Comparison of the phonons and electronic excitations of UO2 with different oxygen isotopes (16O, 18O), two purely electronic excitations at 4162 and 5778 cm−1 have been evidenced by their limited shift, when 16O is replaced by 18O. The bands observed at 570, 1144 and 2300 cm−1 in U16O2 shift to 545, 1091 and 2190 cm−1 for U18O2. The wavenumbers and the isotope shifts of these bands exhibit multiple relationships. It supports the assignments of the 1LO (~570 cm−1) and 2LO (~1144 cm−1) phonons for U16O2. Both bands exhibit marked decrease for increasing O/U ratio. The observed phenomenon is regarded as a good estimation of the stoichiometry of a uranium oxide. In addition, by analyzing the intensity ratios of the 2LO to 1LO phonons for various UO2 samples, the 2LO band is assigned to the Fröhlich interaction. Defect‐induced and/or deformation potential mechanisms play a dominant role for the 1LO band. Copyright © 2015 John Wiley & Sons, Ltd.

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High sensitivity and low spectral background of the Raman instruments are essential for the analysis of weak Raman-active samples. The design of the present portable fiber Raman probes leads to an interferential background that limits the application of the portable Raman technique in many situations. In this work, the spectral backgrounds of commercial probes with different optical configurations were analyzed, and the results indicated the backgrounds arose from the objective lenses and the dichroic filters. A universal solution was proposed, and a flat and clean background was achieved by utilizing the longpass optical configuration and an off-axis parabolic mirror. Combined with a high-throughput spectrometer with a research-grade CCD, this portable Raman equipment was successfully applied to identify the corrosion products on the surface of uranium (with extremely weak Raman signals). The developed portable Raman instrument with high sensitivity and low background is anticipated to be very useful for the on-site Raman detection of weak signals.