1. Structure, bonding, and spectroscopy of actinides in crystals A quantum chemical perspective Zoila Barandiarán Departamento de Química & Instituto Universitario de Ciencia de Materiales Nicolás Cabrera Universidad Autónoma de Madrid, Spain. http://www.uam.es/zoila.barandiaran

2. 2 Structure, bonding, and spectroscopy of actinides in crystals A quantum chemical perspective Structure, bonding, and spectroscopy of actinides in crystals A quantum chemical perspective Actinides spectroscopy quantum chemical perspective in crystals advanced nuclear energy systems challenge basic and applied research societal interest: controversial energy source; security & waste problems open shells: 5f, 6d, 7s extreme conditions (temperature, pressure) ions in crystals, solid fuel and fission products (UO 2, PuO 2 ) large manifolds of excited states: 5f N, 5f N-1 6d 1, and others spectroscopy: a basic tool expected/exotic electronic structures beyond the gs figerprints of local structure and bonding figerprints of local structure and bonding models of coordination chemistry models of coordination chemistry

3. 3 U 4+ in Cs 2 GeF 6 Actinide ions doped in solids – an example point defect: + local distortion + local distortion + new electronic states in the energy gap + new electronic states in the energy gap how many states ? how to calculate them ? how many states ? how to calculate them ? N electrons formally in 5f, 6d shells in a crystal field N electrons formally in 5f, 6d shells in a crystal field

4. 4 f and d electrons in an octahedral field Pa 4+ in Cs 2 ZrCl 6

5. 5 f and d electrons in an octahedral field U 4+ in Cs 2 ZrCl 6 Pa 4+ in Cs 2 ZrCl 6

6. 6 Structure, bonding, and spectroscopy of actinides in crystals A quantum chemical perspective Structure, bonding, and spectroscopy of actinides in crystals A quantum chemical perspective A quantum chemical model (for ground and excited states) Results an overview type of results type of results accuracies accuracies a show case Conclusions and what is next

7. 7 Defect cluster Embedding host Relativistic (spin-orbit) Relativistic (spin-orbit) Electron correlation Electron correlation Large f n and f n-1 d 1 manifolds Large f n and f n-1 d 1 manifolds f n, f n-1 d 1 embedding-AIMP relativistic core-AIMP (ECP) relativistic core-AIMP (ECP) wave-function based correlation methods wave-function based correlation methods (CASSCF + MS-CASPT2) (CASSCF + MS-CASPT2) A quantum chemical model for ground and excited states for ground and excited states

8. 8 Material Cs 2 GeF 6 with U 4+ impurities Ab Initio Model Potentials as Effective Core+Embedding Potentials Active (cluster valence) (UF 6 ) 2- 68 electrons (UF 6 ) 2- 68 electrons Inactive (environment) Cs 2 GeF 6 Cs 2 GeF 6 Non-parametric & produced directly from the frozen orbitalsNon-parametric & produced directly from the frozen orbitals Inactive-active explicit interactionsInactive-active explicit interactions –Coulomb, Exchange, Linear independence Inactive (core) U [Kr],4f U [Kr],4f F 1s F 1s

9. 9 Embedded Cluster Hamiltonian Relativistic Cowan-Griffin-Wood-Boring Hartree-Fock all-electron atomic calculations + Frozen core approximation Coulomb Exchange + scalar relativistic Linear independence + AIMP recipe for representation of operators long-range local local 

10. 10 Embedded Cluster Hamiltonian Relativistic Cowan-Griffin-Wood-Boring Hartree-Fock all-electron atomic calculations + Frozen core approximation Coulomb Exchange + scalar relativistic Linear independence + AIMP recipe for representation of operators short-range spectral representation 

11. 11 Embedded Cluster Hamiltonian Relativistic Cowan-Griffin-Wood-Boring Hartree-Fock all-electron atomic calculations + Frozen core approximation + AIMP recipe for representation of operators Coulomb Exchange + scalar relativistic Linear independence

12. 12 Embedded Cluster Hamiltonian Perfect crystal lattice Perfect crystal lattice loop over lattice ions until convergence perform a single embedded-ion calculation (SCF, CASSCF) produce its embedding-AIMP out of its orbitals update the lattice embedding potentials end loop Self-onsistent Embedded Ion calculations Self-Consistent Embedded Ion calculations

13. 13 Embedded Cluster Hamiltonian

14. 14 Spin-orbit coupling / electron correlation Spin-orbit splittings depend on: spin-orbit couplings spin-free spectrum which demand: small CI space P large CI space G Use G space for the spin-free spectrum Use P space for the spin-orbit couplings An aproximate decoupling of correlation and spin-orbit

