Natural optical activity of f-f transitions in ErAl3(BO3)4 single crystal

- Natural circular dichroism and absorption spectra of ErAl3(BO3)4 crystal.
- Natural optical activities of f-f transitions in ErAl3(BO3)4 crystal.
- Very large natural optical activity of a vibronic f-f transition.
- Theoretical explanation of features of f-f transitions optical activity.
- Two non equivalent positions of Er3+ ion in one of the excited states.

Absorption and natural circular dichroism (NCD) spectra of ErAl3(BO3)4 single crystal were measured at 90 K in the range of 10,000-28,200 cm−1. The spectra were decomposed on the Lorentz shape components and the natural optical activities (NOA) of f-f transitions between Stark components of the ground and excited multiplets were found. The NCD spectra permitted us to find out existence of two non equivalent positions of Er3+ ion in one of its excited states, which are due to the local decrease of the crystal symmetry in this state. Very large NOA of a vibronic line was revealed. This phenomenon was accounted for basing on the new quantum mechanical formula for the NOA of electron transitions. The principle difference of the NOA properties of electric dipole allowed and parity forbidden transitions is discussed.

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