Luminescence and X-ray phosphor properties of samarium and lanthanum-doped cubic barium chloride

Lanthanum and samarium-doped barium chloride samples with composition of the form Ba1-x-yLaxSmyCl2+x+y with x = 0.125 and 0 < y < 0.01 have been prepared in transparent ceramic form. X-ray diffraction confirms that the material adopts the high temperature cubic (fluorite) phase of barium chloride. The photoluminescence spectrum shows a combination of broad band 5d and narrow 4f transitions. The broad band can be decomposed into strong and weak components which we attribute to Sm2+ ions with and without an adjacent interstitial Cl- ion respectively. The temperature dependence of the strongest broad band indicates that the lowest 5d level is 800 cm-1 above the 5D0 level. The X-ray induced fluorescence spectrum shows an additional blue emission band for Sm concentrations y < 0.01 centred at around 420 nm which is ascribed to excitonic processes involving H centres. This emission band coincides with a photoluminescence excitation band for Sm2+ in this material, and so it is likely that the X-ray induced luminescence from Sm2+ arises via an energy transfer process. Scintillation arising from the blue band can be observed, but is characterised by a long tail extending over hundreds of microseconds. The relative efficiency of the material as an X-ray phosphor compared to commercial terbium-doped gadolinium oxysulphide is around 11%. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)