15. 15 Spin-free state shifted Hamiltonian Use P space for the spin-orbit couplings small CI space P large CI space G Use G space for the spin-free spectrum

16. 16 Spin-free state shifted Hamiltonian Use P space for the spin-orbit couplings small CI space P large CI space G Use G space for the spin-free spectrum  

17. 17 Spin-free state shifted Hamiltonian Use P space for the spin-orbit couplings Use G space for the spin-free spectrum – Codes: MOLCAS COLUMBUS Björn O. Roos et al., Lund University Russ M. Pitzer et al., Ohio State University EPCISO Valérie Vallet et al., Université de Lille

18. 18 – Cluster: (AnL 6 ) q- Details of the calculations  Embedded-cluster (embedding AIMP for ionic solids)  spin-free: CASSCF/CASPT2  Effective core potential (Cowan-Griffin-Wood-Boring based AIMP)  spin-orbit: sfss-SOCI [MRCI(S)] – Embedding potentials: ~ 500 AIMPs + 3000 point charges at experimental sites at experimental sites so that E(R) is stable so that E(R) is stable

19. 19 Details of the calculations  Embedded-cluster (embedding AIMP for ionic solids)  spin-free: CASSCF/CASPT2  Effective core potential (Cowan-Griffin-Wood-Boring based AIMP)  spin-orbit: sfss-SOCI [MRCI(S)] – Core AIMPs: An: [Xe,4f] 5d,6s,6p, 5f,6d,7s Cl: [Ne] 3s,3p – Valence basis sets: An: (14s10p12d9f3g)/[6s4p5d4f1g] Cl: (7s7p1d)/[3s4p1d]

20. 20 Details of the calculations  Embedded-cluster (embedding AIMP for ionic solids)  spin-free: CASSCF/CASPT2  Effective core potential (Cowan-Griffin-Wood-Boring based AIMP)  spin-orbit: sfss-SOCI [MRCI(S)] – SA-CASSCF: [5f,6d,7s] N – MS-CASPT2: An: 5d 10 6s 2 6p 6 [5f,6d,7s] N + 6 x Cl: 3s 2 3p 6

21. 21 Details of the calculations  Embedded-cluster (embedding AIMP for ionic solids)  spin-free: CASSCF/CASPT2  Effective core potential (Cowan-Griffin-Wood-Boring based AIMP)  spin-orbit: sfss-SOCI [MRCI(S)] – spin-free-state-shifted Spin-Orbit CI: Wood-Boring spin-orbit operator scaled by 0.9 Basis of double-group adapted functions MRCI(S) CAS[5f,6d,7s] N

22. 22 Results: type of results Local structure (ground/excited states) bond lengths, vibrational frequencies

23. 23 Results: type of results Local structure (ground/excited states) bond lengths, vibrational frequencies Wave functions (and their analyses) bonding interactions bonding interactions

24. 24 Results: type of results Local structure (ground/excited states) bond lengths, vibrational frequencies Wave functions (and their analyses) bonding interactions bonding interactions Absorption/emission spectra transition energies, transition moments, emission lifetimes transition energies, transition moments, emission lifetimes

25. 25 Results: type of results Local structure (ground/excited states) bond lengths, vibrational frequencies Wave functions (and their analyses) bonding interactions bonding interactions Absorption/emission spectra transition energies, transition moments, emission lifetimes transition energies, transition moments, emission lifetimes Mechanisms of energy transfer upconversion/quantum cutting mechanisms upconversion/quantum cutting mechanisms Green-to-blue light upconversion in Cs 2 ZrCl 6 : U 4+ U 4+ impurities 5f 2 levels UO 2 2+ impurities 5f 1 6d 1 levels

26. 26 Results: type of results Local structure (ground/excited states) bond lengths, vibrational frequencies Wave functions (and their analyses) bonding interactions bonding interactions Absorption/emission spectra transition energies, transition moments, emission lifetimes transition energies, transition moments, emission lifetimes Mechanisms of energy transfer upconversion/quantum cutting mechanisms upconversion/quantum cutting mechanisms Pressure effects Cs 2 NaYCl 6 :Ce 3+ under pressure P=0 P=25 kbar f1f1 d(t 2g ) 1 d(e g ) 1

27. 27 Results: type of results Local structure (ground/excited states) bond lengths, vibrational frequencies Wave functions (and their analyses) bonding interactions bonding interactions Absorption/emission spectra transition energies, transition moments, emission lifetimes transition energies, transition moments, emission lifetimes Mechanisms of energy transfer upconversion/quantum cutting mechanisms upconversion/quantum cutting mechanisms Pressure effects

