Identification of trivalent rare earth impurities in YF 3, LuF 3 and LiYF 4 by electron paramagnetic resonance

Abstract

Yttrium fluoride (YF 3), lutetium fluoride (LuF 3) and lithium yttrium fluoride (LiYF 4) are considered as potential host materials for laser and scintillator ions. YF 3 and LuF 3 are orthorhombic with space group Pnma (D 16 2h), while LiYF 4 is tetragonal with space group I4 1/a (C 6 4h) all with four molecules per unit cell. In the first class the trivalent Y-site is 9-fold coordinated by F ions and in the second 8-fold. Using electron paramagnetic resonance (EPR) in doped and undoped crystals different rare earth impurities have been identified from their typical hyperfine interaction and their spin Hamiltonian parameters have been determined. We show that trivalent rare earth impurities like Nd 3+, Yb 3+, Er 3+ and Ce 3+ substitute for Y 3+ (Lu 3+) in YF 3 (LuF 3) preserving the monoclinic local C s site symmetry of Y (Lu) ion. The same holds for LiYF 4 where the rare earth impurities maintain the local S 4 symmetry. In the undoped crystals the rare earth impurities come from traces in the starting materials.