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 c Advanced Materials Lab., Nat. Inst. for Materials Science, Tsukuba, Japan

 Fluorides allows to modify properties Scintillator  phosphor  storage  dosimetry  Broad variety of crystal lattices  What is the RE doping optimum? Motivation LiCaAlF 6 LiSrAlF 6 LiCaAlF 6 / LiSrAlF 6 colquiriite LiBaF 3 LiBaF 3 perovskite ВаМgF 4 orthorhombic LiF LiF cubic BaF 2 fluorite  LiF – dosimeter  KMgF 3 (Eu) –UV dosimeter  BaFBr(Eu) – screen phosphor  BaF 2 – fast scintillator  LiBaF 3 (Ce)– n/  discriminator  CaF 2 (Eu) – scintillator

New phosphors M 1-x RE x F 2+x (M=Ca, Sr, Ba) Structure of fluorite MF 2 (М=Ca, Sr, Ba) FiFi V Fc {F 12 } Defect cluster [RE 6 F 36 ] Supercluster {M 8 [RE 6 F ]} RE 3+ -F i ¯ dipole dimer, trimer, etc. M 1-x RE x F 2+x REF 3 phase increase of RE 3+ concentration in fluoride matrix 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. detect clusters ~0.1%~1-2%~3-5%~10% 20-50%

Phase Diagrams of Ba 0.65 Pr 0.35 F 2.35 Systems Internal structure is not still clear but single crystals are available *)Rodnyi, Phys.Rev. (2005) BaF 2 BaF 2 –Pr (0.3 mol%) *) BaF 2 –Pr (3 mol%) *) BaF 2 –Pr (35 mol%) BaF 2 –Pr (35mol%)  Ba 0.65 Pr 0.35 F 2.35

RE oversaturated crystals Which properties will dominates? crystala, Å CaF (8) CaF 0.65 Eu 0.35 F (8) CaF 0.65 Pr 0.35 F (4) SrF Sr 0.65 Pr 0.35 F (2) BaF BaF 0.65 Pr 0.35 F (6) Me 1–x Pr x F 2+x M= Ca,Sr,Ba 0.22 < x < 0.5 ionR, Å Ca Eu Pr Sr Ba F–F– 1.19 Me 1–x Pr x F 2+x MeF 2 –Pr PrF 3

Fluorides phase structure, superlattice Non coherent inclusions nano phases Gleiter, Acta Met. (2000) Coherent inclusions M 2+ R 3+ Sobolev, Crystallography (2003) M 1-x R x F 2+x with R 3+ to 40%

Fluorides phase structure, superlattice Non coherent inclusions Coherent inclusions nano phases Coincidence lattice with R 3+ content 42.86% (Ba 4 Yb 3 F 17 ). Other step is 15.38% Sobolev, Crystallography (2003) Model of non stoichiometric crystal with R 3+ content 40%

Eu 2+  Eu 3+ transformation by “lattice engineering” 1. At energies E < 6.5 eV only interconfigurational 4f-4f transitions are observed; 2. Intraconfigurational 4f-5d and charge transfer (F – →Eu 3+ ) transitions occur in range of eV; CaF 2 (Eu) phosphor  Ca 0.65 Eu 0.35 F 2.35 Eu 2+ emission in CaF 2 (Eu) Eu 3+ emission in Ca 0.65 Eu 0.35 F 2.35 CCD camera sensitivity

BaF 2 –Pr photon cascade emission Cascade emission: 1 step: 1 S 0 → 1 I 6 (~400 нм) 2 step: 3 P 0 → 3 H 4 (~482 нм) Second step only Energy levels and Pr 3+ transitions (Rodnyi, Phys.Rev., 2005) BaF 0.65 Pr 0.35 F 2.35

Pr absorption in different hosts Ca 0.65 Pr 0.35 F 2.35 Sr 0.65 Pr 0.35 F 2.35 Ba 0.65 Pr 0.35 F 2.35  Absorption peaks structure is similar for different hosts

Clasters structure and Pr 3+ excitation spectra Excitation for em = 250 нм 1. CaF 2 –Pr (0.1%) 2. Ca 0.65 Pr 0.35 F 2.35  Broad excitation spectra due to Pr 3+ cluster structure and peaks overlapping 300K 8K

Hexagonal, space group Emission spectra, 8K Ca 0.65 Pr 0.35 F 2.35 Sr 0.65 Pr 0.35 F 2.35 Ba 0.65 Pr 0.35 F 2.35

Emission spectra (photoexcitation), 300K Ca 0.65 Pr 0.35 F 2.35 Sr 0.65 Pr 0.35 F 2.35

Multi cluster structure Decay curves for different cluster peak excitation Ca 0.65 Pr 0.35 F 2.35

 – luminescence and glow curve CaPrF 223 nm   o < 5 ns, 250 nm   1 =25 ns and  2 =262 ns 273 nm   1 =54 ns and  2 =300 ns 400 nm   1 =71 ns and  =330 ns SrPrF 230 and 275 nm   o <5 ns 325 nm   1 =35 ns 400 nm   1 =34 ns 475 nm   1 =23 нс and  2 =139 ns. BaPrF 250 nm   o < 1 ns 325 nm   1 =37 ns 480 nm   2 =101 ns and  3 =549 ns Glow curve

Hexagonal, space group Properties Crystal CaF 2 :0.1%PrCa 0.65 Pr 0.35 F 2.35 PrF 3 StructureCubic fluorite Lattice constant, Å (8) (4)7.078 / Coordination number 8>89 X-ray emission 77K 5d–4f, UV 1 S o - 1 I o 3 P H 4 233, 251, 272nm ― 482nm 233, 251, 272nm 400 nm ― 233, 251, 272nm 400 nm ― Photoluminescence Pr 3+ 5d–4f 1 S o - 1 I o 3 P H 4 233, 251, 272nm ― 482nm 233, 251, 272nm 400 nm ― 233, 251, 272nm 400 nm ― Excitation of d f Pr 3+ emission C 4v site154, , , , Cluster τ 1 (5d–4f), ns τ 2 ( 1 S 0 – 1 I 6 ), ns 20~ ~ Ca–Pr–F compound emission

CompoundSrF %PrSr 0.65 Pr 0.35 F 2.35 PrF 3 Structurefluoride distorted hexagonal Lattice constant a, Å (2) Coordination number 8>89 X-ray emission 5d–4f, UV 1 S o - 1 I o 3 P H 4 233, 251, 272nm ― 482nm 233, 251, 272nm 400nm 482nm 233, 251, 272nm 400 nm ― Photoluminescence 5d–4f, UV 1 S o - 1 I o 3 P H 4 233, 251, 272nm ― 482nm 233, 251, 272nm 400 nm 482nm 233, 251, 272nm 400 nm ― Excitation of d f, nm single Pr , 218 cluster―223, 160 −190223, Decay time  1, (5d–4f)  2, ( 1 S o - 1 I o )  2, ( 3 P H 4 ) 25 ― < , ― Sr–Pr–F compound emission

Photon cascade conditions 1. S level should be separated from f-d level 2. Minimal influence of cross relaxation This has to corresponds to: * coordination number more then 8-9 * large distance between Pr and anion ions CaF 2 :Pr 0.2% Ca 0.65 Pr 0.35 F 2.35

Conclusions 1. Me 1–x RE x F 2+x – is a stable crystal lattice with RE content to 50% 2. RE ions aggregation gives a lot of clasters 3. Photon cascade emission is typical for all Me 0.65 Pr 0.35 F 2.35 compound but yield is still very low 4. Is it possible to make the same lattice with F substitution by Cl, Br or I ?