28. 28 Results: accuracies (validation + applications) CePrNdPmSmEuGdTbDyHoErTmYbLu ThPaUNpPuAmCmBkCfEsFmMdNoLr Cs 2 NaYCl 6 Cs 2 ZrCl 6 Cs 2 GeF 6 SrF 2 BaF 2 YAG (Y 3 Al 5 O 12 ) Bond distances presumably (no EXAFS available) 0.01Å Bond length changes very good (exceptions?) Cs 2 ZrCl 6 :Pa 4+ YAG:Ce 3+ Vibrational frequencies 5% Ce 3+,Pr 3+,Sm 2+,Pa 4+ Electronic transitions 10% Ce 3+,Pa 4+,U 3+,U 4+ Pressure induced shifts of electronic transitions semiquantitativeSm 2+ Intensidades relativas semiquantitative Ce 3+,U 3+,U 4+ CsCaBr 3

29. 29 U 4+ in fluorides U 4+ 5f 2, 5f 1 6d 1 manifolds ~90 excited states U 4+ 5f 2, 5f 1 6d 1 manifolds ~90 excited states fluorides large transparency window fluorides large transparency window ● UV solid state laser ● Phosphor based on quantum cutting or cascade luminescence Potentiality as Results: a show case Predicting the luminescence of a new material + experimental & theoretical study

30. 30 5f 2 levels UV solid state laser Strong, broad, fast 6d → 5f luminescence quantum cutting or cascade luminescence 5f 1 6d 1 levels 1S01S01S01S0 YLiF 4 :U 4+ YF 3 :U 4+ Weak, slow, two-step 5f → 5f luminescence

31. 31 UV solid state laser quantum cutting or cascade luminescence U 4+ in Cs 2 GeF 6 The electronic structure of the 5f 2 manifoldThe electronic structure of the 5f 2 manifold The 5f 1 6d 1 manifoldThe 5f 1 6d 1 manifold Promote the synthesis and experimental study Promote the synthesis and experimental study An unexpected 5f 1 7s 1 manifold: U-trapped excitons An unexpected 5f 1 7s 1 manifold: U-trapped excitons

32. 32 Cs 2 GeF 6 :U 4+, a potential quantum cutter or solid state laser ? 1S01S01S01S0 5f 2 levels

33. 33 5f 2 levels quantum cutting or cascade luminescence 5f 1 6d 1 levels 1S01S01S01S0 1S01S01S01S0 3P03P03P03P0 3H43H43H43H4 5f 2 levels Cs 2 GeF 2 :U 4+, a potential quantum cutter or solid state laser ?

34. 34 1S01S01S01S0 5f 1 6d 1 levels 5f 2 levels Cs 2 GeF 2 :U 4+, a potential quantum cutter or solid state laser ? 5f 2 levels UV solid state laser Strong, broad, fast 6d → 5f luminescence 5f 1 6d 1 levels 1S01S01S01S0

35. 35 Miroslaw Karbowiak, University of Wroklaw growth of Cs 2 GeF 6 :U 4+ single crystals growth of Cs 2 GeF 6 :U 4+ single crystals experimental absorption spectrum (7 K) experimental absorption spectrum (7 K) broad, intense bands 37000 – 45000cm -1 broad, intense bands 37000 – 45000cm -1 no appreciable fine vibronic structure no appreciable fine vibronic structure most prominent at 38000 cm -1 most prominent at 38000 cm -1 Absorption spectrum.

36. 36 Theoretical spectrum Theoretical spectrum 2500cm -1 too high (0.3 eV) (7 %) 2500cm -1 too high (0.3 eV) (7 %) Five 5f 1 6d 1 origins: 1A 1g → iT 1u ( i = 1,5) Five 5f 1 6d 1 origins: 1A 1g → iT 1u ( i = 1,5) Absorption spectrum.

37. 37 Absorption spectrum. Intensities: Intensities: + most prominent band 1A 1g → 1T 1u + relative intensities ok, - except for 1A 1g → 2T 1u - except for 1A 1g → 2T 1u 2500cm -1 too high (0.3 eV) (7 %) 2500cm -1 too high (0.3 eV) (7 %) Five 5f 1 6d 1 origins: 1A 1g → iT 1u ( i = 1,5) Five 5f 1 6d 1 origins: 1A 1g → iT 1u ( i = 1,5) Theoretical spectrum Theoretical spectrum

38. 38 Emission spectrum. 1T 1g 1T 2g 2T 1g, 2T 2g 3T 2g 5f 2 levels 5f 1 6d 1 levels 1E u

39. 39 Large Stokes shift: 6200 cm -1 Emission spectrum. 1T 1g 1T 2g 2T 1g, 2T 2g 3T 2g 1A 1g 1E u

40. 40 Spontaneous emission lifetime:  Emission spectrum. Experiments underway

41. 41 An unexpected 5f 1 7s 1 manifold: U-trapped exciton? 2.154, 2.174, 2.21 2.154, 2.174, 2.21 Å 2.09 U(IV) Bond length ~ U(V) cluster Bond length ~ U(V) cluster Very diffuse 7s orbital Very diffuse 7s orbital Energy sensitive to basis set delocalization Energy sensitive to basis set delocalization U - trapped exciton ?

