Banerjee Dhritiman, Banerjee Payal, Kar Asit Kumar
Micro and Nano Science Laboratory, Department of Physics, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, 826004, India.
Department of Chemistry, National Tsing Hua University, Hsinchu, 300044, Taiwan.
Phys Chem Chem Phys. 2022 Jan 26;24(4):2424-2440. doi: 10.1039/d1cp05110e.
The effects of surface modification on the defect state densities, optical properties, and photocatalytic and quantum efficiencies of zinc oxide (ZnO) nanoplates were studied in this work. The aim of this study is to identify the photophysical processes that dictate the quenching of emission from defect states upon surface modification and the role of different defects such as zinc interstitials (Zn) or oxygen vacancies (V) beside the photophysical processes in determining the photocatalytic efficiency of plate-like ZnO nanostructures. For controlling the intrinsic defect state densities of ZnO nanoplates, which is difficult to achieve, their surface was modified using different polymers such as PMMA and PVA. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) emission spectroscopy were employed to identify and quantify the defect states. The analysis of relative defect state densities of Zn or V showed that Zn significantly impacts the photocatalytic activity (PCA) besides V, but it has a lower influence than V because of the difference in the accessibility and intrinsic nature of these two defects. Synchronous quenching of emission from different defect states with different formation energies and its correlation with the photocatalytic activity led us to conclude that photophysical processes such as concentration-dependent Förster resonance energy transfer (FRET), charge transfer (CT) and Zn defects play a significant role behind PCA, which has been previously reported to be influenced by V only. FRET and CT also play a critical role behind emission quenching upon surface modification. Upon the surface modification of nanoplates, a drop in the quantum efficiency from 12.14% to 4.44% was observed with the fine-tuning of emission colour from bluish-white to blue. Besides the defect states, FRET and CT phenomena are dominant in reducing the quantum efficiency of hybrid light-emitting diodes (HyLEDs) and photocatalytic efficiency. Therefore, the work outlines the reason behind the suppression of luminescence and photocatalytic efficiency of ZnO nanoparticles after surface modification and how to optimise them for their applications as an emissive layer in HyLEDs and efficient photocatalysts.
本工作研究了表面改性对氧化锌（ZnO）纳米片的缺陷态密度、光学性质、光催化和量子效率的影响。本研究的目的是确定在表面改性时决定缺陷态发射猝灭的光物理过程，以及除光物理过程外不同缺陷（如锌间隙（Zn）或氧空位（V））在决定片状ZnO纳米结构光催化效率方面的作用。为了控制难以实现的ZnO纳米片的本征缺陷态密度，使用不同的聚合物（如PMMA和PVA）对其表面进行改性。采用X射线光电子能谱（XPS）和光致发光（PL）发射光谱来识别和量化缺陷态。对Zn或V的相对缺陷态密度分析表明，除V外，Zn对光催化活性（PCA）也有显著影响，但由于这两种缺陷的可及性和本征性质不同，其影响比V小。不同形成能的不同缺陷态发射的同步猝灭及其与光催化活性的相关性使我们得出结论，浓度依赖的Förster共振能量转移（FRET）、电荷转移（CT）和Zn缺陷等光物理过程在PCA背后起重要作用，此前报道PCA仅受V影响。FRET和CT在表面改性时发射猝灭背后也起关键作用。在纳米片表面改性后，随着发射颜色从蓝白色微调至蓝色，量子效率从12.14%降至4.44%。除缺陷态外，FRET和CT现象在降低混合发光二极管（HyLEDs）的量子效率和光催化效率方面占主导地位。因此，这项工作概述了表面改性后ZnO纳米颗粒发光和光催化效率受到抑制的原因，以及如何对其进行优化，使其作为HyLEDs的发光层和高效光催化剂应用。
