Vacuum ultraviolet spectroscopy ofCe3+-dopedSrMgF4 with superlattice structure

Abstract

X-ray diffraction of Ce3+-doped SrMgF4 (SMF:Ce) crystals shows a superlattice structure, reflecting the distribution ofCe3+ polyhedra centres observed in optical experiments. Optical absorption bands and fluorescence bands fromthe Ce3+ polyhedra centres overlap in the vacuum ultraviolet (VUV) and ultraviolet(UV) regions, respectively, so that wide pumping and tuning ranges areexpected for laser operation. The SMF:Ce crystals, as well as the isomorphousBaMgF4, are candidates for a tunable laser gain material with nonlinear properties.The optical absorption, excitation, and fluorescence bands observed in the SMF:Ce crystals atlow temperatures are ascribed to five distinct fluorescent centres. Three centres have well-knownCe3+ optical characters, for example, fluorescence with double peaks separated by2000 cm−1 and five resolved absorption/excitation bands. These centres are assigned toCe3+-polyhedra classified by weak and strong crystal fields as a consequence of thesuperlattice structure. The other two fluorescence bands observed in the visibleregion have 1.5–2 times larger linewidths than those of the former three bands.These bands are interpreted as optical transitions from complexes consisting ofCe3+ and one or two electrons trapped at a vacancy of the nearest neighbourF− ligand ions.