42. 42 An unexpected 5f 1 7s 1 manifold: U-trapped exciton? Impurity-trapped exciton D. S. McClure, et al. Phys. Rev. B, 32, 8465 (1985) SrF 2 :Yb 2+ anomalous emission “The excited state... could be called an impurity-trapped exciton, since it consists of a bound electron-hole pair with the hole localized on the impurity and the electron on nearby lattice sites...” “The trapped exciton geometry is probably that expected for a trivalent impurity ion, Yb 3+...” Impurity-trapped exciton D. S. McClure, et al. Phys. Rev. B, 32, 8465 (1985) SrF 2 :Yb 2+ anomalous emission “The excited state... could be called an impurity-trapped exciton, since it consists of a bound electron-hole pair with the hole localized on the impurity and the electron on nearby lattice sites...” “The trapped exciton geometry is probably that expected for a trivalent impurity ion, Yb 3+...” Yb 2+ → Yb 3+ + 1e(Sr) very short bond length localised hole delocalised Yb 2+ → Yb 3+ + 1e(Sr) very short bond length localised hole delocalised

43. 43 7s MO [5f 1 7s 1 -2 3 A 2u (UF 6 Cs 8 ) 6+ ] 7s AO [5f 1 7s 1 - 3 F U 4+ ] Analysis of the wavefunctions

44. 44 Hole localized Hole localized in the U(5f) in the U(5f) ~ U(V) bond length ~ U(V) bond length Diffuse orbitals of Ln/An in solids can lead to Diffuse orbitals of Ln/An in solids can lead to impurity trapped excitons Microscopic description of an impurity trapped exciton Electronic density Electronic density in the frontier of in the frontier of the UF 6 unit the UF 6 unit

45. 45 Wavefunction based ab initio embedded cluster calculations on Ln q+ and An q+ impurities in ionic hosts –Reliable enough (complement experiments, predict) –Can be used to progress in the understanding of Advanced Nuclear Energy Systems Advanced Nuclear Energy Systems Conclusions What is next ? Nuclear fuel and nuclear wastes materials –UO 2 (experimental spectroscopy available), PuO 2 –diluted UO 2 /PuO 2 mixtures UO 2 :Pu 4+, PuO 2 :U 4+ Transuranium systems (the f 7 configuration) –Cm 3+ in Cs 2 NaYCl 6 (experimental spectroscopy available) –and Am 2+ and Bk 4+

46. 46 Acknowledgments Luis Seijo Luis Seijo Belén Ordejón Belén Ordejón Ana Muñoz José Luis Pascual José Luis Pascual me me José Gracia José Gracia Fernando Ruipérez Fernando Ruipérez on campus, UAM 2006 Goar Sánchez Noémi Barros in La Sierra, Madrid 2007 http://www.uam.es/quimica/aimp/

47. 47 Acknowledgments Miroslaw Karbowiak, Faculty of Chemistry, University of Wroclaw, Wroclaw, PolandMiroslaw Karbowiak, Faculty of Chemistry, University of Wroclaw, Wroclaw, Poland Norman Edelstein, Lawrence Berkeley National Laboratory, Berkeley, California, USANorman Edelstein, Lawrence Berkeley National Laboratory, Berkeley, California, USA Björn Roos, Rolandh Lindh, (MOLCAS) Lund University, Lund, SwedenBjörn Roos, Rolandh Lindh, (MOLCAS) Lund University, Lund, Sweden Russell Pitzer, (COLUMBUS) Ohio State University, Columbus, Ohio, USARussell Pitzer, (COLUMBUS) Ohio State University, Columbus, Ohio, USA Valérie Vallet, Jean-Pierre Flament (EPCISO) Université de Lille, Lille, FranceValérie Vallet, Jean-Pierre Flament (EPCISO) Université de Lille, Lille, France Spanish Ministry of Education and Science, DGI-BQU2002-01316,DGI-CTQ2005- 08550.Spanish Ministry of Education and Science, DGI-BQU2002-01316,DGI-CTQ2005- 08550.

48. 48 Structure, bonding, and spectroscopy of actinides in crystals. A quantum chemical perspective Universidad Autónoma de Madrid