1. 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

2. 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…)

3. 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

4. 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

5. New research directions
P. Lecoq et al, IEEE Trans. Nucl. Sci. 57 (2010)
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

6. 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)
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+

7. 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…

8. 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/( )
≈ 10-3 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)
M. Korzhik, P. Lecoq, A. Vasil’ev, SCINT2013 paper
TNS

9. 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

10. Transient absorption
M-Korzhik

11. Transient absorption Experimental bench to prove the concept
Two photons(2, eV) 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

12. Transient absorption
M-Korzhik

13. 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

14. 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 %
49° < θ < 57° and 123° < θ < 131°
infinite bouncing %
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

15. 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

16. 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) (31 pages)
A. Knapitsch et al, “Photonic crystals: A novel approach to enhance the light output of scintillation based detectors, NIM A268, pp , 2011

17. 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 %
131° < θ < 229° Delayed back detection 17.2%
57° < θ < 123° Fast escape on the sides %
49° < θ < 57° and 123° < θ < 131°
infinite bouncing %
Can be used to redirect in the direction of the photodetector >50% of the light emitted at large angle

18. 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

19. 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

20. 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

21. 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….