In the present work, we report on the preparation of silicate glass containing crystals by means of melting a mixture of YbPO₄ xenotime structured crystals and SiO₂ nanoparticles. This nanoparticle mixture is used for preparation of large volume core preforms for laser active optical fiber. Temperature dependent sintering and fiber drawing experiments at temperatures up to about 2000 °C were conducted in order to assess the integrity of the crystals in the preform and fiber, respectively. The survival of YbPO₄ crystalline particles in silica was investigated by X-ray diffraction (XRD), electron probe microanalysis (EPMA), Raman spectroscopy as well as static and time resolved fluorescence measurements. It was found that the particles withstand the high-temperature steps during the fiber fabrication process. XRD and spectroscopic measurements suggest that the Yb ions are located in a crystalline but also in an amorphous silica-dominated surrounding in the fiber, suggesting the partial decomposition of the crystals during the fiber fabrication.