Structural and photoluminescence properties of doped and REE-endmember mixed-framework rare-earth sorosilicates

Photoluminescence (PL) properties of lanthanide-doped mixed-framework barium yttrium sorosilicates Ln:BaY₂(Si₃O₁₀) (Ln=Pr³⁺, Sm³⁺, or Er³⁺) and Ln:BaY₄(Si₂O₇)(Si₃O₁₀) (Ln=Pr³⁺, Sm³⁺, Er³⁺, or Ho³⁺), and selected REE-endmembers BaREE₂(Si₃O₁₀) (REE=Y, Dy) and BaREE₄(Si₂O₇)(Si₃O₁₀) (REE=Y, Er, Ho) are presented. These silicates were synthesized by a high-temperature, molybdate-based flux-growth method. Results from single-crystal structure refinements are given and briefly discussed in the spectroscopic context. Sm³⁺, present in both sorosilicate structure types, causes transitions in the visible yellow to orange spectral range at 600 and 570 nm, according to the ⁴G_5/2→⁶H_J transitions. Pr³⁺ is responsible for dominant PL bands around 500 nm due to the ³P₀→³H₄ transition, showing a blue-green emitting color. Er³⁺ exhibits green-yellow emission with strongest bands between 540 and 570 nm, which can be associated with the ⁴S_3/2→⁴I_15/2 transition. Ho³⁺ shows a dominant characteristic PL emission in the red spectral region, which is assigned to the ⁵F₅→⁵I₈ transition. The photoluminescence of emission of Dy³⁺ centers, with the main emission at 575 nm in the visible yellow region, is assigned to the ⁴F_9/2→⁶H_13/2 transition. Strong differences in the intensity of PL emissions of the REE-endmembers and Ln-doped silicates are caused by self-quenching effects due to high concentration of Ln³⁺ cations in the crystal structure. Unexpected PL emission spectra of the host sorosilicates BaY₂(Si₃O₁₀) and BaY₄(Si₂O₇)(Si₃O₁₀) are caused by trace impurity contents of other Ln³⁺ cations.