A. Edgar

Photostimulated luminescence in Eu-doped fluorochlorozirconate glass ceramics

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.

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

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 ...

Spatially resolved measurement of high doses in microbeam radiation therapy using samarium doped fluorophosphate glasses

The measurement of spatially resolved high doses in microbeam radiation therapy has always been a challenging task, where a combination of high dose response and high spatial resolution (microns) is required for synchrotron radiation peaked around 50 keV. The x-ray induced Sm3+ → Sm2+ valence conversion in Sm3+ doped fluorophosphates glasses has been tested for use in x-ray dosimetry for microbeam radiation therapy. The conversion efficiency depends almost linearly on the dose of irradiation up to ∼5 Gy and saturates at doses exceeding ∼80 Gy. The conversion shows strong correlation with x-ray induced absorbance of the glass which is related to the formation of phosphorus-oxygen hole centers. When irradiated through a microslit collimator, a good spatial resolution and high “peak-to-valley” contrast have been observed by means of confocal photoluminescence microscopy.

PHOTOSTIMULATED LUMINESCENCE IN A RARE EARTH-DOPED FLUOROBROMOZIRCONATE GLASS CERAMIC

Photostimulated luminescence at room temperature was observed in a fluorozirconate glass which was doped with 1% Eu2+ or 1% Ce3+ and 5% Br− ions. Small crystals of BaBr2 (high-pressure phase) form in the glass on cooling. The Eu2+ and Ce3+ luminescence spectra comprised two emission lines each: for Eu2+ one line at 413 nm and a broader band centered at 485 nm, and for Ce3+ one line at 320 nm and a broader band at 425 nm. The luminescence is attributed to the 5d14fn−1→4fn emissions of the rare earth ions. In both cases only one of the emission bands showed photostimulated luminescence. The stimulation band for both rare earth ions was centered at 570 nm.

Optically stimulated luminescence in NaMgF3:Eu2+

Optically stimulated luminescence (OSL) and thermoluminescence (TL) measurements were performed on polycrystalline NaMgF3:Eu2+ as well as sintered and quenched NaMgF3:Eu2+ after exposure to ionizing radiation. The authors find a range of TL traps and the sintering and quenching process reduces the concentration of shallow traps. The resultant time integrated OSL intensity is linear from microgray dose levels to approximately 100Gy, and hence this material is suitable for a personal and environmental dosimetry, where low dose levels are encountered and high sensitivity is required.

Structural phase changes in barium bromide nano-crystals in a fluorobromozirconate glass-ceramic x-ray storage phosphor

The structural changes in a fluorobromozirconate glass ceramic containing a ratio of 5% bromine to fluorine ions, following thermal annealing in the range 240-300 °C, are reported. The changes were monitored through x-ray diffraction, and the photoluminescence (PL) and electron paramagnetic resonance of Eu2+ dopant ions. In the range of 240-275 °C, the barium and bromine ions in the glass precipitate to form the metastable hexagonal phase of barium bromide. The Eu2+ PL spectrum comprises a narrow band at 410 nm, and a weaker broad band centred at 485 nm. The 410 nm band is assigned to two unresolved 4f65d1→4f7 emissions from Eu2+ ions at the two Ba2+ sites in this phase, whilst the 485 nm band is assigned to an impurity associated site or cluster. On annealing at 290 °C, the hexagonal phase transforms to the stable orthorhombic phase, and the PL spectrum comprises a single narrow band centred at 404 nm, assigned to a 4f65d1→4f7 emission from Eu2+ ions at the single Ba2+ site in the orthorhombic phase.

X-ray induced Sm3+ to Sm2+ conversion in fluorophosphate and fluoroaluminate glasses for the monitoring of high-doses in microbeam radiation therapy

Fluorophosphate and fluoroaluminate glasses doped with trivalent samarium were evaluated as sensors of x-ray radiation for microbeam radiation therapy at the Canadian Light Source using the conversion of trivalent Sm3+ to the divalent form Sm2+. Both types of glasses show similar conversion rates and may be used as a linear sensor up to ∼150 Gy and as a nonlinear sensor up to ∼2400 Gy, where saturation is reached. Experiments with a multi-slit collimator show high spatial resolution of the conversion pattern; the pattern was acquired by a confocal fluorescence microscopy technique. The effects of previous x-ray exposure may be erased by annealing at temperatures exceeding the glass transition temperature Tg while annealing at TA < Tg enhances the Sm conversion. This enhancement is explained by a thermally stimulated relaxation of host glass ionic matrix surrounding x-ray induced Sm2+ ions. In addition, some of the Sm3+-doped glasses were codoped with Eu2+-ions but the results show that there is no marked ...

In situ generation of Eu2+ in glass-forming melts

Abstract We report on the efficacy of in situ reduction of Eu 3+ to Eu 2+ in a fluoride melt by a variety of chemical reductants and by bulk electrochemical reduction. The Eu 2+ content of the resultant glasses was determined by a combination of electron paramagnetic resonance and magnetic susceptibility measurements. Addition of LiH, or use of a hydrogen atmosphere, produced near-complete reduction, whilst the electrochemical technique produced approximately 30% conversion. None of the fluorozirconate glasses luminesced from Eu 2+ ions, although a fluoroaluminate glass made using the LiH reduction technique did luminesce.

Photoluminescence and crystallization in europium-doped fluorobromozirconate glass-ceramics

Abstract We have investigated barium bromide crystallization in glasses which have an overall composition of 53% ZrF 4 , 20% BaF 2 , 5% NaF, 15% NaBr, 1% LaF 3 , 3% AlF 3 , 2% YF 3 , and 1% EuF 2 . The glasses were prepared by melting at 850°C in an inert atmosphere and quenching into a brass mold. Subsequent thermal treatment of the glass yields a transparent or translucent fluorozirconate glass containing BaBr 2 crystals; this glass-ceramic material has potential applications as an X-ray storage phosphor. The glasses and glass-ceramics were investigated using photoluminescence, optical density, X-ray diffraction, and differential scanning calorimetry methods. Glasses which have been quenched to temperatures below 260°C are transparent and show no photoluminescence from the europium ions. When the glasses are subsequently heated above about 263°C, crystals of BaBr 2 in the hexagonal phase start to precipitate and photoluminescence from Eu 2+ ions is observed. It is possible to prepare the resulting glass-ceramic in transparent form by heating to temperatures just below the temperature of most rapid crystallization, T x =280 C. The photoluminescence is attributed to Eu 2+ ions replacing Ba 2+ ions in the BaBr 2 crystals.

A new fluorozirconate glass-ceramic X-ray storage phosphor

A new fluorozirconate glass-ceramic has been discovered that displays an X-ray storage phosphor effect with an efficiency of up to 8% of that observed in the established crystalline storage phosphor, BaFBr:Eu 2+ . The glass-ceramic is based on the well-known ZBLAN20 formulation, but the replacement of Na by Rb and Li, partial substitution of F by Br, as well as doping with Eu 2+ , results in the formation of RbBa 2 Br 5 :Eu 2+ microcrystallites. X-ray diffraction, photostimulated luminescence and EPR measurements on the as-made glass and the annealed glass-ceramic show that the X-ray storage phosphor effect arises from the RbBa 2 Br 5 :Eu 2+ microcrystallites.