Rodrigues Joana, Medeiros Sloany, Vilarinho Paula M, Costa M Elisabete V, Monteiro Teresa
I3N & Physics Department, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
CICECO - Aveiro Institute of Materials, Department of Materials and Ceramics Engineering, University of Aveiro, 3810-193 Aveiro, Portugal.
Phys Chem Chem Phys. 2020 Apr 29;22(16):8572-8584. doi: 10.1039/d0cp00091d.
ZnO/ZnO2 composites grown by hydrothermal synthesis at low temperature (180 °C) and thermally annealed at 300 °C were fully analysed by morphological, structural and optical techniques. X-ray diffraction patterns (XRD) and Raman spectroscopy clearly evidence the presence of both crystalline phases in the ZnO/ZnO2 sample. The differential scanning calorimetry analysis and thermogravimetric profiles indicate an exothermic event with a peak temperature ca. 225 °C, which is accompanied by a 8.5% weight loss, being attributed to the crystallization of ZnO from ZnO2. Upon a thermal annealing treatment at 300 °C the ZnO2 phase was completely converted into ZnO, as measured by XRD and Raman spectroscopy. Photoluminescence investigations reveal that the emission is dominated by a broad band recombination in both samples, due to the overlapping of different emitting centres, and that the peak position of the PL emission is dependent on the excitation density. The ZnO/ZnO2 sample exhibits a widening of the bandgap when compared to the one only containing ZnO, likely related to the presence of the additional ZnO2 phase and suggesting a bandgap energy of ~3.42 eV for this compound. Surface analysis revealed that the sample exhibits a surface area of 90 m2 g-1, which decreases to 30 m2 g-1 after the thermal annealing and the full conversion into ZnO. This difference in the surface area showed particular relevance in the stability of the measured optical properties. Particularly, the intensity of the photoluminescence signal was seen to be higher in the ZnO/ZnO2 sample and strongly dependent on the measurement atmosphere, highlighting its potential to be employed in the fabrication of optical-based sensing systems for environmental applications, namely in gas sensors.
通过低温（180°C）水热合成并在300°C下进行热退火生长的ZnO/ZnO2复合材料，采用形态学、结构和光学技术进行了全面分析。X射线衍射图谱（XRD）和拉曼光谱清楚地证明了ZnO/ZnO2样品中两种晶相的存在。差示扫描量热分析和热重曲线表明存在一个放热事件，峰值温度约为225°C，同时伴有8.5%的重量损失，这归因于ZnO2结晶形成ZnO。通过XRD和拉曼光谱测量发现，在300°C进行热退火处理后，ZnO2相完全转变为ZnO。光致发光研究表明，由于不同发光中心的重叠，两个样品中的发射均以宽带复合为主，并且PL发射的峰值位置取决于激发密度。与仅含ZnO的样品相比，ZnO/ZnO2样品的带隙变宽，这可能与额外的ZnO2相的存在有关，表明该化合物的带隙能量约为3.42 eV。表面分析显示，该样品的表面积为90 m2 g-1，热退火并完全转变为ZnO后降至30 m2 g-1。表面积的这种差异在测量的光学性质的稳定性方面表现出特别的相关性。特别是，ZnO/ZnO2样品中的光致发光信号强度更高，并且强烈依赖于测量气氛，突出了其在基于光学的环境应用传感系统（即气体传感器）制造中的应用潜力。
