Encapsulating Luminescent Materials in Zeolites. III. Crystal Structure and Scintillation Properties of Cs,Na-LTA Treated with Zirconium Chloride Vapor

With the purpose of developing a new zeolite scintillator, fully dehydrated Cs,Na-A was exposed to ZrCl₄ (g, 3.7 × 10³ Pa) at 523 K. The crystal structures of Cs,Na-A and of the product, |Zr_0.14Cs_5.69Na_4.13Cl_0.85|[Si₁₂Al₁₂O₄₈]-LTA (Zr,Cs,Na,Cl-A), were determined by single-crystal crystallography using synchrotron X-radiation. The structure of Zr,Cs,Na,Cl-A was refined in the space group Pm3m (a = 12.230(1) Å) with all unique data to the final error index R₁ = 0.069 for the 639 reflections for which F_o > 4σ(F_o). Its composition was confirmed by scanning electron microscopy energy-dispersive X-ray analysis (SEM-EDX). Octahedral ZrCl₆^2- ions center 14% of the large cavities; each Cl^- ion bonds to an 8-ring Cs⁺ ion. These Cs⁺ ions bridge between ZrCl₆^2- ions to form a continuum with unit cell formula Cs₃ZrCl₆⁺ in the near-surface volume of the crystal. Other Cs⁺ ions lie opposite 6-rings in the sodalite and large cavities; Na⁺ ions occupy the remaining 6-rings. Upon X-irradiation, Zr,Cs,Na,Cl-A luminesces bright sky blue; the emission band is broad, ranging from 370 to 750 nm, peaking at 480 nm. The integrated intensity of the emission is ca. 16 times greater than that of anthracene, a well documented scintillator. This intense luminescence appears to result from charge transfer within the ZrCl₆^2- ions.