Micro-crystallization and spectroscopic properties of Er, Yb:RAl-borates (R=Y, Gd) obtained in RAl<inf>3</inf>(BO<inf>3</inf>)<inf>4</inf>-K<inf>2</inf>Mo<inf>3</inf>O<inf>10</inf>-B<inf>2</inf>O<inf>3</inf>-R<inf>2</inf>O<inf>3</inf> and RAl<inf>3</inf>(BO<inf>3</inf>)<inf>4</inf>-B<inf>2</inf>O<inf>3</inf> s

© 2016 Elsevier B.V.The spontaneous YAl3(BO3)4 (YAB) and GdAl3(BO3)4 (GdAB) crystals (of nominal composition and co-doped with Er and Yb) up to 4-5mm in length were grown from high-temperature solutions using K2Mo3O10 based fluxes in the temperature range of 1120-900°C. Glass-ceramic composites based on the YAB and GdAB micro-crystals have been prepared by quenching YAB-B2O3 and GdAB-B2O3 melts and characterized by X-ray diffraction and spectroscopic methods. The vitrified melt was shown to contain micro- and nano-crystalline rare-earth borate phases. Their distribution over the composites has been investigated by electron microscopy and three-dimensional X-ray tomography. The absorption spectra of these materials co-doped with erbium and ytterbium as well as luminescence spectrum were demonstrated