Structure, bonding, and spectroscopy of actinides in crystals A quantum chemical perspective

Structure, bonding, and spectroscopyStructure, bonding, and spectroscopyof actinides in crystalsof actinides in crystals

A quantum chemical perspectiveA quantum chemical perspective

Zoila BarandiaránZoila Barandiarán

Departamento de Química &Departamento de Química &Instituto Universitario Instituto Universitario dede Ciencia de Materiales Nicolás Cabrera Ciencia de Materiales Nicolás Cabrera

Universidad Autónoma de Madrid, Spain.Universidad Autónoma de Madrid, Spain.

http://www.uam.es/zoila.barandiaran

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Structure, bonding, and spectroscopyStructure, bonding, and spectroscopy of actinides in of actinides in crystalscrystals

A quantum chemical perspectiveA quantum chemical perspectiveActinidesActinides

spectroscopyspectroscopy

quantum chemical perspectivequantum chemical perspective

in crystalsin crystals

advanced nuclear energy systemsadvanced nuclear energy systemschallenge challenge basicbasic and applied and applied researchresearchsocietal interest: societal interest: controversial energy source; security & waste controversial energy source; security & waste problemsproblems

open shells: 5f, 6d, 7sopen shells: 5f, 6d, 7s

extreme conditions (temperature, extreme conditions (temperature, pressurepressure))ions in crystals, solid fuel and fission products (UOions in crystals, solid fuel and fission products (UO22, PuO, PuO22))

large manifolds of excited states: 5flarge manifolds of excited states: 5fNN, 5f, 5fN-1 N-1 6d6d11, and others, and othersspectroscopy: a basic tool spectroscopy: a basic tool

expected/exotic electronic structures beyond the gsexpected/exotic electronic structures beyond the gs figerprints of local structure and bondingfigerprints of local structure and bonding models of coordination chemistrymodels of coordination chemistry

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UU4+4+ in Cs in Cs22GeGeFF66

Actinide ions doped in solids – an exampleActinide ions doped in solids – an examplepoint defect:point defect:

+ local distortion+ local distortion + new electronic states in the energy + new electronic states in the energy gapgap

how many states ? how to calculate them ?how many states ? how to calculate them ? N electrons formally in 5f, 6d shells in a crystal fieldN electrons formally in 5f, 6d shells in a crystal field

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f and d electrons in an octahedral fieldf and d electrons in an octahedral field

PaPa4+4+ in Cs in Cs22ZrClZrCl66

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f and d electrons in an octahedral fieldf and d electrons in an octahedral field

UU4+4+ in Cs in Cs22ZrClZrCl66PaPa4+4+ in Cs in Cs22ZrClZrCl66

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Structure, bonding, and spectroscopyStructure, bonding, and spectroscopy of actinides in of actinides in crystalscrystals

A quantum chemical perspectiveA quantum chemical perspective

A quantum chemical model A quantum chemical model (for ground and excited states)(for ground and excited states)

ResultsResultsan overviewan overview type of resultstype of results accuraciesaccuraciesa show casea show case

Conclusions and what is next Conclusions and what is next

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Defect clusterDefect cluster Embedding hostEmbedding host

• Relativistic (spin-orbit)Relativistic (spin-orbit)• Electron correlationElectron correlation• Large fLarge fnn and f and fn-1 n-1 dd1 1 manifoldsmanifolds

ffnn , f , fn-1n-1dd11embedding-AIMPembedding-AIMP

• relativistic core-AIMP relativistic core-AIMP (ECP)(ECP)• wave-function based correlation wave-function based correlation methodsmethods (CASSCF + MS-CASPT2)(CASSCF + MS-CASPT2)

A quantum chemical modelA quantum chemical model for ground and excited states for ground and excited states

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MaterialMaterialCsCs22GeFGeF6 6 withwith

UU4+4+ impurities impurities

Ab InitioAb Initio Model Potentials Model Potentials as as Effective Effective Core+EmbeddingCore+Embedding Potentials Potentials

ActiveActive (cluster valence) (cluster valence) (UF(UF66))2- 2- 68 electrons68 electrons

InactiveInactive (environment) (environment) CsCs22GeFGeF66

• Non-parametric & produced directly from the frozen orbitalsNon-parametric & produced directly from the frozen orbitals• Inactive-active explicit interactionsInactive-active explicit interactions

