Radiation Measurements 38 (2004) 385–388 www.elsevier.com/locate/radmeas Radiation damage of doubly doped PbWO 4 :(Mo; A 3+ ) scintillator J. Pejchal a;b;∗ ,P.Bohacek b ,M.Nikl b ,V.Mucka a ,M.Pospisil a ,M.Kobayashi c ,Y.Usuki d a Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Brehova 7, 11519 Prague 1, Czech Republic b Institute of Physics AS CR ,Cukrovarnicka 10, Prague 16253, Czech Republic c KEK, High Energy Accelerator Research Organization, Tsukuba 305, Japan d Furukawa Co., Kamiyoshima, Yoshima, Iwaki 970-11, Japan Received 5 November 2003; received in revised form 5 January 2004; accepted 6 January 2004 Abstract Radiation-induced absorption spectra were measured to study the inuence of trivalent ion codoping (Y, La) on radiation hardness of PWO:Mo scintillators and to compare samples coming from two dierent laboratories. It follows from the experiments that trivalent ion codoping signicantly reduces the induced absorption coecient of PWO:Mo. At the same time, the shape of induced absorption spectra becomes more complicated and even bleaching of absorption after irradiation was observed in Y-codoped samples in the spectral region round 420 nm. When comparing Y and La-codoped samples, the positive eect of La is much less signicant than that of Y. Also, no absorption bleaching round 420 nm after irradiation was found in the latter case. c 2004 Elsevier Ltd. All rights reserved. Keywords: Radiation damage; Aliovalent ion doping; PWO; Colour centres 1. Introduction The PbWO4 (PWO) scintillator became the subject of in- terest because of its possible usage in radiation and particle detectors in high-energy physics accelerators, for example in large compact muon solenoid (CMS) detector in the large hadron collider (LHC) experiment in CERN. The main rea- sons consist in the fast response, low price, and relative ease of growth of large crystals using the Czochralski technique. The light yield is rather low (Nikl, 2000), but the possibil- ity to increase it at least by a factor of 2, while keeping its scintillation response reasonably fast, was reported recently (Nikl et al., 2000; Annenkov et al., 2000). During the scin- tillation process the transport of the thermalised charge car- riers is inuenced by their capture at various trapping states. ∗ Corresponding author. Department of Optical Crystals, Insti- tute of Physics ASCR, Cukrovarnicka 10, 16253 Prague, Czech Republic. Tel.: +420-2203-185-16; fax: +420-2333-431-84. E-mail address: pejchal@fzu.cz (J. Pejchal). This phenomenon may lead to a light yield decrease, slow- ing down of the scintillation decay kinetics, and material instability. The charge carriers trapped in deep traps form radiation-induced colour centres stable at room temperature as a result of the need for restoring a charge balance in the lattice. PWO is to be used in severe radiation environments in the mentioned applications, and therefore, stability of its scintillation characteristics is of crucial importance and study of radiation damage highly important. Reduction of concentration of traps and related defects (often cationic or anionic vacancies) can be achieved, for example, by aliovalent ion doping. The aliovalent ions introduce an unbalanced charge in the lattice and can therefore, sig- nicantly change the concentration of intrinsic point de- fects and consequently the concentration of colour centres (Nikl, 2000). The aim of this work was to study the inuence of triva- lent ion A 3+ (Y or La) codoping in PWO:Mo and to com- pare the samples coming from two dierent laboratories and eventually to investigate the possible inuence of Mo con- centration on the radiation hardness. 1350-4487/$-see front matter c 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2004.01.018