Samarium-Doped Fluorochlorozirconate Glass-Ceramics as Red-Emitting X-Ray Phosphors

摘要

We have examined the photoluminescence (PL) and X-ray luminescence (XL) of fluorochlorozirconate (FCZ) glass-ceramics (FCZ-GC) doped with Sm~(3+) and Sm~(2+) ions. Sm-doped FCZ-GCs have been prepared by annealing a ZBLAN glass of nominal composition 53% ZrF_4, 20% NaF, 3% A1F_3, 3% LaF_3,1% SmF_3,1% BaF_2,19% BaCl_2 (mol%) above the glass transition of the host glass matrix. SmF_3 was added to the initial glass mix for trivalent samarium doping. Sm~(2+) doping was achieved by reducing Sm~(3+) to Sm~(2+) during the melting of the initial mix by the addition of NaBH_4. FCZ-GC contains BaCl_2 nanocrystals formed during the annealing with embedded Sm~(2+) ions, which dominate PL and XL. The PL of Sm~(2+) ions embedded in BaCl_2 nanocrystals strongly depends on their crystal structure (hexagonal or orthorhombic) and may be used to identify that structure. The correlation of the PL spectra with X-ray diffraction data is used to estimate the size of nanocrystals. The nanocrystals with average dimensions <～30 nm are mainly hexagonal while larger crystals are mostly orthorhombic. XL is more efficient in glass-ceramics containing relatively large BaCl_2 nanocrystals with hexagonal crystal structure.