– Coulomb, Coulomb, ExchangeExchange, , Linear independenceLinear independence

InactiveInactive (core) (core) U U [[KrKr],4f ],4f F 1s F 1s

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Embedded Cluster HamiltonianEmbedded Cluster Hamiltonian

Relativistic Cowan-Griffin-Wood-Boring Hartree-Fock Relativistic Cowan-Griffin-Wood-Boring Hartree-Fock all-electron all-electron atomicatomic calculations calculations

+ + Frozen core approximationFrozen core approximation

CoulomCoulombb

Exchange + scalar relativisticExchange + scalar relativistic Linear Linear independenceindependence

+ + AIMP recipe for representation of AIMP recipe for representation of

operatorsoperators

long-range long-range locallocallocallocal

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CoulomCoulombb



operatorsoperators

short-rangeshort-range

spectral spectral representatiorepresentatio

nn

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operatorsoperators

CoulomCoulombb


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Perfect crystal latticePerfect crystal latticeloop over loop over lattice ionslattice ions until convergence until convergence

perform a single embedded-ion calculation (SCF, perform a single embedded-ion calculation (SCF, CASSCF)CASSCF)produce its produce its embedding-AIMPembedding-AIMP out of its orbitals out of its orbitalsupdate the lattice embedding potentialsupdate the lattice embedding potentials

end loopend loop

SSelf-elf-Consistent onsistent EEmbedded mbedded IIon on calculationscalculations

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Spin-orbit coupling / electron correlationSpin-orbit coupling / electron correlation

Spin-orbit splittingsSpin-orbit splittings

depend on:depend on: spin-orbit couplingsspin-orbit couplings spin-free spectrumspin-free spectrum

which demand:which demand: small CI space small CI space PP large CI space large CI space GG

Use Use GG space for the space for the spin-free spectrumspin-free spectrumUse Use PP space for the space for the spin-orbit couplingsspin-orbit couplings

An aproximate decoupling ofAn aproximate decoupling of correlationcorrelation andand spin-orbitspin-orbit

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Spin-free state shifted HamiltonianSpin-free state shifted Hamiltonian

Use Use PP space for the space for the spin-orbit couplingsspin-orbit couplings

small CI space small CI space PP large CI space large CI space GG

Use Use GG space for the space for the spin-free spectrumspin-free spectrum

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Use Use PP space for the space for the spin-orbit couplingsspin-orbit couplings

small CI space small CI space PP large CI space large CI space GG

Use Use GG space for the space for the spin-free spectrumspin-free spectrum

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Use Use PP space for the space for the spin-orbit couplingsspin-orbit couplingsUse Use GG space for the space for the spin-free spectrumspin-free spectrum

– Codes:Codes:

MOLCASMOLCASCOLUMBUSCOLUMBUS

Björn O. Roos et al., Lund UniversityRuss M. Pitzer et al., Ohio State University

EPCISOEPCISO Valérie Vallet et al., Université de Lille

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– Cluster: Cluster: (AnL(AnL66))q-q-

Details of the calculationsDetails of the calculations EmbeddedEmbedded--cluster cluster (embedding AIMP (embedding AIMP for ionic solidsfor ionic solids))

spin-free: spin-free: CASSCFCASSCF//CASPT2CASPT2

EffectivEffective ce core ore ppotential otential (Cowan-Grif(Cowan-Griffin-Wood-Boring based fin-Wood-Boring based AIMP)AIMP)

spin-orbit: spin-orbit: sfss-SOCI [MRCI(S)]sfss-SOCI [MRCI(S)]

– Embedding Embedding potentials:potentials:~ 500 AIMPs ~ 500 AIMPs + 3000 point charges + 3000 point charges

atat experimental sitesexperimental sites so that E(R) is stableso that E(R) is stable

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– Core AIMPs:Core AIMPs:An: [Xe,4f] 5d,6s,6p, 5f,6d,7sAn: [Xe,4f] 5d,6s,6p, 5f,6d,7sCl: [Ne] 3s,3pCl: [Ne] 3s,3p

– Valence basis sets:Valence basis sets:An: (14s10p12d9f3g)/[6s4p5d4f1g]An: (14s10p12d9f3g)/[6s4p5d4f1g]Cl: (7s7p1d)/[3s4p1d]Cl: (7s7p1d)/[3s4p1d]

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– SA-CASSCF:SA-CASSCF: [5f,6d,7s][5f,6d,7s]NN

