Dynamics of the deep red Fe3+ photoluminescence emission in feldspar

We present here new characteristics of the Fe3+ emission in feldspar using a combination of site/energy-selective spectroscopy and time-resolved photoluminescence at cryogenic temperatures. Although the variation in the peak energy of Fe3+ emission has been known to vary across feldspar samples depending on the composition and structure, it has never shown before that this emission can vary dynamically even within a single sample. We show that a strong excitation-energy dependent emission (EDE) occurs in Fe3+ for non-resonant excitation at cryogenic temperatures; this characteristic can be exploited for site discrimination within a complex feldspar sample. The radiative relaxation in Fe3+ (4T1 (G)→ 6A1(S)) is shown to be a dynamic process depending on whether the ion is excited using resonant or non-resonant transition. We suggest that during resonant excitation, the excited state electron of Fe3+ possibly undergoes a slow spin-lattice relaxation, a process that leads to a non first order effect in the phosphoroscence decay.