University of Milano-Bicocca - UNIMIB DEPARTMENT OF MATERIALS SCIENCE The Department of Materials Science of the University of Milano-Bicocca has been founded in It includes a permanent staff of 44 researchers. Degree and Master courses in Materials Science Degree and Master courses in Chemistry Degree in Optical Technology European Ph.D. in Materials Science Ph.D. on Nanostructured Materials

RESEARCH GROUP: Inorganic Materials for Sensing and Photonics Main on-going investigation fields: 1.Defects in scintillators (tungstates, rare earth–doped perovskites, garnets, silicates, fluorides). 2. Micro-and nano-structured Hf-based luminescent materials. 3. Development of fiber sensors Some recent results: Anna Vedda, Norberto Chiodini, Mauro Fasoli, Irene Villa

Experimental facilities of the group: Synthesis laboratory Inorganic chemistry laboratory for sol-gel preparations. Film deposition by spin-coating. Furnaces for densification processes, instrumentation for optical finishing. Physical characterization laboratory optical absorption photo- thermo- and radio-luminescence spectroscopy ( K) micro-Raman scattering refractive index and film thickness thermostimulated currents ( K) complex impedance spectroscopy FTIR absorption ICP-Mass with laser ablation XRF Within collaborations XRD, SEM, TEM, AFM, DSC-TGA

Scintillation: Physical process High Energy photon absorption h h h h e e e e     Conduction Band Valence Band EgEg Luminescent Centre L exc L gnd Traps Photon ( VIS-UV ) CONVERSION TRANSPORT LUMINESCENCE

Compact Muon Solenoid detector in Large Hadron Collider in CERN, Geneva PbWO 4 -based calorimetric detector about 80,000 single crystal blocks of about 3x3x22 cm (12 m 3 ) Our previous investigations on scintillators

Material engineering: radiation resistance improvement in PbWO 4 Radiation induced absorption of PbWO 4 after gamma irradiation ( 60 Co) at RT Dose 500 Gy Thermoluminescence glow curves after X-ray irradiation at RT of PbWO 4 Radiation induced absorption is caused by the trapping of charge carriers by deep traps. Trapping can also be monitored by TSL measurements above RT, although the nature of defects causing optical absorption and TL peaks can be different. In the case of PbWO 4 deep traps are efficiently suppressed by trivalent ion doping (La, Y, Gd, Lu). S. Baccaro et al., Phys. Stat. Sol. 160, R5 (1997) M. Nikl et al., Appl. Phys. Lett. 71, 3755, (1997)

PWO:Pr and PWO:Mo for scintillation and Cerenkov DUAL READOUT

Optimization of both transparency and emission efficiency by tuning Mo concentration

Dosimetry of ionizing radiations by luminescence methods: application of scintillating glass optical fibers

Radio-luminescent RE-silica fiber-optics prepared by the sol-gel route. Sol-gel technique for fiber production Wet Gel Powder XGel Doped GLASS Powder Aging Rotating evaporator fast drying RTT 1600°C Sintering 1100°C Advantages: -High purity SiO 2 matrices -Doping (wide range of RE and concentrations) -Geometry: Bulk, thin films, powders RE-doped SiO 2 fiber-optics Powder in tube Inorganic polymerization of Si-alcoxide Sintering 1100°C Doped GLASS Rod Fiber drawing Rod (in tube) Slow drying at 40°C Sol Bulk XGel

Application in Medical Dosimetry Active portion Ce-doped SiO 2 Starlite s.r.l. PMT detection ELSE srl/Fraen srl Hard polymer clad multimode fiber Time RL Error < 1% below Cerenkov threshold High temporal resolution (luminescence decay time of Ce 3+ radiative transition: 50 ns)

RL response Vs dose rate - A. Vedda et al., Appl. Phys. Lett. 85, 6536 (2004). Some examples: Fiber response to 138 MeV proton irradiation I. Veronese et al., Rad. Meas. 45, 635 (2010). 60 Co gamma photons - E. Mones et al., Rad. Meas. 43, 888 (2008). Dose evaluation in CT Caretto et al., NIM A 612, 407 (2010)

Investigation on afterglow in CsI Co-doping with Bi induces a remarkable reduction of the afterglow signal, due to the presence of shallow traps in the crystal. The TSL signal is correspondingly reduced.

Preliminary data on CsI crystals Good reproducibility of the emission spectrum in two different samples Different light scattering properties

In summary: how can we investigate and control scintillator performance? Optical absorption (radiation damage) - OA Photoluminescence - PL/PLE Radioluminescence - RL Thermoluminescence (monitoring of defects) - TSL Time resolved luminescence Irradiation with x-rays