Synthesis, structure and VUV luminescent properties of rubidium rare-earth fluorides

RbF-LnF₃ (Ln=rare earth) systems were synthesized by hydrothermal technique. Under the hydrothermal condition, the light rare-earth elements form LnF₃ (Ln=La-Nd), while the heavy ones form RbLn₂F₇ (Ln=Y, Er, Yb and Lu) with the RbEr₂F₇ structure type. RbLn₃F₁₀ compounds were found for the in-between rare-earth cations (Ln=Eu-Tm and Y), which crystallize exclusively in the cubic γ-KYb₃F₁₀-type structure. The luminescent properties under vacuum ultraviolet light were studied for the Eu³⁺-doped RbLn₃F₁₀ (Ln=Y, Gd) and a high quantum efficiency of about 150% was observed for RbGd₃F₁₀:Eu³⁺.