Photoinduced Formation of Peroxide Ions on La2O3 and Nd2O3 under O-2: Effects of Excitation Wavelength and Crystal Structure

摘要

Photoinduced formation of peroxide ions on La2O3 and Nd2O3 under O-2 was studied by in-situ microprobe Raman spectroscopy with attention focused on the effect of excitation wavelength and crystal structure on the O-2(2-) formation. It was found that photoexcitations at 633, 532, 514, and 325 nm can induce O-2(2-) formation over La2O3 at 450 degrees C. By contrast, photoexcitation at 785 nm does not cause formation of O-2(2-) up to 500 degrees C. Photoexcitation at 325 nm can induce O-2(2-) formation on cubic Nd2O3 at 25 degrees C, but cannot induce O-2(2-) formation on hexagonal Nd2O3 up to 200 degrees C. The significant difference in the behavior of O-2(2-) formation over the Nd2O3 samples of the two structures can be related to the difference in the capacity to adsorb O-2. Since the number of oxygen vacancies in cubic Nd2O3 is larger than that in the hexagonal one, the former has a higher capacity than the latter to adsorb O-2. As a result, cubic Nd2O3 is more favorable to the reaction of O-2 with O2- to generate O-2(2-). The structural similarity between cubic Nd2O3 and Nd2O2(O-2) may be another factor in favor of peroxide formation.