Theory of the broadening of vibrational spectra induced by lowered symmetry in yttria nanostructures

Abstract

We calculate the vibrational spectra for typical nanostructures including thin films, nanowires, and quantum dots of yttria, an important laser host material. Lattice dynamics calculations show that the vibrational spectra of nanocrystals are distinct from that of the bulk phase in the enhanced tails at low and high frequencies. Some of the low-frequency and high-frequency modes only involve surface atoms. Molecular-dynamics simulations are used to further decompose the contributions of surface and internal atoms, and the results confirm the evident broadening of the surface spectra. The broadening in vibrational spectra is attributed to the broadened atomic spring constants, further to the lowered symmetry of nanostructures.