The Scintillation Mechanism in PbWO 4 Crystals
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M.V. KORZHIK*, V.B. PAVLENKO*, V.A. KATCHANOV**, JEAN-PIERRE PEIGNEUX*** AND MAURICE POULET*** *Institute of Nuclear Problems, 11 Bobruiskaya, Minsk 220050, Belarus "**Institute for High Energy Physics, Protvino, Russia ***LAPP-IN2P3, Annecy, France
ABSTRACT A mechanism of scintillations based on sensitisation of radiating centres luminescence by Pb2 + ions is proposed for PbWO 4 crystals.
INTRODUCTION It has been shown recently [1-3] that scintillators based on PbWO4 (PWO) single crystals are promising candidate for electromagnetic calorimetry in LHC. The luminescence properties of PbWO4 crystals are under investigation since the 40th. Nevertheless until now no general agreement in the luminescence centres origin. Kr~ger [4] by measuring of various tungsten compounds had found blue and green luminescence for PWO and attributed them to tungsten groups, surrounded by Pb2 + ions. Blasse and Bril [5] proposed that blue luminescence is caused by 6p 6s -- 6s2 transitions of Pb 2 + ions or due to a charge transfer transitions within the tungsten group and that green-yellow emission connected with a charge transfer within tungsten group and Pb2 + ion. Van Loo [6, 7] leads to the conclusion that the blue luminescence is caused by transitions in isolated WO- groups and green luminescence which is superposition of two bands, is caused by the transfer of an electron occupying an orbital with mainly lead character to an empty orbital of an adjacent group with a predominantly d character. Blasse and Groenink [8] had found polarisation of the green luminescence which they had interpreted as luminescence of isolated W0 3 groups. They had correlated the blue luminescence with regular WO-groups linked to a lead ions. Green luminescence in PWO had been also explained by Reyt [9] as self trapped excitons radiation. Finally Grasser [10] had found a several luminescence bands, a blue one, two green, one yellow and two red ones. He explained green bands as intrinsic luminescence of relaxed exitons of (Pb-W04) type, yellow as W0 3 luminescence and red bands as F-centres luminescence. The absence of unique interpretation of the obtained data is mainly the reflection of the fact that luminescence characteristics of PWO crystals are very sensitive to the specific conditions of their synthesis. Even small changes of these conditions induce considerable variations of emission and absorption spectra. The luminescence band excited by y-rays had shown maxima varying between 460 and 520 nm according to crystal growth conditions. It indicates that observed emission is at least a superposition of some luminescence bands. The contribution of these luminescence bands radiating centres in total spectrum was found and energy transfer processes between them are forming the scintillation properties of PbWO 4 crystals. 285 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society
Scintillation mechanism investigation The investigated undoped and doped crystals were grown by Czochralski method in platinum crucibles in the atmosphere close t
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