Determination Of Charge-Compensated C-3 Upsilon (Ii) Centers For Er3+ Ions In Cdf2 And Caf2 Crystals

A unified theoretical method is established to determine the charge-compensated C-3v (II) centers of Er3+ ions in CdF2 and CaF2 crystals by simulating the electron paramagnetic resonance (EPR) parameters and Stark energy levels. The potential (Er3+-F--O-4(2-)) and (Er3+-F-7(-)-O2-) structures for the C-3v (II) centers of Er3+ ions in CdF2 and CaF2 crystals are checked by diagonalizing 364 x 364 complete energy matrices in the scheme of superposition model. Our studies indicate that the C-3v (II) centers of Er3+ ions in CdF2 and CaF2 may be ascribed to the local (Er3+-F--O-4(2-)) structure, where the upper ligand ion F- undergoes an off-center displacement by Delta Z approximate to 0.3 angstrom for CdF2 and Delta Z approximate to 0.29 angstrom for the CaF2 along the C-3 axis. Meanwhile, a local compressed distortion of the (ErFO4)(6-) cluster is expected to be Delta R approximate to 0.07 angstrom for CdF2:Er3+ and Delta R approximate to 0.079 angstrom for CaF2:Er3+. The considerable g-factor anisotropy for Er3+ ions in each of both crystals is explained reasonably by the obtained local parameters. Furthermore, our studies show that a stronger covalent effect exists in the C-3v (II) center for Er3+ in CaF2 or CaF2, which may be due to the stronger electrostatic interaction and closer distance between the central Er3+ ion and ligand O2- with the (Er3+-F--O-4(2-)) structure.