Yb-doped double tungstates for down-conversion applications

The paper discusses the potential of several Yb-doped scheelite-like double tungstate crystals for sunlight down-conversion. Four hosts NaY(WO4)2, NaY1/2Gd1/2(WO4)2, NaY2/3Gd1/3(WO4)2, and NaY(Mo1/2W1/2O4)2 with the same 10% at. Yb doping level were comparatively investigated. Besides that, the effect of increase the Yb concentration from 10 at.% to 15 at.% was checked in case of NaY(WO4)2 crystal host. The efficient ytterbium 900-nm broadband emission was obtained under ultraviolet excitation, despite the absence of Yb absorption lines in this range. This happens due to non-radiative energy transfer from donor centers of the hosts to Yb active ions. This absorption wavelengths range of the host can be tuned by changing the crystal chemical composition. The obtained results indicate that the family of Yb-doped scheelite-like double tungstates is a suitable candidate for developing down-converter materials for solar energy applications.