NIR-VIS reflectivity spectra of some transition metal thiophosphates

Room temperature optical-reflectivity measurements on some transition metal thiophosphates were carried out in the near infrared and visible regions. The resulting spectra, interpreted on the basis of the <<transition metal weakly interacting>> model, agree well with earlier optical transmission measurements. Below the fundamental absorption edge, the observed features have been assigned to 3d-3d transitions occurring on the transition metal ion, while those observed at photon energies greater than the absorption threshold have been attributed to transitions from the valence bands to discrete 3d orbital levels or to the conduction bands. A more detailed information on the metal ion 3d levels energy distribution with respect to the valence band states belonging to the (P2S6)4- cluster and a more precise determination of the MPS3 absorption edge energy position have been obtained.