Luminescence and scintillation characteristics of four selected material systems, namely CsI:Tl(Na), CeF 3 , PbWO 4 and Ce-doped aluminium perovskites XAIO 3 :Ce (X=Y, Lu, Y-Lu) are reviewed. The progress in their physical understanding and related optimisation of their characteristics and technology are demonstrated. The important role of various defect states in the scintillator performance of these materials is stressed, which has led to the need for a deeper study of the processes of energy transfer and storage to achieve their intrinsic limits and full exploitation in scintillation detectors.

Wide Band Gap Scintillation Materials: Progress in the Technology and Material Understanding

Crystal Calorimetry in future high-energy physics experiments faces a new challenge to maintain its precision in a hostile radiation environment. This paper discusses the e⁄ects of radiation damage in scintillating crystals, and concludes that the predominant radiation damage e⁄ect in crystal scintillators is the radiation-induced absorption, or color center formation, not the loss of scintillation light yield. The importance of maintaining crystal’s light response uniformity and the feasibility to build a precision crystal calorimeter under radiation are elaborated. The mechanism of radiation damage in scintillating crystals is also discussed. While the damage in alkali halides is found to be caused by the oxygen/hydroxyl contamination, it is the structure defects, such as oxygen vacancies, cause damage in oxides. Material analysis methods used to reach these conclusions are presented in details. ( 1998 Published by Elsevier Science B.V. All rights reserved.

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Radiation damage in scintillating crystals

The changes in the absorption spectra induced by Co60 irradiation and high temperature annealing was studied for selected PbWO4 crystals. Based on radiation and annealings induced absorption spectra, four color centers are proposed, which could be responsible for shaping the absorption spectrum of PbWO4 crystals below 3.6 eV, namely Pb3+, O−, F, and F+ centers. Thermoluminescence (TSL) glow curves above room temperature were also studied on these samples to determine further the trap levels resulting from irradiation. Correlation between the results obtained by TSL and Co60 irradiation induced absorption changes is discussed.

Radiation induced formation of color centers in PbWO4 single crystals

The present work critically reviews the scientific and patent literature on low melting bismuth based oxide glass frits in materials for electronics, sensors and related applications such as sealing glasses, solar cells, architectural and automotive glass, the main motivation being to replace lead based materials by environmentally more benign ones. Due to similar glass forming properties of Bi and Pb, Bi based glasses are the closest ‘drop-in’ alternative for lead bearing formulations, and are therefore actually replacing them in many applications, helped also by previous experience with Bi containing materials in thick film technology and component metallisations. The outstanding issues are discussed, e.g. matching the lowest processing temperatures achieved by the classical lead based glasses without sacrificing durability and stability, as well as stability versus chemical reduction. Finally, consideration is also given to special ‘heavy’ glasses (often containing Bi and Pb together) that are ...

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Review of Bi2O3 based glasses for electronics and related applications

The optical transparency of PbWO 4 single crystals in the short wavelength region between 320 nm (cutoff) and 450 nm is significantly improved by doping with a small amount of La. This result indicates the possibility that the light yield detected by photomultipliers in actual detectors could be significantly increased for the fast blue emission which peaks around 420 nm. The improvement in transmittance was compared for different amounts of La doping. La-doping also shortens the decay time; the best fit of the decay spectrum is a sum of three exponentials for undoped PbWO 4 , while it is a sum of two exponentials for La-doped PbWO 4 with the absence of the next to the fastest component. GDMS analysis was carried out for the grown crystals to evaluate any other impurities.

Improvement in transmittance and decay time of pbwo4 scintillating crystals by la-doping

There are two types of crystals with respect to luminescence. In dc measurement, type A gives a primary emission at 410–430 nm (blue) with a second one at around 500 nm. Type B gives only dominant emission at 480–500 nm (green). This apparent difference can be interpreted as follows; the characteristic scintillation of PbWO4 is dominantly blue and subdominantly green. Intense phosphorescence with a decay constant of about 15 ms exists only in Type B at about 500 nm with one to two orders of magnitude larger intensity than scintillation, hiding the blue scintillation in its tail. The cause of the phosphorescence may be Mo.

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Scintillation and phosphorescence of PbWO4 crystals

Development of BSO (Bi4Si3O12) crystal for radiation detector

Single crystals of bismuth silicate were grown by the Bridgman method. The excitation and emission spectra are similar to BGO. The light output is 20% of BGO, giving FWHM energy resolution of 31% for 662 keV γ-rays ( 137 Cs). The decay constants are 2.4 ns (for 6% of intensity), 26 ns (12%) and 99 ns (82%). The radiation hardness against 60 Co γ-rays was about 10 5 –10 6 rad at the emission peak of 480 nm. Spontaneous recovery as well as optical annealing was also studied. BSO may be one the promising scintillators for high energy physics experiments.

Bismuth silicate Bi4Si3O12, a faster scintillator than bismuth germanate Bi4Ge3O12

Crystal growth of BSO (Bi4Si3O12) by vertical Bridgman method

We have achieved a considerable improvement in the growth of large Bi 4 Si 3 O 12 crystals, offering the possible application in γ-ray detectors at high energies. Clear blocks with transverse/longitudinal dimensions as large as 25 mm 200 mm were produced with good reproducibility. The pulse height uniformity along the longitudinal axis is within ±2%. The internal attenuation is less than 0.1%/cm at wavelengths above 400 nm. The radiation-induced optical absorption, which is about 2.5 m −1 at 10 4 rad (10 2 Gy) for the absorption coefficient at 480 nm, does not increase greatly even if the accumulated dose increases up to 10 8 rad. Spontaneous recovery continues for at least several tens of days, although the recovery is never complete. UV annealing occurs to some extent, in contrast to the case of BGO which darkens upon exposure to UV light. The scintillation characteristics are similar to those of small crystals reported previously. The light output is 25% of BGO and typical decay constants are 2.1 ns (for 6% of intensity), 40 ns (13%) and 112 ns (81%).

Kenji Harada

Papers

Scintillation and phosphorescence of PbWO4 crystals

Development of BSO (Bi4Si3O12) crystal for radiation detector

Bismuth silicate Bi4Si3O12, a faster scintillator than bismuth germanate Bi4Ge3O12

Crystal growth of BSO (Bi4Si3O12) by vertical Bridgman method

Large-size bismuth silicate (Bi4Si3O12) scintillating crystals of good quality