Current status and future prospects of inorganic scintillator research

1. Current status and future prospects of inorganic scintillator research Pieter Dorenbos 42nd Workshop: Innovative Detectors for Supercolliders Erice (Trapani), Italy-28 Sept - 4 Oct 2003 Interfaculty Reactor Institute

2. Scintillators for low energy (<3 MeV) gamma detection Ce3+ activated scintillators intrinsic scintillators Scintillators for electromagnetic calorimeters (GeV-TeV) Requirements speed light output and energy resolution density Future prospects and directions of research Outline

3. Cs2LiYCl6:Ce 2003 LuI3:Ce 2003 K2LaI5:Ce 2002 LaBr3:Ce 2001 LaCl3:Ce 2000 Lu2Si2O7:Ce 2000 RbGd2Br7:Ce 1997 Fast UV response Invention of the photomultiplier tube History of scintillators M. J. Weber J. Lumin. 100 (2002) 35

4. allowed 5d4f emission • fast  = 15-60 ns • absence of slow 4f 4f emission • em depends on host • fluorides 300 nm • oxides 400 nm • sulfides 500 nm • dopant in high density La, Gd, and Lu-compounds

5. X-ray excited emission spectra of Ce3+, Pr3+, and Nd3+ • em depends on • lanthanide • host • 250 nm < Ce < 700 nm • 210 nm < Pr < 400 nm • Nd < 200 • slow 4f4f emission Pr and Nd

6. df emission in Ce, Pr, Nd

8. NaI:Tl R = 2.9 % LaBr3:Ce 61. 103 ph/MeV 18 ns 5.3 g/cm3 Scintillator performances Pulse-height spectra (662 keV gamma rays) R = 6.5 % 43. 103 ph/MeV 230 ns 3.7 g/cm3 Interfacultair Reactor Instituut

9. 60Co spectrum measured with prototype LaBr3:Ce scintillator

10. Speed of impurity activated scintillators

11. Radiative decay rate • dipole and spin allowed transitions • lanthanide 5d4f emission Ce3+, Pr3+, Nd3+, Eu2+ • s2-elements Tl+, Pb2+, Bi3+ (spin forbidden) • charge transfer luminescence • core valence luminescence • Yb2+ + hVB Yb3+

12. Limits to the decay time of impurity activated scintillators

13. Ce luminescence ~ 15-25 eV Core-Valence luminescence Core-valence Luminescence in Cs2LiYCl6:Ce3+ CB 5d 2F5/2 4f 2F7/2 VB 3p Cl Core 5p Cs Interfacultair Reactor Instituut

14. Properties of CVL materials • very fast decay 0.8-2 ns • poor light yield 700-2000 photons/MeV • CVL is only possible in K, Rb, and Cs halides, and BaF2 • it has never been observed in oxides • relatively low density

15. Efficiency of impurity activated scintillators

16. Intrinsic emission and slow transfer K2LaCl5:0.1%Ce K2LaBr5:0.7%Ce K2LaI5:0.7%Ce =24ns

17. LaCl3:Ce3+ emission and decay

18. LaI3 CB 5d 4f 0 (Q<<1) The LaX3:Ce series LaF3 CB LaCl3 5d LaBr3 CB 286 nm Number of thermalised electron-hole pairs  E / 2.5 Eg CB 5d 5d 4f 335 nm 356 nm 4f 4f Valence Band 2 (S<<1) 49 61 Light yield(103 ph/MeV) Interfacultair Reactor Instituut

19. LaBr3 Limits to the light output

20. Limits to the energy resolution Progress of past five years

21. Study of small band gap (3-4 eV) materials > 100.000 ph/MeV is feasible energy resolution below 2% @ 662 keV PD and APD readout of long wavelength Ce3+ emission present study LaI3:Ce3+ Eg  3.5 eV 450, 500 nm K2LaI5:Ce3+ Eg  4.5 eV 405, 445 nm LuI3:Ce3+ Eg  4.1 eV 475, 520 nm Future prospects impurity activated scintillators

22. Bunch spacing: b < 20 ns requirement: crystal length: > 25 cm creation time ionization track: i 1 ns light collection time: lc  3 ns ultimate response time: r 4 ns scintillation decay:  < 4 ns Scintillator requirements for the ELOISATRON calorimeter

23. Ce3+ is too slow Pr3+ and Nd3+ are faster, but in addition slow 4f4f emission. Emission at too high energy for read-out CVL is fast (ns) but limited to too low density (halide) materials Remaining option quenched luminescence ELOISATRON calorimeterspeed considerations

24. Internal luminescence quenching

25. X-ray excitation 406 nm laser excitation Eq=0.08 eV Eq=0.20 eV LaI3:Ce; quenching via the conduction band? T evolution Interfacultair Reactor Instituut

26. Quenching of PbWO4 emission

27. ELOISATRON calorimeterlight yield and resolution considerations • at TeV energies stochastic term and noise contribution vanish and last term remains • energy leakage • intercalibration errors • inhomogenities and radiation damage • temperature fluctuations Conclusion crystal quality is more important than light yield N.B. 1 photon/MeV106 photons/TeV light output can be traded off against faster decay

28. Requirement: optically transparent + high density transparency wide band gap inorganic compound absence of optically active electrons ions with closed shell configuration Density high atomic number of cations and/or anions small radius of cations and anions high ratio of cations to anions large packing fraction of the lattice ELOISATRON calorimeterdensity considerations

30. Density of binary compounds

31. Ionic radii of anions in inorganic compounds

32. High density of fluorides, oxides, and nitrides is related with small ionic radius Density LuF3<Lu2O3<LuN because of higher charge of anionlarger cation/anion ratio Nitride compounds is not a feasible option for calorimeter What compound can do the job? • Conclusion • The highest density compounds must be found amongst the oxides

33. Ionic radii of high atomic number cations

34. Density of ternary Lu-based compounds

35. Density of ternary Pb-based compounds

36. Ultimate density of 10 g/cm3 is feasible to obtain < 4ns, a quenched luminescence mechanism is needed impurity activation may introduce problems with transfer time concentration gradients inhomogeneity radiation hardness A quenched intrinsic luminescence mechanism is the best option Future prospects and directions for research

37. 3P11S0 emission in Pb2+ or Bi3+ Pb-compounds are more dense than Bi-compounds Pb-compounds with similar properties as PbWO4 but higher density should be searched for. Ce3+ emission in Pb-compounds has never been observed PbHfO3 has a density of 10.2 g/cm3 Future prospects and directions for research