Optical properties of europium-activated hafnium fluoride-based glasses

We have studied the optical absorption, luminescence, and electron paramagnetic resonance of EuF₃- and EuF₂-activated fluorohafnate glasses. The glasses prepared with EuF₂ contain both di- and trivalent europium. The fraction of divalent europium clusters in the glass host decreases with decreasing EuF₂ concentration. Eu²⁺ luminescence in the fluorohafnate glasses is quenched, which is due the overlap of Eu²⁺ excited state levels with the conduction band of the glass, resulting in nonradiative relaxation through Hf³⁺ levels in the conduction band. The Eu³⁺ luminescence spectra contain lines corresponding to transitions from several levels of the ⁵D multiplet to levels of the ⁷F multiplet. The relationship between transitions from different ⁵D levels depends on europium concentration and temperature.