Optical absorption and reflectivity study of the layered MnPSe_3 seleniophosphate

Abstract

Room-temperature absorption and reflectivity spectra of MnPSe3 seleniophosphate crystals have been analyzed from 1.0 to 5.5 eV. A general consistency has been found between the two types of data. From the absorption data an optical energy gap of 2.27 eV was deduced for this compound, in agreement with the literature. A weak and broad absorption band below the fundamental absorption edge was also observed. The reflectivity spectrum exhibits five structures, of which two are located below the fundamental absorption threshold, whereas the others are positioned at higher energies. Spectra have been found to be similar to those reported for the corresponding MnPS3 thiophosphate, with all the structures beyond the absorption edge shifted toward lower energies. For photon energies greater than absorption edge the MnPSe3 reflectivity spectrum also shows a similarity to those obtained for the cadmium and mercury seleniophosphates. With this resemblance taken into account, the observed structures have been interpreted in terms of both the so-called transition-metal weakly interacting model and the weak-crystal-field theory. A simplified energy-band diagram, in which the electronic transitions that are responsible for the noted absorption and reflectivity features are clearly indicated, is drawn.