energy transfer processes in ca tb si o :eu

Energy transfer processes in Ca3Tb2Si3O12:Eu3+

Irene Carrasco Ruiz Luminescent Materials Group. UNIVR Verona 2015

OUTLINE

Motivation

Sample details

Results: -RT luminescence experiments -8K-330K luminescence experiments Conclusions Future work

ICR. Luminescent Materials Lab. UNIVR LUMINET Meeting. Verona 2015

MOTIVATION


Rare earth phosphors are light-emitting materials with wide variety of applications.

Plasma display panels

White LEDs

Blue LED chip + yellow-emitting phosphor Cool light

Cool white Pure white Warm white

White LEDs: High brightness

Low energy consumption High reliability Long lifetime Eco-friendly

UV-LED chip + tricolor emitting phosphors Warm light

New phosphors to improve UV-excited white LEDs


Sensitization is a traditional way to enhance luminescence efficiency

Both ions exhibit absorption bands in the UV

Tb3+ is a very good sensitizer for Eu3+

Green emission from Tb3+ and red emission from Eu3+ have many applications in lighting and displays

Tb3+ - Eu3+ silico-carnotite materials are very interesting and promising for white LEDs

Silicate phosphors: Good transparency in UV-VIS

Favorable luminescent properties High chemical stability

Low cost

Silico-carnotite type structure: Orthorombic space group, Pnma Good stability for RE doping from

Eu-Lu ions

Study the Tb3+-Eu3+ energy transfer processes in Ca3Tb2Si3O12:Eu3+ .

OBJECTIVE

ICR. Luminescent Materials Lab. UNIVR

Performing luminescence and decay time experiments in Ca3Tb2Si3O12 , Ca3Tb2Si3O12:Eu3+

and in Ca3Eu2Si3O12 powders.

METHODOLOGY

LUMINET Meeting. Verona 2015

Ca3Tb2Si3O12,Ca3Eu2Si3O12 and Ca3Tb2Si3O12:Eu3+ (5 mol%)

Synthesized by SSR (III TT at 1450 oC x 3h)

Homogeneus white powders.Pure phase

SAMPLE DETAILS

20 30 40 50 60 70 80 90

X-r

ay d

iffr

acti

on

inte

nsit

y (

arb

. u

nit

s)

2(°)

(112)

(131)

(122)

(141)

(033)

(230)

(133)

(203)

(312)

(163)

(234)

(263)

(343)

(431)

(372)

(433)

(285)

(167)

(347)

(167)

Ca3Tb

2Si

3O

12


Ca3Tb2Si3O12,Ca3Eu2Si3O12 and Ca3Tb2Si3O12:Eu3+ (5 mol%)

Synthesized by SSR (III TT at 1450 oC x 3h)

Homogeneus white powders.Pure phase

SAMPLE DETAILS


10 20 30 40 50 60 70 80 90

Ca3Tb

2Si

3O

12

Ca3Eu

2Si

3O

12

X-r

ay

dif

fra

cti

on

inte

ns

ity

(a

rb.u

nit

s)

2 (o)

5% Eu3+

4% Eu3+

2% Eu3+

1% Eu3+

PHOTOLUMINESCENCE RESULTS

LUMINET Winter School

RT EMISSION


450 500 550 600 650 700

Ca3Eu

2Si

3O

12

No

rmalized

in

ten

sit

y (

arb

un

its)

Wavelength (nm)

Ca3Tb

2Si

3O

12

5D

4

7F

6

7F

5

7F

4

7F

3

5D

0

7F

0

7F

1

7F

2

7F

3

7F

4

450 500 550 600 650 700

Ca3Eu

2Si

3O

12

No

rma

lize

d i

nte

ns

ity

(a

rb u

nit

s)

Wavelength (nm)

Ca3Tb

1,95Eu

0,05Si

3O

12

Ca3Tb

2Si

3O

12

5D

4

7F

6

7F

5

7F

4

7F

3

5D

0

7F

0

7F

1

7F

2

7F

3

7F

4

Ca3Tb2Si3O12 and Ca3Tb2Si3O12:Eu3+: λexc =377 nm 5D3 (Tb3+)

Ca3Eu2Si3O12: λexc =393 nm 5L7 (Eu3+)

Very efficient energy transfer from Tb3+ to Eu3+

450 500 550 600 650 700

Ca3Tb

1,95Eu

0,05Si

3O

12

450 475 500 525 550

x50

No

rmalized

em

iss

ion

in

ten

sit

y

(arb

. u

nit

s)

Wavelength (nm)

5D

0

7F

0

7F

1

7F

2

7F

3

7F

4



RT EMISSION λexc =377 nm 5D3 (Tb3+)


480 510 540 570 600 630 660 690 720

480 500 520 540 560

Wavelength (nm)

Eu 1%

Eu 2%

Eu 4%

Eu 5%

x20

5D

0

Tb3+

5D

4

7F

6

7F

4

7F

3

7F

2

7F

1

Inte

nsit

y (

arb

. u

nit

s)

Wavelength (nm)

Eu 1%

Eu 2%

Eu 4%

Eu 5%

7F

0Tb3+

5D

4

7F

5

1 2 3 4 510

20

30

40

50

60

70

80

%Eu3+

7F

2(Eu

3+)/

7F

5(Tb

3+)

7F

4(Eu

3+)/

7F

5(Tb

3+)

Rati

o E

u3+/T

b3+ e

mis

sio

n a

rea

LUMINET Winter School ICR. Luminescent Materials Lab. UNIVR LUMINET Meeting. Verona 2015

RT EMISSION


1 1.2

2 1.5

4 1.8

5 1.3

Enhancement of Eu3+

luminescent.

