Local molecular structure and thermal expansion coefficient for octahedral Fe3+ center in AlF3:Fe3+system

A theoretical method for studying the inter-relation between electronic and molecular structure has been proposed by diagonalizing the complete energy matrices for d5 configuration ion in a trigonal ligand-field. Based on this method, the local lattice distortion of Fe3+ in AlF3:Fe3+ system (AlF3 is the component of fluoride glasses or is the single crystal) has been studied by considering the second-order and fourth-order EPR parameters D and (a − F), simultaneously. The results indicate that the local lattice structure around octahedral Fe3+ center has an expansion distortion whether AlF3:Fe3+ is the component of fluoride glasses or Fe3+ is doped in the AlF3 single crystal. The expansion distortion may be ascribed to the fact that the radius of Fe3+ ion is larger than that of Al3+ ion, and the Fe3+ ion will push the fluoride ligand outwards, respectively. Furthermore, the thermal expansion coefficient of Fe3+ in the single crystal AlF3:Fe3+ depending on the temperature are reported and some characteristics of it are also analyzed.