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guide the improvement. The complex spectroscopic analysis of the crystal after improvement is crystal properties. A model of the scintillation mechanism for PWO was developed and served to Further modifications of PWO technology were made to improve the uniformity of the ingot.phenomenon originates in the increase of point structure defects from top to bottom of the A different radiation hardness for top and bottom of the crystals was also observed. This radiating centres to the total luminescence band intensity. nm from top to bottom. This reflects the contribution variation of different kinds ofThe maximum of the scintillation luminescence band excited by Y-rays shifted from 490 to was decreasing from the top to the bottom of the ingot.samples cut from the bottom, indicating that the amount of effective scintillating centres yield from reference samples cut from the ingot top (seed side) was 50% higher than for A non-uniform light yield, from top to bottom of the crystal ingot was observed. The light features that suggest future technology improvements, involving the following characteristics: of 99.99% purity. These first crystals from a limited mass-production batch showed common crucibles in an atmosphere close to air in composition, using a mixture of W oxide and Pb oxide PWO crystals were grown by the Czochralski method in 100 mm diameter platinum resolution was GE/E = 3%/VE + 0.8%. hypothesis that (NbO3 + 1*+) centres replace (WO3 + F) centres without significantly acting on crystal, while no effect is seen on blue luminescence emission. This is in agreement with our A decrease of green luminescence intensity is noted with the increase of Nb content in the luminescence band with a maximum at 520 nm and an excitation of nearly 340 nm is observed.band described above as well as its excitation spectra have disappeared, while a new ions (PWO:Nb), the green luminescence intensity is slightly diminished, the red luminescence However, for doped crystal with a small amount (some 10*to 10of the mass) of Nb Luminescence and luminescence excitation spectra of doped by Nb and undoped samples 2.2 Doped and undoped crystal .· spectroscopic data (W O3 + F) centres they will decrease the amount of structure point defects with Pb3 produced by Nb5+ is shown in Pig. 2. Although (NbO3 + F+) centres will compete with significant change in structure point defect balance was found. A possible structure point defects optimal for this purpose. For PbWO4 crystals doped with Nb5+ in the w6* ion position, Pb3+ ions. This can be done by additional doping with ions of less valency -Nb5+ was found bottom of the crystal. A local compensation needs to be found to prevent the defects based on growth process, while the amount of defects connected with Pb3+ ions increases from top to bottom of the crystal ingot according to the abundance of W ions in the melt during the crystal centres at the top of the crystal. However, the amounts of these defects decrease from top to from a melt with some tungsten overabundance, in order to favor the do...

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