Growth of garnet and perovskite

scintillators with non-isovalent minor

components and related effects

A. Petrosyan1, K. Hovhannesyan1, M. Derdzyan1,

A. Yeganyan1, R. Sargsyan1, F. Moretti2, C. Dujardin2

1Institute for Physical Research, National Academy of Sciences, 0203 Ashtarak, Armenia

2Institut Lumière Matière, UMR 5306 Université Lyon 1-CNRS, Villeurbanne,

France

Co-doping Ce-materials with divalent impurities to stabilize Ce4+

S. Blahuta, et al, IEEE Trans. Nucl. Sci., 2013; LYSO:Ce,Ca(Mg) - Czochralski

M. Nikl, et al, Cryst. Growth & Design, 2014; LuAG:Ce,Mg - micro-pulling

Due to addition of divalent impurities, a partial oxidation of Ce3+ into Ce4+ takes place. What are advantages of Ce4+? ∙ Ce4+ can be considered as a pre-prepared Ce3+ which has already trapped a hole. This avoids the delays in hole trapping prior to electron trapping in the case of Ce3+. ∙ The result is acceleration of the decay and suppression

of long decay components. Can the divalent co-doping approach be useful for

materials other than silicates and garnets? Can co-doping with monovalent impurities be applied to

stabilize Ce4+?

Radiation hardness

Induced absorption for Ca and Mg

co-doped crystals (1 kGy).

500 550 600 650 700 750

0

1

2

3

4

5

6

3

2

ind,

m-1

nm

1

b1 LuAG:Ce, Mg

2 LuAG:Ce, Ca

3 LuAG:Ce

A.G. Petrosyan, et al, J. Cryst. Growth, 2015; LuAG:Ce,Ca

F. Moretti, et al, SCINT 2015; LuAG:Ce,Ca(Mg)

0.05 0.10 0.15 0.20 0.25

0

20

40

60

80

100

120

140

160

180

200

Ce, at%

ind,

m-1

b

Variation of induced absorption at 620 nm

with Ce concentration (Ca=100 ppm)

In addition, the fact that Ce4+ competes with other traps for electrons, Ca(Mg) co-doping improves the radiation hardness, if a proper balance

between Ce and co-dopant concentrations is optimized

Contents: materials and characterization

• Can the divalent co-doping approach be useful for materials other than silicates and garnets?

• Can co-doping with monovalent impurities be applied to stabilize Ce4+?

• YAP : Ce, Ca

• YAG : Ce with Li+ and Na+

• Crystal chemistry and substitution

• Defects (examples for LuAG:Ce,Ca(Mg)

• Absorption

• Annealing effects

• Compositions which can be readily grown as quality single crystals

Perovskite single crystals with Ca co-doping

• Czochralski YAlO3: Ce,Ca - (1) [Ce]= 1 at% (in the melt), [Ca]= 0, 100, 300, 500 ppm - (2) [Ce]= 100 ppm (in the melt), [Ca]= 0, 100, 300, 500 ppm

No degradation of crystalline quality is observed for introduced concentrations of Ca, so that single crystals can be grown under conditions usually applied to

YAP:Ce

YAP : Ce,Ca

200 300 400 500 600 700 8000

10

20

30

40

50

60

70

80

90

100

Wavelength /nm

Tra

nsm

issio

n /%

YAP:Ce 100 ppm

YAP:Ce 100 ppm, Ca 100 ppm

YAP:Ce 100 ppm, Ca 200 ppm

YAP:Ce 100 ppm, Ca 300 ppm

YAP:Ce 100 ppm, Ca 500 ppm

d= 2 mm

Transmission of YAP:Ce,Ca series

Decay is accelerated with increasing Ca concentration, which is a positive effect. The radioluminescence intensity is however decreased; among the reasons is

the degrading transmission in the range of emission (300-450 nm).

