  We report the results of the investigation of the acoustic and optical
phonons in quasi-two-dimensional antiferromagnetic semiconductors of the
transition metal phosphorus trisulfide family with Mn, Fe, Co, Ni, and Cd as
metal atoms. The Brillouin-Mandelstam and Raman light scattering spectroscopies
were conducted at room temperature to measure the acoustic and optical phonon
frequencies close to the Brillouin zone center. The absorption and index of
refraction were measured in the visible and infrared ranges using the
reflectometry technique. We found an intriguing large variation, over ~28%, in
the acoustic phonon group velocities in this group of materials with similar
crystal structures. Our data indicate that the full-width-at-half-maximum of
the acoustic phonon peaks is strongly affected by the optical properties and
the electronic band gap. The acoustic phonon lifetime extracted for some of the
materials was correlated with their thermal properties. The obtained results
are important for understanding the layered van der Waals semiconductors and
for assessing their potential for optoelectronic and spintronic device
applications.
