1,720,990 research outputs found
Optical-absorption spectra of crystal-field transitions in MnPS3 at low temperatures
No full textThe manganese thiophosphate (MnPS3) optical-absorption spectrum has been investigated as a function of temperature from 300 down to 10 K in the visible region. With decreasing temperature, the fundamental absorption edge shifts towards higher energies without changing its shape and an additional subband-gap feature appears. This structure has been attributed to transitions between the Mn2+ third excited state and the ground state. All the subband-gap structures exhibit a small temperature shift, in good agreement both with the crystal-field theory and with the so-called transition-metal weakly interacting model. The temperature dependence of the crystal-field parameters Dq, B, and C has been determined from the transition energies. These results support the hypothesis that MnPS3 is to be considered an ioniclike compound, as already suggested in the literature
ELECTRONIC CONDUCTION IN THE LAYERED SEMICONDUCTOR MNPS3
No full textThermopower, conductivity and photoconductivity measurements as a function of temperature, from 130 to 320 degrees C, have been carried out on manganese thiophosphate, MnPS3. The transport mechanisms involved in distinct temperature ranges and under different illumination conditions have been identified. At 130 degrees C a dark conductivity value of 8.6*10 -13 Omega -1 cm-1 has been measured, while photoconductivity values ranged from 8.8*10-13 to 6.1*10-8 Omega -1 cm-1. In particular, the dark conductivity process has been attributed to holes in the phosphorus 3pz valence band. The results have been interpreted on the basis of a model, already used for NiPS3, that assumes a weak, ionic, interaction between the transition-metal and the sulphur atoms. A possible energy distribution of both valence and conduction bands, together with Mn 3d levels, is also provided
CONDUCTION PROCESSES IN THE LAYERED SEMICONDUCTOR COMPOUND FEPS3
No full textWe have measured, as a function of temperature, the thermopower, the dc conductivity, and photoconductivity of FePS3 single crystals. For temperatures below 430 K the thermopower shows an activated behavior, whereas at higher temperatures it is almost temperature independent. The dc dark conductivity and photoconductivity are thermally activated over the entire investigated temperature range. Moreover, ac-conductivity measurements have been carried out as a function of both temperature and frequency from 400 Hz to 100 kHz in the 340 "500-K temperature region. The transport mechanisms involved in different temperature ranges have been identified. The results have been interpreted on the basis of a simplified energy-band scheme. © 1990 The American Physical Society
NIR-VIS reflectivity spectra of some transition metal thiophosphates
No full textRoom 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 > 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
Fluorescence spectra of the layered semiconductor compound MnPS3
No full textFluorescence measurements on MnPS3 layered semiconductor crystals, in the visible region, below their fundamental absorption thresholds, were carried out at room temperature. The resulting emission spectra show four overlapping structures, which fall in the region of intraion transitions for the Mn2+ 3d5 configuration. The results, deduced from deconvolution of the bands, agree well with those obtained from optical-absorption measurements and furthermore confirm the Mn2+ 3d energy-level distribution derived from the transition-metal weakly interacting model. From the analysis of the excitation spectrum for the MnPS3 fluorescence band centered at 2.23 eV, additional information about the Mn2+ 3d excited-energy-state distribution and a verification of the validity of the above model are obtained
- …
