Hydrothermal growth and properties of KGdF₄

The hydrothermal phase equilibria of the KF-GdF₃-H₂O system were studied at a temperature of 450°C and 10 kpsi. Crystals of K₂GdF₅, KGdF₄ and KGd₂F₇ were grown. The fluorides were found to be stable only with excess KF in solution. Research was subsequently focused on KGdF₄ synthesis, a potential material for 1.3 μm optical amplifiers when doped with Pr and Yb. Solubility and P-V-T measurements were used to determine conditions for the formation of KGdF₄ single crystals doped with either Pr or Pr + Yb. Absorbance and fluorescence of these crystals are reported and compared with those for heavy metal fluoride glasses. These dopants were chosen in order to produce luminescence at a wavelength of 1.3 μm, an important wavelength for optical amplifiers for optical fiber communication. Energy transfer from Yb to Pr was demonstrated and concentration quenching occurred only at ∼ 10X the concentration seen for rare earths in glass hosts. The results can be used as a guide for co-doping other fluorides and for growing larger crystals of KGdF₄.