Optimizing the performance of a glass-ceramic storage phosphor as an imaging plate for medical use

Europium-doped-fluorochlorozirconate glass ceramics, known as ZBLAN, were produced in a glove box which has a controlled environment of argon gas. For imaging applications BaCl₂ is used instead of BaF₂. Their properties after different thermal processing and different amounts of europium-doping were investigated. After annealing the ZBLAN glass, BaCl₂ nanoparticles are precipitated in the glass matrix. These glass ceramic storage phosphors are strong candidates for replacing traditional x-ray screen film system and commercial storage phosphors such as Agfa MD-30.

Differential scanning calorimetry (DSC) was used to determine the crystallization temperature of the hexagonal phase of BaCl₂, and orthorhombic BaCl₂ this in turn determines the subsequent annealing temperature. X-ray diffraction (XRD) and photoluminescence (PL) show that the hexagonal phase of BaCl₂ was formed upon annealing at temperatures between 250 °C and 280 °C for 5 minutes. The orthorhombic phase of BaCl₂, which has storage properties, was formed at higher annealing temperatures, at approximately 290 °C and above. Secondary ion mass spectroscopy (SIMS) was used to determine adsorbed/diffused oxygen content of the glass. The weight loss of fluorine and chlorine is 3-5 % and was determined using ion chromatography (IC). The concentration of other cations was determined using inductively coupled plasma spectroscopy (ICP). Transmission electron microscopy (TEM) was used to take high resolution pictures and verify the composition of BaCl₂ nanoparticles. The relative concentration of Eu²⁺ to Eu³⁺ of heated EuCl₃ and ZBLAN was studied using Mössbauer spectroscopy. The oxidation of Eu²⁺ to Eu³⁺ was also observed during the experiment. This study has reinforced the strong potential for application of glass-ceramic storage phosphors for medical imaging.