Crystal structure, infrared luminescence and magnetic properties of Tm3+-doped and Tm3+-, Dy3+-codoped BaY2Ge3O10 germanates

The Ca(Ba)RE2Ge3O10 germanates are currently considered as a promising class of active optical media emitting in the visible and infrared spectral region. Herein, a new series of BaY2-x-yTmxDyyGe3O10 phosphors was synthesized using the solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy, diffuse reflectance and luminescence spectroscopy. All the studied compounds crystallize in the monoclinic system, space group P21/m, Z = 2. Under 808 nm excitation, BaY2-xTmxGe3O10 germanates demonstrate a broad emission in 1.3–2.2 µm range owing to a series of cascade 3H4 → 3F4 and 3F4 → 3H6 transitions in Tm3+ ions. The BaY2-xTmxGe3O10 phosphors exhibit a high thermal stability over a wide temperature range and belong to promising infrared luminescence materials. The intensity of these emission bands decreases with an increase in the dysprosium content in the BaY1.97-yTm0.03DyyGe3O10 germanates. The magnetic properties measurements have been also carried out since Dy3+ ions exhibit a large magnetic anisotropy and non-collinearity of the magnetization easy axes. The magnetization curve of Tm3+-doped BaY2Ge3O10 shows the effects of saturation typical of paramagnetics, while the magnetization of germanates doped with Dy3+ ions occurs with hysteresis which is observed for single-ion magnets.