Ca3Tb2Si3O12:Eu3+

λexc =377 nm 5D3 (Tb3+)

Ca3Eu2Si3O12:

λexc =393 nm 5L7 (Eu3+)

450 500 550 600 650 7000,0

5,0x107

1,0x108

1,5x108

2,0x108

2,5x108

3,0x108

3,5x108

4,0x108

4,5x108

Inte

nsit

y (

arb

. u

nit

s)

Wavelength (nm)

Eu1%

Eu2%

Eu4%

Eu5%

Ca3Eu

2Si

3O

12

5D

0

7F

0

7F

1

7F

2

7F

3

7F

4

Tb3+

5D

4

7F

6

Tb3+

5D

4

7F

5


RT EMISSION


450 500 550 600 650 700

Inte

ns

ity

(a

rb.u

nit

s)

Wavelength (nm)

Eu1%

Eu2%

Eu4%

Eu5%

5D

0

7F

0

7F

1

7F

2

7F

3

7F

4

λexc =393 nm 5L7 (Eu3+)

No Tb3+ emission bands are observed under direct excitation into Eu3+

These results prove no Eu3+ Tb3+ energy transfer is present No spectral shift under different excitations.


RT EXCITATION

Only a few Eu3+ excitation bands are observed (labeled with *)

These results confirm the Tb3+ Eu3+ energy transfer



325 350 375 400 425 450 475 500 525 550

7F

0

5L

8+

5G

j+

5L

9+

5L

10

7F

1

5D

4

7F

0

5D

4

7F

0

5L

6

7F

6

5G

3

7F

6

5L

8+

5G

4+

5L

7

7F

6

5G

6+

5L

9+

5G

5 7F

6

5L

10

7F

0

5D

3

7F

6

5D

3

7F

0

5L

7

7F

0

5D

2

7F

0

5D

1

7F

1

5D

1

7F

6

5D

4

No

rma

lize

d i

nte

ns

ity

(a

rb.u

nit

s)

Wavelength (nm)

Eu 1% Eu 5%

Eu 2% Ca3Tb

2Si

3O

12

Eu 4% Ca3Eu

2Si

3O

12*

**

*


RT EXCITATION



325 350 375 400 425 450 475 500 5250,0

5,0E7

1,0E8

1,5E8

2,0E8

2,5E8

3,0E8

3,5E8

4,0E8

4,5E8

Inte

nsit

y (

arb

.un

its)

Wavelength (nm)

Ca3Eu

2Si

3O

12

Ca3Tb

2Si

3O

12

Eu5%

Eu4%

Eu2%

Eu1%

Ca3Tb2Si3O12 : λemi =542 nm (Tb3+)

Ca3Eu2Si3O12and Ca3Tb2Si3O12:Eu3+ λemi =611 nm (Eu3+)

Intensity of excitation bands is enhanced, specially in near UV region


RT DECAY KINETICSOF Ca3Eu2Si3O12 AND Ca3Tb2Si3O12



0,0 0,5 1,0 1,5 2,0 2,5

exc

=377 nm emi

=545 nm d=178 s

No

rmalized

in

ten

sit

y (

arb

.un

its)

Decay time (ms)

Ca3Tb

2Si

3O

12

0,0 0,8 1,6 2,4 3,2 4,0 4,8

exc

=393 nm emi

=611 nm d=0,4ms

No

rma

lize

d i

nte

ns

ity

(a

rb.u

nit

s)

Decay time (ms)

Ca3Eu

2Si

3O

12

0,0 0,8 1,6 2,4 3,2 4,0

exc

=393 nm emi

=706 nm d=0,4ms

No

rmalized

in

ten

sit

y (

arb

.un

its)

Decay time (ms)

Ca3Eu

2Si

3O

12

Short time constant probably due to energy migration along

Ln3+ ions, because of high concentration


RT DECAY KINETICS OF Ca3Tb2Si3O12:Eu3+



0 3 6 9 12 15 18 21

0,5 1,0 1,5 2,0

Decay time (ms)

exc

=377 nm emi

=611 nm d= 1,8 ms

No

rmalized

in

ten

sit

y (

arb

. u

nit

s)

Decay time (ms)

Eu 1%

Eu 2%

Eu 4%

Eu 5%

0 3 6 9 12 15 18

exc

=377 nm emi

=706 nm d= 1,8 ms

0,5 1,0 1,5 2,0 2,5

Decay time (ms)

No

rmalized

in

ten

sit

y (

arb

. u

nit

s)

Decay time (ms)

Eu 1%

Eu 2%

Eu 4%

Eu 5%

0,00 0,08 0,16 0,24 0,32

exc

=377 nm emi

=545 nm d=11 s

No

rmalized

in

ten

sit

y (

arb

.un

its)

Decay time (ms)

Ca3Tb

2Si

3O

12:Eu3+ (5%)

Longer time constant for Eu3+

emission. Very efficient Tb3+- Eu3+

energy transfer.


