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LUMINESCENCE OF RE OVERSATURATED CRYSTALS

A . Gektin a * , N . Shiran a , V . Nesterkina a , G. Stryganyuk b , K. Shimamura c , E. Víllora c , K . Kitamura c a Institute for Scintillation Materials, NAS of Ukraine, Kharkov b HASYLAB at Deutsches Elektronensynchrotron DESY , Hamburg , Germany

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LUMINESCENCE OF RE OVERSATURATED CRYSTALS

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  1. A. Gektina*, N. Shirana, V. Nesterkinaa, G. Stryganyukb, K. Shimamurac, E. Víllorac, K. Kitamurac aInstitute for Scintillation Materials, NAS of Ukraine, Kharkov bHASYLAB at Deutsches Elektronensynchrotron DESY, Hamburg, Germany cAdvanced Materials Lab., Nat. Inst. for Materials Science, Tsukuba, Japan LUMINESCENCE OF RE OVERSATURATED CRYSTALS

  2. LiFcubic ВаМgF4 orthorhombic LiBaF3perovskite BaF2 fluorite LiCaAlF6/LiSrAlF6 colquiriite Motivation • LiF – dosimeter • KMgF3(Eu) – UV dosimeter • BaFBr(Eu) – screen phosphor • BaF2 – fast scintillator • LiBaF3(Ce)– n/g discriminator • CaF2(Eu) – scintillator • Fluorides allows to modify properties Scintillator  phosphor  storage  dosimetry • Broad variety of crystal lattices • What is the RE doping optimum?

  3. It is supposed that defect clusters and fluoride phases of non-stoichiometric crystals can form nanostructures that opens an possibility to engineering materials with various kinds of properties. M1-xRExF2+x dimer, trimer, etc. REF3 phase RE3+-Fi¯ dipole Fi VFc {F12} Structure offluorite MF2 (М=Ca, Sr, Ba) Defect cluster [RE6F36] Supercluster {M8[RE6F68-69]} New phosphorsM1-xRExF2+x (M=Ca,Sr,Ba) increase of RE3+ concentration in fluoridematrix detect clusters 20-50% ~0.1% ~1-2% ~3-5% ~10%

  4. Phase Diagrams of Ba0.65Pr0.35 F2.35 Systems BaF2 BaF2–Pr (0.3 mol%)*) BaF2–Pr (3 mol%)*) BaF2–Pr (35 mol%) BaF2–Pr (35mol%)  Ba0.65Pr0.35 F2.35 Internal structure is not still clear but single crystals are available *)Rodnyi, Phys.Rev. (2005)

  5. RE oversaturated crystals Me1–xPrxF2+x M= Ca,Sr,Ba 0.22 < x < 0.5 Me1–xPrxF2+x PrF3 MeF2–Pr Which properties will dominates?

  6. Fluorides phase structure, superlattice Non coherent inclusions Coherent inclusions M2+ R3+ nano phases M1-xRxF2+x with R3+ to 40% Gleiter, Acta Met. (2000) Sobolev, Crystallography (2003)

  7. Fluorides phase structure, superlattice Non coherent inclusions Coherent inclusions Coincidence lattice with R3+content 42.86% (Ba4Yb3F17). Other step is 15.38% nano phases Model of non stoichiometric crystal with R3+ content 40% Sobolev, Crystallography (2003)

  8. Eu2+ Eu3+ transformation by “lattice engineering” CaF2(Eu) phosphor Ca0.65Eu0.35 F2.35 Eu2+ emission in CaF2(Eu) Eu3+ emission in Ca0.65Eu0.35 F2.35 CCD camera sensitivity • At energies E < 6.5 eV only interconfigurational 4f-4f transitions are observed; • Intraconfigurational 4f-5d and charge transfer (F–→Eu3+)transitionsoccur in rangeof 6.5-10.5 eV;

  9. Secondstep only BaF2–Pr photon cascade emission Cascade emission: 1 step:1S0 → 1I6 (~400 нм) 2step: 3P0 → 3H4 (~482 нм) Energy levels and Pr3+transitions BaF0.65Pr0.35F2.35 (Rodnyi, Phys.Rev., 2005)

  10. Ca0.65Pr0.35F2.35 Sr0.65Pr0.35F2.35 Ba0.65Pr0.35F2.35 Pr absorption in different hosts • Absorption peaks structure is similar for different hosts

  11. 300K 8K Clastersstructure and Pr3+ excitation spectra Excitation for lem= 250 нм • CaF2–Pr (0.1%) • Ca0.65Pr0.35F2.35 • Broad excitation spectra due to Pr3+cluster structure and peaks overlapping

  12. Hexagonal, space group Emission spectra, 8K Ca0.65Pr0.35F2.35 Sr0.65Pr0.35F2.35 Ba0.65Pr0.35F2.35

  13. Emission spectra (photoexcitation), 300K Ca0.65Pr0.35F2.35 Sr0.65Pr0.35F2.35

  14. Multi cluster structure Decay curves for different cluster peak excitation Ca0.65Pr0.35F2.35

  15. g –luminescence and glow curve CaPrF 223 nmto< 5 ns, 250 nm t1 =25 nsandt2 =262 ns 273 nm t1 =54 nsandt2 =300 ns 400 nm t1 =71 nsandt=330 ns SrPrF 230 and 275 nm to <5 ns 325 nm t1 =35 ns 400 nm t1 =34 ns 475 nm t1 =23 нс andt2 =139 ns. BaPrF 250 nm to< 1 ns 325 nm t1 =37 ns 480 nm t2 =101 nsand t3 =549 ns Glow curve

  16. Hexagonal, space group Ca–Pr–F compound emission

  17. Sr–Pr–F compound emission

  18. CaF2:Pr 0.2% Ca0.65Pr0.35F2.35 Photon cascade conditions • S level should be separated from f-d level • Minimal influence of cross relaxation This has to corresponds to: * coordination number more then 8-9 * large distance between Pr and anion ions

  19. Conclusions • Me1–xRExF2+x – is a stable crystal lattice with RE content to 50% • RE ions aggregation gives a lot of clasters • Photon cascade emission is typical for all Me0.65Pr0.35F2.35 compound but yield is still very low • Is it possible to make the same lattice with F substitution by Cl, Br or I ?

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