隙区域内产生能量深带，并降低通过光致发光 (PL) 光谱评估的紫外线发射效率。氧空位 (Vo2+) 的供体带比价带 (VB) 高约 1 eV，而锌空位的受主带 (VZn2-) 比价带高约 0.85 eV。在 200 °C 的最低温度下退火的 ZnO NPs 表现出不同的行为趋势，其中 UV-PL 带明显减弱，蓝移到较低波长并在 380-270 nm 范围内出现小平台，对应于高带隙能量（3.8-4.6 eV），这表明低晶体质量和簇的存在。我们使用密度函数理论 (DFT) 计算来计算假设簇 ZnnOn (n = 2, 3, 5, 10) 的 HOMO-LUMO 带隙。