Study for d-electronic states in titanium dioxide by doping of transition metal and control of oxygen defects

用化学输运反应法生长了单晶体。为了控制氧空位的产生，通过光谱和X射线衍射的测量，确定了氧或氢气氛下热处理的实验条件，并对生长态、氢离子注入、氧或氢气氛下退火的单晶进行了光吸收谱和ESR谱的测量。氧退火后晶体的颜色由生长时的浅蓝色变为黄色，最后变为无色。氢退火使无色晶体还原为深蓝色晶体。在氧气气氛下反复热处理，它再次变成深绿色，黄色和无色。由于晶体的颜色差异对应于缺陷状态的颜色差异，因此建立了控制缺陷状态的方法。光学吸收和ESR谱是相同的生长，氢热处理和H离子注入样品。用以Ti为中心的d电子的存在很好地解释了所得到的[001]方向的各向异性g张量。大小2×2×2mm^3，透明，呈紫色或深蓝色。它们的基本吸收边比未掺杂的晶体位于低能侧。掺铌单晶在2.5eV以下的低能区有较强的吸收，其吸收光谱与未掺铌单晶氢退火后的吸收光谱相似。这表明它们在电子结构上的相似性。

Single-crystals of anatase form were grown by means of chemical transport reaction method. For the control of oxygen vacancies, the measurements of spectra and X-ray diffraction were performed to establish the experimental condition for heat-treatments under the oxygen or hydrogen atmosphere.Optical absorption and ESR spectra were measured for anatase single crystals as-grown, implanted by H ions, annealed under oxygen or hydrogen atmosphere at desired temperature. The color of the crystal changed from pale-blue (as-grown) through yellow to colorless ones on oxygen annealing. The colorless crystal was reduced to dark-blue one by hydrogen annealing. On repetitive heat treatment under oxygen atmosphere, it becomes dark-green, yellow and colorless, again. Since the difference in color of the crystal corresponds to that in the state of defects, it was established to control the defect states. Optical absorption and ESR spectra were same for the as-grown, hydrogen-heat-treated and H ion implanted samples. The obtained anisotropic g tensor to [001] direction is well interpreted by the presence of the delectrons centered at Ti.V-or Nb-doped anatase single crystals were successfully synthesized by the use of rutile form solid solution as raw material. They were 2×2×2mm^3 in size and transparent with purple or dark-blue color, respectively. The fundamental absorption edges of them were located at lower energy side than undoped crystal. The Nb-doped single crystal has strong absorption in lower energy region from 2.5 eV.The absorption spectrum of the Nb-doped single crystal resembles to that of undoped crystal with hydrogen annealing. This indicates the similarity in electronic structure each other.