Berger T, Sterrer M, Diwald O, Knözinger E, Panayotov D, Thompson T L, Yates J T
Institut für Materialchemie, Technical University of Vienna, A-1210 Vienna, Austria.
J Phys Chem B. 2005 Apr 7;109(13):6061-8. doi: 10.1021/jp0404293.
Ultraviolet light-induced electron-hole pair excitations in anatase TiO(2) powders were studied by a combination of electron paramagnetic resonance and infrared spectroscopy measurements. During continuous UV irradiation in the mW.cm(-2) range, photogenerated electrons are either trapped at localized sites, giving paramagnetic Ti(3+) centers, or remain in the conduction band as EPR silent species which may be observed by their IR absorption. Using low temperatures (90 K) to reduce the rate of the electron-hole recombination processes, trapped electrons and conduction band electrons exhibit lifetimes of hours. The EPR-detected holes produced by photoexcitation are O(-) species, produced from lattice O(2-) ions. It is found that under high vacuum conditions, the major fraction of photoexcited electrons remains in the conduction band. At 298 K, all stable hole and electron states are lost from TiO(2). Defect sites produced by oxygen removal during annealing of anatase TiO(2) are found to produce a Ti(3+) EPR spectrum identical to that of trapped electrons, which originate from photoexcitation of oxidized TiO(2). Efficient electron scavenging by adsorbed O(2) at 140 K is found to produce two long-lived O(2)(-) surface species associated with different cation surface sites. Reduced TiO(2), produced by annealing in vacuum, has been shown to be less efficient in hole trapping than oxidized TiO(2).
通过电子顺磁共振和红外光谱测量相结合的方法，研究了锐钛矿型TiO₂粉末中紫外线诱导的电子 - 空穴对激发。在毫瓦·厘米⁻²范围内的连续紫外照射过程中，光生电子要么被捕获在局域位置，产生顺磁性的Ti³⁺中心，要么作为EPR沉默物种留在导带中，可通过其红外吸收观察到。使用低温（90 K）来降低电子 - 空穴复合过程的速率，捕获电子和导带电子的寿命可达数小时。光激发产生的EPR检测到的空穴是由晶格O²⁻离子产生的O⁻物种。发现在高真空条件下，大部分光激发电子留在导带中。在298 K时，TiO₂中所有稳定的空穴和电子态都消失了。发现在锐钛矿型TiO₂退火过程中因氧去除而产生的缺陷位点会产生与捕获电子相同的Ti³⁺ EPR谱，捕获电子源于氧化TiO₂的光激发。发现在140 K时，吸附的O₂对电子的有效清除会产生与不同阳离子表面位点相关的两种长寿命O₂⁻表面物种。已表明在真空中退火产生的还原TiO₂在空穴捕获方面不如氧化TiO₂有效。
