Anatase TiO₂ is an efficient water splitting photocatalyst using UV light, but solar energy harvesting requires the presence of midgap states to increase visible light absorption. Despite numerous studies, important questions remain regarding the photophysics in O vacancy doped TiO₂. By employing extreme ultraviolet reflection–absorption (XUV-RA) spectroscopy at the Ti M_2,3-edge, spectral signatures of both large and small polaron states are identified, allowing ultrafast electron and hole dynamics in these states to be independently resolved. Results show that visible light absorption occurs via promotion of an electron from the small polaron state to the TiO₂ conduction band. In contrast, absorption of UV light results in direct band gap excitation followed by carrier relaxation during which hot holes trap as small polarons in 45 ± 42 fs, and hot electrons couple to polar optical phonons leading to vibrational coherence and large polaron formation in 945 ± 92 fs.

中文翻译：

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锐钛矿 TiO2 中的可见光吸收和热载流子俘获：表面氧空位的作用

锐钛矿 TiO ₂是一种使用紫外光的高效水分解光催化剂，但太阳能收集需要存在中间间隙状态以增加可见光吸收。_{尽管进行了大量研究，但关于 O 空位掺杂 TiO 2}中的光物理学的重要问题仍然存在。_{通过在 Ti M 2,3}边缘采用极紫外反射 - 吸收 (XUV-RA) 光谱，可以识别大小极化子态的光谱特征，从而独立解析这些状态下的超快电子和空穴动力学。结果表明，可见光的吸收是通过将电子从小极化子态促进到 TiO _{2来实现的。}导带。相比之下，紫外光的吸收导致直接带隙激发，随后载流子弛豫，在此期间热空穴在 45 ± 42 fs 中捕获为小极化子，热电子与极性光学声子耦合，导致振动相干性和在 945 ± 中形成大极化子92飞秒。