Temperature-Dependent Phonon Behavior in Nanocrystalline Tm2O3: Fano Interference and Phonon Anharmonicity

The temperature-dependent evolution of the vibrational properties of nanocrystalline cubic-phase thulium sesquioxide (Tm2O3) using Raman scattering is investigated in the 80–440 K temperature range. The phonon modes in the Raman spectra of the sample were found to exhibit a red shift with increase in the sample temperature. The most prominent Fg + Ag mode was observed at 383 cm–1; however, its line shape was found to be asymmetric in nature. Briet–Wigner–Fano (BWF) line shape was used to derive the vibrational characteristics of this mode. Further, the coupling coefficient, i.e., 1/q, was estimated, and the anharmonic parameters for the sample were also calculated in the given temperature range up to 440 K. The temperature dependency of the phonon frequency revealed three to six times greater magnitude of explicit anharmonicity as compared to that of implicit anharmonicity, with the dominance of the three-phonon process as determined by the line width of the peak with varying temperature.