Optical and EPR study of BaY2F8 single crystals doped with Yb

Optical and electron paramagnetic resonance study have been carried out on BaY2F8 single crystals doped with Yb ions at 0.5 and 10 mol%. The crystals have been obtained using the Czochralski method modified for fluoride crystal growth. Optical transmission measurements in the range of 190-3200 nm and photoluminescence measurements were carried out at room temperature. Absorption spectra of BaY2F8 single crystals doped with Yb due to the 2F7/2→2F5/2 transitions have been observed in the 930-980 nm range. To analyze the possible presence of Yb2+ ions in the investigated crystals, irradiation with γ-quanta with a dose of 105 Gy have been performed. The observed photoluminescence bands show usual emission in IR and other one in VIS, being an effect of cooperative emission of Yb3+ ions and energy up-conversion transitions of photons from IR to UV-vis(visible) due to hoping process between energy levels of paired Yb3+ and Er3+, where Er3+ ions are unintentional dopants. The EPR spectra of BaY2F8:Yb 10 mol% consist of many overlapping lines. They have been analyzed in terms of spin monomers, pairs, and clusters. The angular dependence of the resonance lines positions have been studied also to find the location of coupled ytterbium ions in the crystal structure.