Photoinduced Formation of Peroxide Ions on La 2 O 3 and Nd 2 O 3 under O 2 : Effects of Excitation Wavelength and Crystal Structure

Photoinduced formation of peroxide ions on La 2 O 3 and Nd 2 O 3 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 La 2 O 3 at 450 °C. By contrast, photoexcitation at 785 nm does not cause formation of O 2 2− up to 500 °C. Photoexcitation at 325 nm can induce O 2 2− formation on cubic Nd 2 O 3 at 25 °C, but cannot induce O 2 2− formation on hexagonal Nd 2 O 3 up to 200 °C. The significant difference in the behavior of O 2 2− formation over the Nd 2 O 3 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 Nd 2 O 3 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 Nd 2 O 3 is more favorable to the reaction of O 2 with O 2− to generate O 2 2− . The structural similarity between cubic Nd 2 O 3 and Nd 2 O 2 (O 2 ) may be another factor in favor of peroxide formation.