Scintillation Mechanism in Complex Structure Doped Oxides and Novel Developments M.Korzhik. Institute for Nuclear Problems, Minsk, Belarus

Transcription

1 Scintillation Mechanism in Complex Structure Doped Oxides and Novel Developments M.Korzhik Institute for Nuclear Problems, Minsk, Belarus

2 SCINTILLATION MECHANISM IN OXIDE COMPOUNDS The bright scintillation occurs in Ce 3+ doped oxide crystals, (1) when conditions for autolocalization of holes and excitons exist in the crystalline matrix; (2) when undoped crystal have an intrinsic excitonic and recombination luminescence from relaxed excited states; (3) when crystals doped with Ce 3+ have a reasonable overlapping of the intrinsic matrix luminescence bands and the activator absorption interconfiguration bands.

3 THE MOST IMPORTANT MECHANISMS OF EXCITATION TRANSFER I. Energy transfer mechanism e+h +Се 3+ STE+Се 3+ (Се 3+ )*, e+h +Се 3+ STH+Се 3+ (Се 3+ )*, II. Charge transfer mechanism e+h+ Се 3+ STH + Се 3+ Се 4+ +е (Се 3+ )*, e+h+ Се 3+ Се 4+ +е (Се 3+ )*.

4 AUTOLOCALIZATION OF ELECTRONS, HOLES AND EXCITONS IN OXIDE COMPOUNDS Crystals on a base of polyhedra SiO 4 SiO 6, AlO 4, AlO 6, BO3, BeO 4,GaO 6,GaO 4. I. s- orbitals Conducting zone II. 2p-orbitals ( ) t, t ( ). 1g π 1u π Valent zone I. 2p oxygen orbitals at the top of valence band-a necessary conditions for hole autolocalization II. s orbital localization at the bottom part of conducting band a necessary condition for exciton autolocalization.

5 HOW TO CONSTRUCT HEAVY COMPOUNDS IN CASE OF OXIDES? EXAMPLE: ISOVALENT SUBSTITUTION OF THE MATRIX ION BY Ce 3+ ION Valent state of the first cation M Valent state of the second cation N MNX 3 M 3 N M 2 NX 5 M 2 N 2 X 7 M 2 N 3 X 9 M 4 N 3 X M 3 NX 7 MN 3 X 9 M 4 N 2 X 11 M 3 N 3 X 12 Compound formula

6 PHASE AND CHEMICAL STABILITY LIMITATION Valent state of the first cation M Valent state of the second cation N MNX 3 M 3 N M 2 NX 5 M 2 N 2 X 7 M 2 N 3 X 9 M 4 N 3 X M 3 NX 7 MN 3 X 9 M 4 N 2 X 11 M 3 N 3 X 12 Compound formula

7 Gd BASED COMPOUNDS Firs cation Second cation Compound formula M N Gd 3+ Al 3+ Gd AlO 3 Gd 3Al Si 4+, Ge 4+, Sn 4+ Gd 2SiO 5, Gd 2GeO 5, Gd 2SnO 5 Gd 2Si 2 O 7, Gd 2Ge 2 O 7, Gd 2Sn 2 O 7 Gd 2Si 3 O 9, Gd 2Ge 3 O 9, Gd 2Sn 3 O 9 Gd 4 Si 3 O 12, Gd 4 Ge 3 O 12, Gd 4 Sn 3 O 12 Zr 5+, Hf 5+ Gd 3ZrO 7, Gd 3HfO 7 Gd Zr 3 O 9, Gd Hf 3 O 9 Gd 4Zr 2 O 11, Gd 4Hf 2 O 11 Gd 3Zr 3 O 12, Gd 3Hf 3 O 12

8 Lu BASED COMPOUNDS Firs cation Second cation Compound formula M N Lu 3+ Al 3+ LuAlO 3 Lu 3 Al Si 4+, Ge 4+, Sn 4+ Lu 2 SiO 5, Lu 2 GeO 5, Lu 2 SnO 5 Lu 2 Si 2 O 7, Lu 2 Ge 2 O 7, Lu 2 Sn 2 O 7 Lu 2 Si 3 O 9, Lu 2 Ge 3 O 9, Lu 2 Sn 3 O 9 Lu 4 Si 3 O 12, Lu 4 Ge 3 O 12, Lu 4 Sn 3 O 12 Zr 5+, Hf 5+ Lu 3 ZrO 7, Lu 3 HfO 7 LuZr 3 O 9, LuHf 3 O 9 Lu 4 Zr 2 O 11, Lu 4 Hf 2 O 11 Lu 3 Zr 3 O 12, Lu 3 Hf 3 O 12

9 THREE AND MORE CATIONS compounds MNKO compounds MN 2 K 2 O compounds MN 4 K 2 X 11. DRAWBACK DECREASE OF THE COMPOUND COMPACTNESS AND DENSITY DECREASE OF THE BAND GAP

