Photostimulated luminescence from fluorochlorozirconate glass ceramics and the effect of crystallite size

Abstract

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.

Eu oxidation state in fluorozirconate-based glass ceramics

“…5 The peak at 406 nm is attributed to the 5d-4f transition of Eu 2+ in hexagonal BaCl 2 ; the origin of the less intense but broader emission at 485 nm is unknown. A similar band near 485 nm was reported in fluorozirconate glass ceramics containing small hexagonal phase BaBr 2 crystallites.…”

“…DSC provides information on the onset of the BaCl 2 crystallization whereas PL infers the structure of the BaCl 2 nanocrystals. 5 The DSC data of Eu-doped FCZ glasses with and without 0.5 mol % InF 3 are shown in Fig. 5.…”

“…Note that Eu 2+ does not luminesce in the glass matrix but in the BaCl 2 nanocrystals. 5,6 For this reason, the crystalline structure of the barium chloride nanoparticles is critical to potential applications, as scintillators and storage phosphors require vastly different light collection methodologies, i.e., readout mechanisms.…”

Rare-Earth Doped Fluorochlorozirconate (Fcz) Glasses And Glass-Ceramics: Selected Thermal Properties And X-Ray Luminescence In Samarium Doped Fcz

“…R Cl = C Cl /(C Cl + C F ). Commercial grade high purity SmF 3 and EuF 2 were used as dopants. The amount of rare earth doping was in the range of 0.05-2 mol %.…”

“…As was shown in previous papers, the annealing of the glass encourages the formation of BaCl 2 nanocrystals in the glass matrix and the luminescence of Eu 2+ ions in BaCl 2 crystals is responsible for both, scintillation and storage phosphor properties. 3 It is therefore necessary to have a good knowledge of the critical temperatures, where phase transformations take place in this glass system, as a function of composition.…”