Broadband photoluminescence in a ceramic (Mg2SnO4–SnO2):Cr3+ system

This study reports the synthesis and photoluminescence spectroscopic studies of Cr3+-doped Mg2SnO4–SnO2 ceramics. The crystal structure was analyzed by X-ray powder diffraction, and photoluminescence was investigated at room temperature. The diffractogram confirmed the presence of Mg2SnO4 and SnO2 phases. Photoluminescence spectroscopy identified broad and intense emission bands assigned to the Cr3+ cation occupation in octahedral Mg2SnO4 sites and an orange band assigned to SnO2 emission. All spectra were analyzed and interpreted according to crystal field theory and Tanabe–Sugano theory for the d3 electronic configuration. The broad and intense emission band covering the visible/near-infrared region suggests that this system may be a promising material for use as an active medium in a broadband light source at room temperature.

Chemical disorder determines the deviation of the Slater-Pauling rule for Fe2MnSi-based Heusler alloys: evidences from neutron diffraction and density functional theory

Fe2MnSi fails to follow the Slater-Pauling rule. This phenomenon is thought to originate from either: (i) an antiferromagnetic arrangement of Mn ions at low temperature and/or (ii) chemical disorder. An important insight on this issue could be achieved by considering Fe2MnSi1-x Ga x compounds, thoroughly studied here by means of magnetization, neutron diffraction and density functional calculations (DFT). Our results indicate that chemical disorder (and not the antiferromagnetic arrangement) is responsible for the deviation of the Slater-Pauling rule on Fe2MnSi-based Heusler alloys. Furthermore, evidences suggest that Ga substitution into Si site favors the Fe/Mn disorder, further enhancing the observed deviation.

Fe3+ concentration dependence of photoacoustic absorption spectroscopy on ZnGa2O4 ceramic powders

In this paper we present the photoacoustic spectroscopy of ZnGa2O4 with 5 and 10% of Fe3+. The ZnGa2O4 is a normal spinel, with Zn2+ ions in tetrahedral sites and Ga3+ ions in octahedral sites. It is expected for these hosts that Fe3+ ions occupy Ga3+ sites. Therefore, the optical properties would be associated to an octahedral symmetry. The energy levels were identified and the crystal field and electronic interaction parameters calculated with Tanabe-Sugano matrices for d5 configuration. We have also studied the dependence of the photoacoustic signal amplitude on the excitation light modulation frequency. Our results indicate that thermal expansion is the predominant phenomenon for the photoacoustic signal generation.