10 INTRINSIC LUMINESCENCE OF DIFFERENT OXIDE COMPOUNDS VERSUS ENERGY GAP 500 CdWO 4 BGO 4 BSO 450 CaWO 4 PbWO λ, nm YTaO 4 YSO LSO YAG YAG LuAP YAP 250 YAP Energy gap, ev

11 INTRINSIC LUMINENSCENCE AND AVERAGE d-f Ce 3+ ION CONFIGURATION SPLITTING IN OXIDES 500 CdWO 4 BGO 4 BSO 450 CaWO 4 PbWO λ, nm YTaO 4 YSO LSO YAG YAG LuAP YAP 250 YAP Energy gap, ev Ce 3+ E d-e E gap Ce 3+ E d-e E gap

12 OBJECTS FOR INVESTIGATION COMPOUNDS & STRUCTURE OXYORTHO- GARNET PIROCHLOR PEROVSKITE 3+4+ Gd 2 GeO 5 :Ce La 2 Sn 2 O 7 :Ce Y 2 Sn 2 O 7 :Ce Lu 2 Sn 2 O 7 :Ce 2+4+ CaSnO 3 :Ce SrSnO 3 :Ce Ca 3 Lu 2 (GeO 4 ) 3 :Ce

13 Gd 2 GeO 5 :Ce. Luminescence and excitation spectra,1-λ exc =380nm, 2-λ exc =300 nm, 3-λ exc =360 nm, 4-λ lum =460 nm, 5- λ lum =520nm,T=300K Intensity, counts Wavelength, nm

14 Ca 3 Lu 2 (GeO 4 ) 3 :Ce. Luminescence and excitation spectra, 1-λ exc =325 nm, 2-λ exc =370 nm, the low intensity luminescence band-λ exc =280 nm, 3-λ lum =500 nm, 4-λ lum =420 nm, 5-λ lum =460nm Intensity, counts Wavelenth, nm

15 DRAWBACK OF Ge-RE COMPOUNDS THERMOIONIZATION OF Ce 3+ Gd 2 SiO 5 Gd 2 GeO 5 d f Ce 3+

16 Luminescent Properties of Several Sn 4+ (6) based compounds doped with Ce 3+ COMPOUND λ 1, nm λ 2, nm λ exc, nm Y 2 Sn 2 O La 2 Sn 2 O Lu 2 Sn 2 O CaSnO 3 412, 455 SrSnO 3 415, very weak 330, , , , , ,335,358, , 320, , ,330,353, , , 325, 385

17 Lu 2 Sn 2 O 7 :Ce. Luminescence and excitation spectra, 1-λ exc =325 nm, 2-λ exc =370 nm, 3-λ lum =500 nm, 4-λ lum =500 nm, 5-λ lum =640nm, T=300K Intensity, counts Wavelength, nm

18 Sn 4+ (4) BASED COMPOUNDS NEW CONPOUNDS DRAWBACK-NOT HEAVY MATERIALS PARTIAL SUBSTITUTION OF Si BY Sn AND Ge DRAWBACK - A LARGE DIFFERENCE BETWEEN ION RADIAI IN OXYGEN TETRAHEDRA Si A, Ge A, Sn 4+ -(0.61A) PARTIAL SUBSTITUTION OF Si BY Ge OR Sn IN LSO.

19 Lu 2 (Si-Ge) 2 O 5 (LSGO) AND Lu 2 (Si-Sn) 2 O 5 (LSSO) CRYSTALS Radioluminescence spectra of LSSO(1), LSGO (2) and reference LSO (3) crystals doped with Ce 3+, T=300K Norm. intensity Wavelenghth, nm

20 LSSO:Ce. Luminescence and excitation spectra of crystal with replacement of 10% Si by Sn in the raw material, 1-λ exc =350 nm, 2-λ exc =325 nm, 3-λ exc =310 nm, 4-λ exc =375 nm, 5-λ lum =450 nm, 6-λ lum =400 nm, 7-λ lum =500 nm, 8-λ lum =550 nm, T=300K Ce 3+ (6) Sn 2+ (6) Intensity, counts Wavelength, nm

21 ENERGY TRANSFER IN LSSO:Ce Ce 3+ (6) Sn 2+ (6) fast decay slow decay MIGRATION AND PRIMARY RADIATION RELAXATION OF Ce 3+

22 LSSO (1) and LSGO (2). Scintillation kinetics of crystals doped with Ce at concentration 1 at.% in raw material, T=300K. 1 1 Norm. intensity Time, ns Room temperature light yield of first samples of LSSO and LSGO is found to be and ph/mev correspondingly.

23 CONCLUSIONS Spectroscopic and scintillation properties of several Ge and Sn based oxide compounds have been investigated. Further progress for Ge based oxide materials is strongly dependent on the overcoming of the problem of Ge evaporation in the temperature range C. Partial substitution of Si by Sn in oxyorthosilicates looks promising to construct heavy and fast scintillators with high light yield. Combination of LSO/LSSO scintillators opens good prospects to construct PET scanners phoswich detectors with DOI capability