CIE chromaticity coordinates



Emission colour of Ca3Tb2-xEuxSi3O12 phosphors could be tuned

effectively from green to red by adjusting Eu3+ concentration

CaTbSi Eu1% Eu2% Eu4% Eu5% CaEuSi UV excitation at 365 nm


TEMPERATURE STUDY OF Ca3Tb2Si3O12



450 480 510 540 570 600 630 660

0 60 120 180 240 3000,4

0,5

0,6

0,7

0,8

0,9

1,0

5D

4

7F

5

No

rmalized

em

issio

n

are

a (

arb

.un

its)

Temperature (K)

5D

4

7F

6

7F

5

7F

4 7F

3

Inte

nsit

y (

arb

.un

its)

Wavelength (nm)

8K

330K

Tem

pera

ture

Results confirm very fast energy migration among Tb3+ ions above 50K

λexc =370 nm into 5D3 level of Tb3+

Emission

0 50 100 150 200 250 300 350

150

200

250

300

350 Ca3Tb

2Si

3O

12

Decay t

ime (

s)

Temperature (K)

Decay kinetics (λemi =545 nm)


PHOTOLUMINESCENCE RESULTS TEMPERATURE STUDY OF Ca3Tb2Si3O12:Eu3+ (5%)


450 500 550 600 650 700 750

5D

0

7F

0

7F

1

7F

4

7F

3

460 480 500 520 540 560

Wavelength (arb.units)

Inte

ns

ity

(a

rb.u

nit

s)

Wavelength (arb.units)

x10

Tb3+

5D

4

7F

6

Tb3+

5D

3

7F

5

8K

Tem

pe

ratu

re330K

7F

2

0 60 120 180 240 300

0,2

0,4

0,6

0,8

1,0

No

rmalized

em

issio

n a

rea (

arb

.un

its)

Temperature (K)

emi

=544 nm (Tb3+

)

emi

=611 nm (Eu3+

)

emi

=703 nm (Eu3+

)

Emission



0 50 100 150 200 250 300 350

10

20

30

40

50

60

70

80

7F

2(Eu

3+)/

7F

5(Tb

3+)

Rati

o E

u3

+/T

b3

+ e

mis

sio

n a

rea

Temperature (K)

0 50 100 150 200 250 300 350

5

10

15

20

25

30

35

7F

4(Eu

3+)/

7F

5(Tb

3+)

Rati

o E

u3

+/T

b3

+ e

mis

sio

n a

rea

Temperature (K)

As temperature increases and energy migration among Tb3+ ions becomes faster, the larger is Tb3+ - Eu3+

emission ratio.



0 50 100 150 200 250 300 3500

20

40

60

80

100

120

140

160

180

200

5D

4

7F

5(Tb

3+)

Decay t

ime (s)

Temperature (K)


0 50 100 150 200 250 300 350

1,85

1,90

1,95

2,00

2,05

2,10

2,15

2,20

2,25

Decay t

ime (

ms)

Temperature (K)

5D

0

7F

2(Eu

3+)

5D

0

7F

4(Eu

3+)

Decay kinetics (λemi =611, 702 nm) Decay kinetics (λemi =544 nm)


PHOTOLUMINESCENCE RESULTS EFFICIENCY OF ENERGY TRANSFER

0 50 100 150 200 250 300 3500,4

0,5

0,6

0,7

0,8

0,9

1,0Data for undoped and 5%Eu

3+ samples

En

erg

y t

ran

sfe

r eff

icie

ncy

Temperature (K)

Efficiency of Tb3+ - Eu3+ energy transfer is more than 90% from 100 K to 350K


CONCLUSIONS

Clear evidences of energy transfer from Tb3+ to Eu3+

Tb3+ emission almost quenched and very strong Eu3+ emission

Efficient changes in the emission colour of the material by the addition of Eu3+


Energy migration among Tb3+ ions enhance Tb3+ - Eu3+ energy transfer

Tb3+ - Eu3+ energy transfer enhances Eu3+ luminescence


FUTURE WORK


Experiments at higher T to test thermal stability

Decay curves for Tb3+ emission in 1%, 2% and 4% Eu-doped samples to stimate efficiency of the

transfer

Synthesis of diluted samples in order to avoid Tb3+ concentration quenching

Thank you for your attention

LUMINESCENT MATERIALS LAB

energy transfer processes in ca tb si o :eu

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