Similar effects were recorded in LuAP:Ce,Ca

F. Moretti , et al, ICDIM 2016

Time (ns)

0 50 100 150 200 250

Norm

aliz

ed a

mplit

ude

0.001

0.01

0.1

1Pulsed X-rays

em= 360 nm[Ca]= 0 ppm

[Ca]= 500 ppm

[Ca]= 100 ppm

[Ca]= 300 ppm

Decay

Garnet single crystals

*)K. Hovhannesyan, et al, ICDIM 2016

Vertical Bridgman method; tested compositions: (1) LuAG:Ce,Ca (Ce = 0.5-1 at%; Ca = 50 - 300 ppm)* (2) LuAG:Ce,Mg (Ce = 0.5–1 at%; Mg = 50–150 ppm) (3) YAG:Ce,Ca (Ce = 0.5 - 1 at% ; Ca = 200 ppm) (4) YAG:Ce,Li (Ce = 0.7 at% ; Li = 30 – 420 ppm) (5) YAG:Ce,Na (Ce = 0.7 at% ; Na = 70 ppm)

YAG:Ce,Na 70 ppm

YAG:Ce, Li 70-400 ppm

YAG:Ce,Ca

LuAG:Ce,Ca

LuAG:Ce,Mg

Melt compositions for quality crystals

• YAP: Ce, Ca - Ce ≤ 1%, Ca ≤ 500 ppm

• LuAP: Ce, Ca - Ce ≤ 0.5%, Ca ≤ 100 ppm

• LuAG: Ce, Ca - Ce ≤ 0.8 %, Ca ≤ 150 ppm

• LuAG: Ce, Mg - Ce ≤ 0.8 %, Mg ≤ 150 ppm

• YAG: Ce, Ca - Ce ≤ 1 %, Ca ≤ 200 ppm

• YAG:Ce, Li - Ce ≤ 1 %, Li ≤ 420 ppm

• YAG: Ce, Na - Ce ≤ 0.7 %, Na ≤ 70 ppm

Defects in LuAG:Ce,Ca

Ca = 0 Ca = 100 ppm Ca = 250 ppm Ca = 300 ppm

Longitudinal cuts under polarized light

Defects

LuAG:Ce,Ca100 ppm, Mg 60 ppm

Microphotographs obtained by the detector back-scattered electrons.

Microanalysis performed on the scanning electron microscope (SEM) VEGATS

5130MM with the system INCA Energy 300 of EDS microanalysis.

The concentration of Ce is non-homogeneous, increasing in dark spots

LuAG:Ce, Mg 150 ppm

Annealing effects

Oxidizing annealing is efficient to increase the concentration of Ce4+ , so that lower amounts of 2+ co-dopants can be introduced

LuAG: Ce, Ca

0 250 500 750 10001E-3

0,01

0,1

1

Am

plit

ud

e (

norm

aliz

ed)

Time (ns)

LuAG:Ce, Ca as-grown

annealed (air 1600o C, 10 h)

b

200 300 400 500 600 7000

2000

4000

6000

LuAG:Ce, Ca

as-grown

annealed (air 1600o

C, 10 hour)

RL

am

plit

ud

e (

arb

.un

its)

Wavelength (nm)200 300 400 500 600 700 8000

20

40

60

80

100

120

140

160

180

a

1 as-grown, Ce3+ - 0.14 at%

2 oxidized, Ce3+ - 0.127 at%

3 reduced, Ce3+ - 0.132 at%

nm

k, cm

-1

1

2

3

Li and Na in garnets

Li+ : a and d sites

{Ca3} [Li M2+] (V3) O12 M=Mg, Co, Ni, Cu, Zn - Vanadates

with garnet structure (G. Bayer, 1965)

{Na3} [Al2] (Li3) F12 – cryolithionite (G. Menzer, 1930)

Na+ : c sites

{NaCa2} [Mn2] (As3) O12 - berzelit (F. Machatschki, 1930)

{Na3} [Al2] (P3) O12 - (E. Thilo, 1941)

----------------------- YAG:Nd,Li - P. Arsenev, et al, phys. stat. sol (a) 1973

LuAG:Ce,Li - K. Kamada, M. Nikl, et al, J, Crystal Growth 2016

(accepted paper)

X-ray diffraction in YAG:Ce with Li co-doping

Ceramic samples 1600 C, air

Single phase garnet structure is conserved in YAG:Li and YAG:Ce,Li even at very high Li concentrations (1750 ppm).

Lattice parameters of YAG:Li and YAG:Ce,Li

Li+ - 0.92 Å (8); 0.76 Å (6). Y3+ - 1.02 Å (8). Al3+ – 0.53 Å (6)

Most of Li+ probably goes to interstitial positions

YAG:Ce, Li single crystals

500 600 700010002000RL amplitude (a.u.) Wavelength (nm) YAG:Ce(0.26%) YAG:Ce(0.27%), Li(35 ppm) YAG:Ce(0.26%), Li(70 ppm) YAG:Ce(0.295%), Li(400 ppm)200 400 600 800 1000020406080100Transmission, % YAG:Ce, Li (400 ppm) 0.176% Ce 0.295% CeWavelength nm

