BiFeO 3 exhibits a complex phase-transition sequence under pressure associated with changes in octahedron tilts and displacements of Bi 3+ and Fe 3+ cations. Here, we investigate the local structure of Fe 3+ as a function of pressure through absorption crystal-field spectroscopy in the 0-18 GPa range. We focus on the influence of phase transitions on the Fe 3+ off-center displacement through the energy (E) and oscillator strength (f d−d ) of the 4 T 1 and 4 T 2 Fe 3+ (3d 5 ) bands observed below the band gap (E gap = 2.49 eV) at 1.39 and 1.92 eV, respectively, at ambient conditions. Pressure induces linear redshift of both 4 T 1 and 4 T 2 bands, consistent with the compression of the FeO 6 octahedron under pressure. On the other hand, the transition oscillator strength (f d−d = 3 × 10 −5 ), enabled by both the exchange mechanism and the off-center Fe 3+ distortion, slightly increases with pressure. The absence of notable anomalies in the variation of E(P ) and f d−d (P ) through the phase sequence from the ferroelectric rhombohedral R3c phase to the nonpolar orthorhombic Pnma phase suggests a persisting off-center position of the Fe 3+ . While this local polarity is correlated and expected in the ferroelectric R3c phase, its presence in the high-pressure nonpolar Pnma phase indicates the presence of local polar instabilities.

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This work investigates the energy transfer from Ce3+ to Mn2+ in high transmission glass (HTG) doped with CeO2 and MnO through time-resolved spectroscopy to transform the solar spectrum into a more efficient red-enhanced spectrum for traditional Si-based solar cells.

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