BaFBr doped with Eu 2+ is the most successful X-ray storage phosphor used for digital radiography so far. The mechanisms of information storage and subsequent read-out are, however, not yet fully understood. The present understanding of the structures and reactions of the radiation-induced point defects involved in these processes are critically discussed. The shortcomings of X-ray storage phosphor screens based on BaFBr : Eu 2+ are the inferior spatial resolution compared to conventional X-ray films. Also reviewed are therefore alternative storage phosphors such as alkali halides doped with Eu 2+ , Ga + , In + , or Tl + or elpasolites doped with Ce 3+ or Eu 2+ which are also promising with high figures of merit and potentially higher spatial resolution. A completely new approach is the use of suitably doped glasses and glass ceramics. First results on fluorozirconate glass ceramics with good storage and read-out properties are reviewed.

We report the results from a study of europium-doped fluorochlorozirconate glasses that have been thermally processed to induce nucleation and crystallization of BaCl2 crystallites. The resulting glass ceramics show a photostimulated luminescence (PSL) effect with a conversion efficiency which is up to 80% of that found in the commercial crystalline x-ray storage phosphor material BaFBr:Eu2+. Thermal processing for 20 min in the range 240–260 °C produces small (∼6–11nm) hexagonal BaCl2 crystallites, while temperatures in the range 270–290 °C lead to the formation and growth of larger (∼15–100nm) orthorhombic BaCl2 crystallites, as well as additional unidentified phases. We observe only weak PSL from glass ceramics containing hexagonal BaCl2 (∼0.1% conversion efficiency compared to BaFBr:Eu2+ at room temperature), but orthorhombic phase crystallites give rise to a much larger relative efficiency that increases with particle size, and reaches ∼80% for 100 nm diameter particles. The PSL is attributed to the excitation of electrons trapped as F centers in the BaCl2 crystallites, while the dependence on crystallite size is consistent with a PSL-inert surface shell of thickness ∼7nm surrounding the BaCl2 crystallites.

We report the synthesis of Eu2+- and chlorine-doped fluorozirconate glass-ceramics that show an intense photostimulated luminescence (PSL) after x-ray irradiation at room temperature. The PSL efficiency is up to 80% of that found in the well-known crystalline x-ray storage phosphor BaFBr:Eu2+, and it is the largest thus far reported for a glass-ceramic. We attribute the PSL to crystallites of orthorhombic BaCl2 that are formed after annealing above the glass temperature. Hexagonal BaCl2 crystallites are also observed after short annealing times, but they do not provide a measurable PSL signal. The photoluminescence peak from glass-ceramics containing orthorhombic BaCl2 crystallites occurs at 402 nm, and the stimulation band is centered at about 560 nm.

Rare-earth-doped fluorochlorozirconate (FCZ) glass-ceramic materials have been developed as scintillators and their properties investigated as a function of dopant level. The paper presents the relative scintillation efficiency in comparison to single-crystal cadmium tungstate, the scintillation intensity as a function of x-ray intensity and x-ray energy, and the spatial resolution (modulation transfer function). Images obtained with the FCZ glass-ceramic scintillator and with cadmium tungstate are also presented. Comparison shows that the image quality obtained using the glass ceramic is close to that from cadmium tungstate. Therefore, the glass-ceramic scintillator could be used as an alternative material for image formation resulting from scintillation. Other inorganic scintillators such as single crystals or polycrystalline films have limitations in resolution or size, but the transparent glass-ceramic can be scaled to any shape or size with excellent resolution.