YAG:Ce,Li 35ppm; YAG:Ce, Li 70ppm; YAG:Ce,Li 400 ppm

200 300 4000

10

20

30

40 YAG:Ce(0,176%),Li(400 ppm)

YAG:Ce(0.177 at%)

Wavelength nm

Ab

so

rptio

n c

oe

ffic

ien

t, c

m-1

200 400 600 800 10000

20

40

60

80

100

Tra

nsm

issio

n,

%

YAG:Ce, Li (400 ppm)

0.176% Ce

0.295% Ce

Wavelength nm

500 600 7000

1000

2000

RL

am

plit

ud

e (

a.u

.)

Wavelength (nm)

YAG:Ce(0.26%)

YAG:Ce(0.27%), Li(35 ppm)

YAG:Ce(0.26%), Li(70 ppm)

YAG:Ce(0.295%), Li(400 ppm)

500 600700010002000RL amplitude (a.u.)Wavelength (nm) YAG:Ce(0.26%) YAG:Ce(0.27%), Li(35 ppm) YAG:Ce(0.26%), Li(70 ppm) YAG:Ce(0.295%), Li(400 ppm)2004006008001000020406080100Transmission, %YAG:Ce, Li (400 ppm) 0.176% Ce 0.295% CeWavelengthnm

Co-doping of YAG:Ce with Na+

200 300 400 500 600 700 800020406080100120 YAG:Ce, Na(70 ppm) 0.1% Ce 0.12% Ce 0.15% Ce YAG:Ce(0.176%), Li 400 ppm YAG:Ce(0.177%)Absorption coefficient, cm-1 Wavelength nm

Absorption in UV in Na co-doped crystals is high, comparable to those in Ca or Mg co-doped.

Na+ is efficient to stabilize Ce4+ states

200 250 3000

20

40

60

80

200 400 600 8000

20

40

60

80

100

120

Wavelength nm

YAG:Ce, Na(70 ppm)

0.1% Ce

0.12% Ce

0.15% Ce

YAG:Ce

0.107% Ce

0.12% Ce

0.163% Ce

Ab

so

rptio

n c

oe

ffic

ien

t, c

m-1

Wavelength nm

Diff. a

bs. co

effic

ien

t, c

m-1

252 nm

200 300 400 500 600 700 8000

20

40

60

80

100

120YAG:Ce, Na(70 ppm)

0.1% Ce

0.12% Ce

0.15% Ce

YAG:Ce(0.176%), Li 400 ppm

YAG:Ce(0.177%)

Ab

so

rptio

n c

oe

ffic

ien

t, c

m-1

Wavelength nm

200300400500600700800020406080100120YAG:Ce, Na(70 ppm) 0.1% Ce 0.12% Ce 0.15% Ce YAG:Ce(0.176%), Li 400 ppm YAG:Ce(0.177%)Absorption coefficient, cm-1Wavelengthnm

Summary

• The maximum concentrations of additional divalent or monovalent impurities that can be introduced, while conserving high quality of single crystals, were determined in different hosts .

• Oxidizing annealing of garnets is efficient to additionally increase the concentration of Ce4+.

• Co-doping of YAP with Ca leads to acceleration of the decay, however the emission intensity is decreased.

• Introduction of Li+ into YAG:Ce does not lead to formation of Ce4+ states. Basing on lattice parameters, it is suggested that Li+ goes to interstitial positions.

• Na+ is efficient to stabilize Ce4+ states in YAG:Ce single crystals.

Thank you for your attention

This work has been performed in the framework of

International Associated Laboratory IRMAS

(CNRS-France and SCS-Armenia)

and

EU H2020 programme grant n. 644260

(INTELUM)

Experimental (ILM – CNRS)

Radioluminescence spectra were recorded at RT under X-ray

irradiation. The excitation source was X-ray tube (Philips 2274)

operated at 30 kV, 20 mA, exposure time is 5 seconds.

Monochromator working in the range 430-770 nm and 230-570 nm

for YAG:Ce,Li(Ca) and LuAG:Pr,Ca respectively.

Scintillation decay measurements were performed at room

temperature under X-ray excitation using a picosecond pulsed laser

(C10196; Hamamatsu Inc.) with 100 kHz and 0.2 mA, using

interference filters YG11 and 320BP10 for YAG:Ce,Li(Ca) and

LuAG:Pr,Ca respectively. To analyze the temporal histogram for the

counts TCSPC module (PicoHarp 300) is adopted.