Fe impurities inL-alanine: An EPR, luminescence, and Raman study

We present a study of low concentration Fe(III) doping in crystalline L-alanine by means of electron paramagnetic resonance, resonant Raman scattering, and photoluminescence. The magnetic resonance experiments show that Fe(III) occupies two inequivalent sites of rhombic symmetry in the L-alanine crystal. We obtain for the principal directions of the effective giromagnetic tensor the values gz=1.881(5), gy=4.641(8), and gₓ=7.238(5). In the optical experiments we find a selective resonant enhancement of some of the Raman active lattice vibrations comprising displacements of the hydrogen bonds between the carboxyl and ammonium groups of neighboring molecules. Based on these results we discuss the possible localization of the impurity in the crystal.