– MS-CASPT2:MS-CASPT2: An: 5dAn: 5d10106s6s226p6p6 6 [5f,6d,7s][5f,6d,7s]NN + 6 x Cl: 3s + 6 x Cl: 3s223p3p66

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– spin-free-state-shifted Spin-Orbit CI:spin-free-state-shifted Spin-Orbit CI:Wood-Boring spin-orbit operator scaled by 0.9Wood-Boring spin-orbit operator scaled by 0.9Basis of double-group adapted functionsBasis of double-group adapted functionsMRCI(S) CAS[5f,6d,7s]MRCI(S) CAS[5f,6d,7s]NN

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Results: type of resultsResults: type of results

Local structure (ground/excited Local structure (ground/excited states)states)

bond lengths, vibrational frequenciesbond lengths, vibrational frequencies

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Results: type of results Results: type of results Local structure (ground/excited Local structure (ground/excited states)states)

bond lengths, vibrational frequenciesbond lengths, vibrational frequenciesWave functions (and their analyses)Wave functions (and their analyses) bonding interactionsbonding interactions

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bond lengths, vibrational frequenciesbond lengths, vibrational frequenciesWave functions (and their analyses)Wave functions (and their analyses) bonding interactionsbonding interactionsAbsorption/emission spectraAbsorption/emission spectra

transition energies, transition moments, emission transition energies, transition moments, emission lifetimeslifetimes

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transition energies, transition moments, emission transition energies, transition moments, emission lifetimeslifetimesMechanisms of energy transferMechanisms of energy transfer

upconversion/quantum cutting mechanismsupconversion/quantum cutting mechanisms

Green-to-blue light upconversion in CsGreen-to-blue light upconversion in Cs22ZrClZrCl66: : UU4+4+

UU4+4+ impurities impurities

5f5f22 levels levels

UOUO222+2+ impurities impurities

5f5f116d6d11 levels levels

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upconversion/quantum cutting mechanismsupconversion/quantum cutting mechanismsPressure effectsPressure effects

CsCs22NaYClNaYCl66:Ce:Ce3+3+ under pressure under pressure

P=0P=25 kbar

f1

d(t2g)1

d(eg)1

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upconversion/quantum cutting mechanismsupconversion/quantum cutting mechanismsPressure effectsPressure effects

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Results: accuracies Results: accuracies (validation + applications)(validation + applications)

CeCe PrPr NdNd PmPm SmSm EuEu GdGd TbTb DyDy HoHo ErEr TmTm YbYb LuLuThTh PaPa UU NpNp PuPu AmAm CmCm BkBk CfCf EsEs FmFm MdMd NoNo LrLr

CsCs22NaYClNaYCl66

CsCs22ZrClZrCl66

CsCs22GeFGeF66

SrFSrF22

BaFBaF22

YAG YAG (Y(Y33AlAl55OO1212))

Bond distances presumably (no EXAFS available)0.01Å

Bond length changes very good(exceptions?)

Cs2ZrCl6:Pa4+

YAG:Ce3+

Vibrational frequencies

5% Ce3+,Pr3+,Sm2+,Pa4+

Electronic transitions 10% Ce3+,Pa4+,U3+,U4+

Pressure induced shiftsof electronic transitions semiquantitative Sm2+

Intensidades relativas semiquantitative Ce3+,U3+,U4+CsCaBrCsCaBr33

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UU4+ 4+ in fluoridesin fluorides

UU4+ 4+ 5f5f22, 5f, 5f116d6d1 1 manifolds manifolds ~90 excit~90 excited statesed states

fluorides fluorides large transparency windowlarge transparency window

● ● UV solid state laserUV solid state laser● ● Phosphor based on quantum cutting or cascade Phosphor based on quantum cutting or cascade luminescenceluminescence

PotentialityPotentiality as as

Results: a show case Results: a show case

Predicting the luminescence of a new material Predicting the luminescence of a new material + experimental & theoretical study+ experimental & theoretical study

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UV solid state laserUV solid state laser

Strong, broad, fast Strong, broad, fast 6d6d→→5f 5f

luminescenceluminescence

quantum cutting orquantum cutting orcascade cascade

luminescenceluminescence5f5f116d6d11 levelslevels

11SS00

YLiFYLiF44:U:U4+4+ YFYF33:U:U4+4+

Weak, slow, two-step 5fWeak, slow, two-step 5f→→5f5fluminescenceluminescence

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UV solid state laserUV solid state laserquantum cutting orquantum cutting or

cascade cascade luminescenceluminescence

UU4+4+ in Cs in Cs22GeGeFF66

•The electronic structure of the 5fThe electronic structure of the 5f22 manifold manifold •The 5fThe 5f1 1 6d6d11 manifold manifold

