LUMINESCENCE OF RE LUMINESCENCE OF RE

OVERSATURATED CRYSTALSOVERSATURATED CRYSTALS

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

Fluorides allows to modify propertiesScintillator phosphor storage dosimetry

Broad variety of crystal lattices

What is the RE doping optimum?

Motivation

LiCaAlFLiCaAlF66 / LiSrAlFLiSrAlF66

colquiriite LiBaFLiBaF33

perovskiteВаМВаМgFgF44

orthorhombicorthorhombicLiFLiF

cubicBaF2

fluorite

LiF – dosimeterKMgF3(Eu) – UV dosimeter

BaFBr(Eu) – screen phosphor

BaF2 – fast scintillator

LiBaF3(Ce)–

n/discriminator

CaF2(Eu) – scintillator

New phosphors M1-xRExF2+x (M=Ca, Sr, Ba)

Structure of fluoriteMF2 (М=Ca, Sr, Ba)

Fi VFc

{F12}

Defect cluster[RE6F36]

Supercluster{M8[RE6F68-69]}

RE3+-Fi¯ dipole dimer, trimer, etc.

M1-xRExF2+xREF3

phase

increase of RE3+ 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 Ba0.65Pr0.35 F2.35 Systems

Internal structure is not still clearbut single crystals are available

*)Rodnyi, Phys.Rev. (2005)

BaF2

BaF2–Pr (0.3 mol%) *)

BaF2–Pr (3 mol%) *)

BaF2–Pr (35 mol%)

BaF2–Pr (35mol%) Ba0.65Pr0.35 F2.35

RE oversaturated crystals

Which properties will dominates?

crystal a, ÅCaF2 5.46305(8)

CaF0.65Eu0.35F2.35 5.55382(8)

CaF0.65Pr0.35F2.35 5.61359(4)

SrF2 5.800

Sr0.65Pr0.35F2.355.81578(2)

BaF2 6.200

BaF0.65Pr0.35F2.35 6.03744(6)

Me1–xPrxF2+x

M= Ca,Sr,Ba 0.22 < x < 0.5

ion R, ÅCa2+ 1.26

Eu3+ 1.21

Pr3+ 1.28

Sr2+ 1.39

Ba2+ 1.56

F– 1.19

Me1–xPrxF2+x

MeF2–Pr PrF3

Fluorides phase structure, superlattice

Non coherent inclusions

nano phases

Gleiter, Acta Met. (2000)

Coherent inclusions

M2+

R3+

Sobolev, Crystallography (2003)

M1-xRxF2+x with R3+ to 40%

Fluorides phase structure, superlattice

Non coherent inclusions Coherent inclusions

nano phases

Coincidence lattice with R3+ content 42.86% (Ba4Yb3F17).

Other step is 15.38%

Sobolev, Crystallography (2003)

Model of non stoichiometric crystal with R3+ content 40%

Eu2+ Eu3+ 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–→Eu3+) transitions occur in range of 6.5-10.5 eV;

CaF2(Eu) phosphor Ca0.65Eu0.35 F2.35

Eu2+ emissionin CaF2(Eu)

Eu3+ emissionin Ca0.65Eu0.35 F2.35

CCD camera sensitivity

BaF2–Pr photon cascade emission

Cascade emission:

1 step: 1S0 → 1I6 (~400 нм)

2 step: 3P0 → 3H4 (~482 нм)

Second step only

Energy levels and Pr3+

transitions

(Rodnyi, Phys.Rev., 2005)

BaF0.65Pr0.35F2.35

Pr absorption in different hosts

Ca0.65Pr0.35F2.35

Sr0.65Pr0.35F2.35

Ba0.65Pr0.35F2.35

Absorption peaks structure is similar for different hosts

Clasters structure and Pr3+ excitation spectra

Excitation for em= 250 нм

1. CaF2–Pr (0.1%)

2. Ca0.65Pr0.35F2.35

Broad excitation spectra due to Pr3+

cluster structure and peaks overlapping

300K8K

Emission spectra, 8K

0 50 100 150

100

1000

Fig.5

Coun

ts

Time, ns

CaF2:Pr(35%); Em=402nm, Exc=5.79eV, T=300K CaF2:Pr(35%); Em=402nm, Exc=6.20eV, T=300K CaF2:Pr(35%); Em=402nm, Exc=6.78eV, T=300K CaF2:Pr(35%); Em=402nm, Exc=8.00eV, T=300K CaF2:Pr(35%); Em=402nm, Exc=9.18eV, T=300K

