The present work reports on the investigation of oxidation states, local symmetry, and optical properties of manganese and iron species in natural cordierite (Mg, Fe)2Al4Si5O18, by means of energy-dispersive X-ray fluorescence, electron paramagnetic resonance (EPR), photoluminescence (PL) and optical absorption techniques. In particular, specific EPR characteristics show the presence of distinct Mn2þ octahedral sites in the crystal lattice, and a small amount of Mn4þ ions in tetrahedral sites. The absence of EPR signal ascribable to Mn4þ in octahedral sites turns out to be consistent with the lack of narrow PL lines from d3 ions in octahedral crystal field (CF). Evidence of Mn3þ in octahedral sites is instead found in steady-state and time-resolved PL measurements. EPR spectra give further details on iron site occupancy, showing the occurrence of Fe3þ ions in octahedral sites. Characteristics ascribable to all the identified metal species have been found in the optical absorption spectrum or in the PL excitation spectrum, as arising from the expected CF transitions of Fe2þ, Fe3þ, Mn2þ, Mn3þ, and Mn4þ ions. Interestingly, the results show a polarization-dependent correlation between the manganese luminescence and the pleochroic absorption band at about 17,000 cm1. This result reveals a pleochroic contribution from the Mn3þ spin-allowed 5E!5T2 transition under the visible pleochroic band attributed to Fe2þ(oct)! Fe3þ(tet) transitions.
Mn sites in cordierite – electron paramagnetic resonance, luminescence, and optical absorption analysis
MOZZATI, MARIA CRISTINA;
2012-01-01
Abstract
The present work reports on the investigation of oxidation states, local symmetry, and optical properties of manganese and iron species in natural cordierite (Mg, Fe)2Al4Si5O18, by means of energy-dispersive X-ray fluorescence, electron paramagnetic resonance (EPR), photoluminescence (PL) and optical absorption techniques. In particular, specific EPR characteristics show the presence of distinct Mn2þ octahedral sites in the crystal lattice, and a small amount of Mn4þ ions in tetrahedral sites. The absence of EPR signal ascribable to Mn4þ in octahedral sites turns out to be consistent with the lack of narrow PL lines from d3 ions in octahedral crystal field (CF). Evidence of Mn3þ in octahedral sites is instead found in steady-state and time-resolved PL measurements. EPR spectra give further details on iron site occupancy, showing the occurrence of Fe3þ ions in octahedral sites. Characteristics ascribable to all the identified metal species have been found in the optical absorption spectrum or in the PL excitation spectrum, as arising from the expected CF transitions of Fe2þ, Fe3þ, Mn2þ, Mn3þ, and Mn4þ ions. Interestingly, the results show a polarization-dependent correlation between the manganese luminescence and the pleochroic absorption band at about 17,000 cm1. This result reveals a pleochroic contribution from the Mn3þ spin-allowed 5E!5T2 transition under the visible pleochroic band attributed to Fe2þ(oct)! Fe3þ(tet) transitions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
