Photoinduced Formation of Peroxide Ions on La2O3 and Nd2O3 under O2: Effects of Excitation Wavelength and Crystal Structure.

Photoinduced formation of peroxide ions on La2O3 and Nd2O3 under O2 was studied by in-situ microprobe Raman spectroscopy with attention focused on the effect of excitation wavelength and crystal structure on the O2(2-) formation. It was found that photoexcitations at 633, 532, 514, and 325 nm can induce O2(2-) formation over La2O3 at 450 °C. By contrast, photoexcitation at 785 nm does not cause formation of O2(2-) up to 500 °C.

Mechanistic aspects of photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) under oxygen.

The photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) was studied by in situ microprobe Raman spectroscopy using a 325 nm laser as excitation source. It was found that the Raman bands of peroxide ions at 833-843 cm(-1) began to grow at the expense of the Ln(3+)-O(2-) bands at 333-359 cm(-1) when the Ln2O3 samples under O2 were continuously irradiated with a focused 325 nm laser beam at temperatures between 25-150 °C. The intensity of the peroxide Raman band was found to increase with increasing O2 partial pressure, whereas no peroxide band was detected on the Ln2O3 under N2 as well as on the samples first irradiated with laser under Ar or N2 followed by exposure to O2 in the dark.