200 250 300 350 400 450 500 550 600 650 700 7500

50

100

3P

0

3F

4

3P

0

3F

2

3P

0

3H

6

3P

0

3H

5

3P03H

4

(c)

1 BaF2:Pr(35%), E=5.61eV, T=8K2 BaF2:Pr(35%), E=7.75eV, T=8K3 BaF2:Pr(35%), E=4.86eV, T=8K

Wavelength, nm

200 250 300 350 400 450 500 550 600 650 700 7500

50

100

150

1S

0

3F

4

1S

0

1G

4

1S

0

1D

2

1S01I

0

(a)

1 CaF2:Pr(35%), E=5.39eV, T=8K2 CaF2:Pr(35%), E=5.60eV, T=8K3 CaF2:Pr(35%), E=5.80eV, T=8K4 CaF2:Pr(35%), E=8.00eV, T=8K5 CaF2:Pr(35%), E=13.48eV, T=8K

I, a

rb.u

.

Fig.6Emission spectraT=8 K

200 250 300 350 400 450 500 550 600 650 700 7500

20

40

60

Ce3+d-f

Ce3+d-f

(b)1 SrF2:Pr(35%), E=5.04eV, T=8K2 SrF2:Pr(35%), E=5.47eV, T=8K3 SrF2:Pr(35%), E=5.85eV, T=8K4 SrF2:Pr(35%), E=7.95eV, T=8K5 SrF2:Pr(35%), E=6.89eV, T=8K6 SrF2:Pr(35%), E=13.48eV, T=8K

Ca0.65Pr0.35F2.35

Sr0.65Pr0.35F2.35

Ba0.65Pr0.35F2.35

Emission spectra (photoexcitation), 300K

Ca0.65Pr0.35F2.35

Sr0.65Pr0.35F2.35

Multi cluster structure

Decay curves for different cluster peak excitation

Ca0.65Pr0.35F2.35

– luminescence and glow curve

CaPrF223 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

SrPrF230 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.

BaPrF250 nm o< 1 ns 325 nm 1 =37 ns

480 nm 2 =101 ns and 3 =549 ns

Glow curve

PropertiesCrystal

CaF2 :0.1%Pr Ca0.65Pr0.35F2.35 PrF3

Structure Cubic fluorite Cubic fluorite

Lattice constant, Å 5.46305(8) 5.61359(4) 7.078 / 7.239

Coordination number 8 >8 9

X-ray emission 77K

5d–4f, UV1So-

1Io

3P0-3H4

233, 251, 272nm―482nm

233, 251, 272nm400 nm―

233, 251, 272nm400 nm―

Photoluminescence Pr3+

5d–4f1So-

1Io

3P0-3H4

233, 251, 272nm―482nm

233, 251, 272nm400 nm―

233, 251, 272nm400 nm―

Excitation of d f Pr3+ emission

C4v site 154, 218 154, 218223, 160 - 190

154, 218223, 160 - 190

Cluster

τ1 (5d–4f), ns

τ2 (1S0 –

1I6), ns

20 ~311330

~318430

Ca–Pr–F compound emission

Compound SrF2-0.2%Pr Sr0.65Pr0.35F2.35 PrF3

Structure fluoride fluoride

distorted

hexagonal

Lattice constant a, Å

5.7996 5.81578(2) 7.0787.239

Coordination number

8 >8 9

X-ray emission

5d–4f, UV1So-

1Io

3P0-3H4

233, 251, 272nm―482nm

233, 251, 272nm400nm482nm

233, 251, 272nm400 nm―

Photoluminescence

5d–4f, UV1So-

1Io

3P0-3H4

233, 251, 272nm―482nm

233, 251, 272nm400 nm482nm

233, 251, 272nm400 nm―

Excitation of d f, nm

single Pr3+ 154, 218 154, 218 154, 218

cluster ― 223, 160 −190 223, 160-190

Decay time

1, (5d–4f)

2, (1So-

1Io)

2, (3P0-

3H4)

25―

< 534140

3, 18430―

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

CaF2:Pr 0.2% Ca0.65Pr0.35F2.35

Conclusions

1. Me1–xRExF2+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 Me0.65Pr0.35F2.35 compound but yield is still very low

4. Is it possible to make the same lattice with F substitution by Cl, Br or I ?