Photoluminescence of lanthanide NASICONs: Na₅LnSi ₄O₁₂, Ln = Eu, Tb

Electrical materials incorporating lanthanide ions have great potential as electro-optical multifunctional systems. Polycrystalline NASICON (sodium silicon conductor) fast-ion conductors (Na₅LnSi₄O₁₂, Ln = Eu, Tb) have been prepared via solid-state synthesis. These materials have been characterized by photoluminescence spectroscopy, including steady-state emission and excitation spectra, and measurement of the lifetimes of the excited states. Two Eu³⁺ sites have been detected: (i) in regular framework positions, and (ii) replacing Na⁺ ions in the tunnels. Samples containing only Eu³⁺ or Tb³⁺ emit mainly from one transition, respectively, ⁵D₀ → ⁷F ₂ (610 nm, red) and ⁵D₄ → ⁷F₅ (550 nm, green). Mixed lanthanide samples, Na ₅Eu_0.75Tb_0.25Si₄O₁₂ and Na₅Eu_0.25Tb_0.75Si₄O₁₂, have also been prepared and efficient Tb → Eu energy transfer has been observed for the latter.