• Promote the synthesis and experimental studyPromote the synthesis and experimental study

• An unexpected 5fAn unexpected 5f1 1 7s7s1 1 manifold: U-trapped manifold: U-trapped excitonsexcitons

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CsCs22GeFGeF66:U:U4+4+, a potential quantum cutter or solid state , a potential quantum cutter or solid state laser ?laser ?

11SS00


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quantum cutting orquantum cutting orcascade luminescencecascade luminescence

5f5f116d6d11 levelslevels

11SS00

11SS00

33PP00


33HH44



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11SS00





UV solid state laserUV solid state laser

Strong, broad, fast Strong, broad, fast 6d6d→→5f luminescence5f luminescence


11SS00

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Miroslaw Karbowiak, University of Wroklaw

• • growth of Csgrowth of Cs22GeFGeF66:U:U4+4+ single crystals single crystals• • experimental absorption spectrum (7 experimental absorption spectrum (7 K)K)

• • broad, intense bands 37000 – broad, intense bands 37000 – 45000cm45000cm-1-1

• • no appreciable fine vibronic no appreciable fine vibronic structurestructure

• • most prominent at 38000 cmmost prominent at 38000 cm-1-1

Absorption spectrum.Absorption spectrum.

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• • Theoretical spectrumTheoretical spectrum

•• 2500cm2500cm-1 -1 too high too high (0.3 eV) (0.3 eV) (7 %)(7 %) •• Five 5fFive 5f116d6d11 origins: 1A origins: 1A1g1g → → iTiT1u1u ( i = 1,5) ( i = 1,5)


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•• Intensities:Intensities:+ most prominent band 1A+ most prominent band 1A1g1g → →

1T1T1u1u+ relative intensities ok, + relative intensities ok,

- except for 1A- except for 1A1g1g → → 2T2T1u1u

•• 2500cm2500cm-1 -1 too high too high (0.3 eV) (0.3 eV) (7 %)(7 %) •• Five 5fFive 5f116d6d11 origins: 1A origins: 1A1g1g → → iTiT1u1u ( i = 1,5) ( i = 1,5)

• • Theoretical spectrumTheoretical spectrum

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Emission spectrum.Emission spectrum.

1T1T1g1g

1T1T2g2g

2T2T1g1g, 2T, 2T2g2g

3T3T2g2g


5f5f116d6d11 levels levels1E1Euu

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Large Stokes shift: 6200 cmLarge Stokes shift: 6200 cm-1-1


1T1T1g1g

1T1T2g2g

2T2T1g1g, 2T, 2T2g2g

3T3T2g2g

1A1A1g1g

1E1Euu

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Spontaneous emission Spontaneous emission lifetime: lifetime:


Experiments underwayExperiments underway

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An unexpected 5fAn unexpected 5f117s7s11 manifold: U-trapped exciton? manifold: U-trapped exciton?

2.154, 2.154, 2.174,2.174, 2.21 2.21 Å Å 2.092.09

U(IV)• • Bond length Bond length ~~ U(V) U(V) clustercluster• • Very diffuse 7s Very diffuse 7s orbitalorbital• • Energy sensitive to basisEnergy sensitive to basis set delocalization set delocalization

U - trapped exciton ?

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An unexpected 5fAn unexpected 5f117s7s11 manifold: U-trapped exciton? manifold: U-trapped exciton?

Impurity-trapped excitonImpurity-trapped exciton

D. S. McClure, et al. D. S. McClure, et al. Phys. Rev. B, 32, 8465 (1985)Phys. Rev. B, 32, 8465 (1985)

SrFSrF22:Yb:Yb2+2+ anomalous emissionanomalous emission

““The excited state ... could be called an The excited state ... could be called an impurity-trapped impurity-trapped excitonexciton, since it consists of a, since it consists of a bound electron-hole pair bound electron-hole pair with with thethe hole localized on the impurity hole localized on the impurity and theand the electron on electron on nearby lattice sites...”nearby lattice sites...”

