Inorganic scintillators Trends and perspectives Paul Lecoq CERN, Geneva This work is performed in the frame of the ERC Advanced Grant Agreement N°338953–TICAL

25 years of SCINT community actions New crystals development PWO La halide family LSO, LYSO, LGSO, LuAP, LuYAP, LuAG, …. Main emphasis (application driven: HEP & MI) was on: Understanding the material High light yield Good energy resolution (non-uniformity) Short decay time (for high event rate) Good radiation hardness (defect studies, compensation doping) Developping/adapting production technologies Czokralsky and Bridgeman for reacing desired specifications Investigating new technologies (mPD, ceramics,thin films, nano…)

4D Time Imaging Calorimeter Why fast timing in HEP? Search for rare events implies High luminosity accelerators Rate problems Pile-up Time of Flight techniques can alleviate the pile-up problem and help improving energy resolution, but: Current state of the art for Alice expt: 75ps Current state of the art for PET demonstrators: 140ps Need for a finely segmented calorimeter with 10ps time resolution 4D Time Imaging Calorimeter TICAL

How to extract the best time estimator from the signal? Crystal SiPM electronics q2 g Dt How to extract the best time estimator from the signal? Random deletion 2 SiPM PDE Random deletion 1 Absorption Self-absorption Unwanted pulses 2 DCR Unwanted pulses 1 DCR, cross talk Afterpulses tkth pe = Dt Conversion depth + tk’ ph Scintillation process + ttransit Transit time jitter + tSPTR Single photon time spread + tTDC TDC conversion time

New research directions P. Lecoq et al, IEEE Trans. Nucl. Sci. 57 (2010) 2411-2416 Besides all factors related to photodetection and readout electronics the scintillator contributes to the time and energy resolution through: The scintillation mechanism Light yield, Rise time, Decay time The light transport in the crystal Time spread related to different light propagation modes The light extraction efficiency (LYLO) Impact on photostatistics Weights the distribution of light propagation modes

Ways to a faster rise time? Rise time is to a large extent related to the multiple scattering and thermalization of hot primary e-h pairs More studies needed for self activated scintillators Probability for low energy transfer from ionizing radiation Direct excitation of the luminescent center It would be interesting to measure the rise time of PWO, BGO, CeF3 Cross luminescence: Core-Valence luminescence Sub ns rise time and decay time But UV-VUV emission (not maching SiPM QE) High donor band: ZnO, CuI, PbI2… Derenzo, NIMA 486 (2002) 214-219 Cerenkov Quantum dots????? What about Prompt photons? Intérêt CeF3: one atom/unit cell: no optical phonon, only acoustic phonons. Also gap in the conduction band (d sates og Ce3+

Light generation in a scintillator Rare Earth 4f 5d But this is based on a very simplified view of he pulse shpe, which consists of considering only the last part of a very complex energy conversion process in the scintillator Retour sur ce qui prend du temps pour amener l’excitation directe du Ce3+, ou les high donor band, etc…

Hot intraband luminescence Wide emission spectrum from UV to IR Ultrafast emission in the ps range Independant of temperature Independant of defects Absolute Quantum Yield Whn/Wphonon = 10-8/(10-11-10-12) ≈ 10-3 to 10-4 ph/eh pair Higher yield if structures or dips in CB? Interesting to look at CeF3 Vaisburd,.Evdokimov, phys.stat.sol.(c)2(205)216-222 M. Korzhik, P. Lecoq, A. Vasil’ev, SCINT2013 paper TNS-00194-2013

CeF3 hot intraband luminescence Fast 5ns CeF3 luminescence Tartu electron gun, 200keV, 200ps Regular 20ns CeF3 luminescence Fast interband hole luminescence < 200ps Fast interband e- luminescence < 200ps 200ps electron gun excittion 100to 200KeV V. Nagirnyi, S. Omelkov, Tartu, Estonia

Transient absorption M-Korzhik

Transient absorption Experimental bench to prove the concept Two photons(2,97+3.16eV) absorption in 1 cm thick PWO R&D to combine ionization and transient absorption is planned within AIDA-II and TICAL: 4D Time Imaging Calorimeter ERC project M-Korzhik

Transient absorption M-Korzhik

P. Lecoq, J.Grim, I.Moreels, SCINT conference CdSe Nanosheets Stimulated photoluminescence due to exciton quantum confimenet in CdSe nanoplatelets 100mm layer of CdSe nanoplatelets deposited on 1mm thick LSO crystal by J. Grim, IIT, Genova R. Turtos Matinez, CERN 525nm Exciton/biexciton emission obtained in the lab using LSO + CdSe nano deposition excited with blue laser. Electron pulse excitation experiments to come. P. Lecoq, J.Grim, I.Moreels, SCINT conference Berkeley, June 2015

Light Transport -49° < θ < 49° Fast forward detection 17.2% 131° < θ < 229° Delayed back detection 17.2% 57° < θ < 123° Fast escape on the sides 54.5% 49° < θ < 57° and 123° < θ < 131° infinite bouncing 11.1% To further improve we have to work on the light transport, and in particulr try to increase the number of direct photons transferred to the potodetector Improving light extraction efficiency at first hit on coupling face to photodetector is the key

Photonic crystals Nanostructured interface allowing to couple light propagation modes inside and outside the crystal Crystal- air interface with PhC grating: Crystal air θ>θc θ>θc Total Reflection at the interface θ>θc Extracted Mode

Photonic crystals 0° 45° Use large LYSO crystal: 10x10mm2 to avoid edge effects 6 different patches (2.6mm x 1.2mm) and 1 (1.2mm x 0.3mm) of different PhC patterns Review on photonic crystal coatings for scintillators International Journal of Modern Physics A A. Knapitsch, P. Lecoq Vol. 29 (2014) 1430070 (31 pages) A. Knapitsch et al, “Photonic crystals: A novel approach to enhance the light output of scintillation based detectors, NIM A268, pp.385-388, 2011

Chiral nanophotonic waveguide Controlling the flow of light with nanophotonic waveguides Transverse quantum confinement of guided photons  strong spin – orbit coupling Allows scattering of light by a nonoparticle at the surface of the nanofiber to be redirected in the direction of the fiber -49° < θ < 49° Fast forward detection 17.2% 131° < θ < 229° Delayed back detection 17.2% 57° < θ < 123° Fast escape on the sides 54.5% 49° < θ < 57° and 123° < θ < 131° infinite bouncing 11.1% Can be used to redirect in the direction of the photodetector >50% of the light emitted at large angle

New production technologies Micro-Pulling-Down: Marie Curie Rise-INTELUM project recently approuved – CERN coordinator Ce doped LuAG Sintillator undoped LuAG Cerenkov 30cm Ø 2mm

New production technologies Transparent Ceramics Reduced production cost Increased activator concentration Increased uniformity of doping Improved mechanical properties Production of large transparent samples of various shapes Potential to fabricate phases that can not be grown from melt Courtesy N. Cherepy, S. Payne, LLNL

New production technologies Thin films ZnO:Ga thin films on Si(100) are deposited by reactive DC magnetron sputtering of zinc in oxygen/argon mix, followed by vacuum annealing 60 ps ZnO:Ga powder Courtesy R. Williams, Wake Forest University

Conclusions R&D in inorganic scintillators is moving fast Timing performance is becoming a key R&D focus for many applications (HEP, MI, Homeland security, …) Enabling technologies are being developped Crystal production Nanophotonics for the management of optical photons A rapidly moving field with an enormous industrial potential and demand 3D ranging Photo-electronic chips Quantum entanglement and quantum computing Etc….