““The trappedThe trapped exciton geometry exciton geometry is probablyis probably that expected that expected forfor a trivalent impurity ion, a trivalent impurity ion, YbYb3+3+...” ...”

YbYb2+2+ → → YbYb3+ 3+ + 1e(Sr) very short bond + 1e(Sr) very short bond lengthlength localised hole delocalised localised hole delocalised

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7s MO 7s MO [5f[5f117s7s11-2-233AA2u2u (UF (UF66CsCs88))6+6+]]7s AO 7s AO [5f[5f117s7s11--33F UF U4+4+]]

AnalAnalysis of the wavefunctionsysis of the wavefunctions

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•• Hole localized Hole localized in the U(5f)in the U(5f)

• • ~~ U(V) bond length U(V) bond length

Diffuse orbitals Diffuse orbitals of Ln/An in solids of Ln/An in solids can lead tocan lead to impurity trapped excitonsimpurity trapped excitons

Microscopic description of Microscopic description of an impurity trapped an impurity trapped exciton exciton

•• Electronic densityElectronic density in the frontier of in the frontier of

the UFthe UF66 unit unit

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Wavefunction based Wavefunction based ab initioab initio embedded cluster calculations on embedded cluster calculations on LnLnq+q+ and An and Anq+q+ impurities in ionic hosts impurities in ionic hosts

– Reliable enough (complement experiments, predict)Reliable enough (complement experiments, predict)– Can be used to progress in the understanding ofCan be used to progress in the understanding of Advanced Nuclear Energy SystemsAdvanced Nuclear Energy Systems

ConclusionsConclusions

What is next ?What is next ?Nuclear fuel and nuclear wastes materialsNuclear fuel and nuclear wastes materials

– UOUO22 (experimental spectroscopy available) , PuO (experimental spectroscopy available) , PuO22

– diluted UOdiluted UO22/PuO/PuO22 mixtures UO mixtures UO22:Pu:Pu4+4+, PuO, PuO22:U:U4+4+

Transuranium systems (the fTransuranium systems (the f77 configuration) configuration)– CmCm3+3+ in Cs in Cs22NaYClNaYCl6 6 (experimental spectroscopy available)(experimental spectroscopy available)– and Amand Am2+2+ and Bk and Bk4+4+

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AcknowledgmentsAcknowledgments

Luis SeijoLuis Seijo Belén Ordejón Belén Ordejón Ana Muñoz José Luis PascualJosé Luis Pascual meme José GraciaJosé Gracia Fernando Ruipérez Fernando Ruipérez

on campus, UAM 2006on campus, UAM 2006

Goar SánchezGoar Sánchez

Noémi BarrosNoémi Barros

in La Sierra, Madrid 2007in La Sierra, Madrid 2007

http://www.uam.es/quimica/aimp/

http://www.uam.es/quimica/aimp/

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AcknowledgmentsAcknowledgments

• Miroslaw Karbowiak, Miroslaw Karbowiak, Faculty of Chemistry, University of Wroclaw, Wroclaw, Faculty of Chemistry, University of Wroclaw, Wroclaw, PolandPoland

• Norman Edelstein,Norman Edelstein, Lawrence Berkeley National Laboratory, Berkeley, Lawrence Berkeley National Laboratory, Berkeley, California, USACalifornia, USA

• Björn Roos, Rolandh Lindh,Björn Roos, Rolandh Lindh, (MOLCAS)(MOLCAS) Lund University, Lund, SwedenLund University, Lund, Sweden• Russell Pitzer, Russell Pitzer, (COLUMBUS) Ohio State University, Columbus, Ohio, USA(COLUMBUS) Ohio State University, Columbus, Ohio, USA• Valérie Vallet, Jean-Pierre Flament Valérie Vallet, Jean-Pierre Flament (EPCISO) Université de Lille, Lille, France(EPCISO) Université de Lille, Lille, France • Spanish Ministry of Education and Science, Spanish Ministry of Education and Science, DGI-BQU2002-01316,DGI-DGI-BQU2002-01316,DGI-

CTQ2005-08550. CTQ2005-08550.

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Structure, bonding, and spectroscopy Structure, bonding, and spectroscopy of actinides in crystals.of actinides in crystals.

A quantum chemical perspectiveA quantum chemical perspectiveUniversidad Autónoma de MadridUniversidad Autónoma de Madrid

Structure, bonding, and spectroscopy of actinides in crystals A quantum chemical perspective

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