synthesis and optical properties 3+ and ho3+ activated · 2019-09-06 · synthesis and optical...

Synthesis and Optical Propertiesof Sm3+ and Ho3+ Activated

Li3Ba2La3(MoO4)8

Florian Baur and Thomas Jüstel

11th LCS

Xuzhou, China, Nov 30th - Dec 04th, 2015

December 03rd, 2015 2Florian Baur and Thomas Jüstel

Münster University of Applied Sciences (FH Münster)

Department Chemical Engineering (~ 600 Students)

Laboratory for Material Sciences (Prof. T. Jüstel, Prof. M. Bredol, Prof. U. Kynast)

Research Group „Tailored Optical Materials“ (~ 10 Ph.D. Students + 20 undergraduates)


Tailored Optical MaterialsResearch AreasLED + FL Phosphors

Development of novel matrices and particle coatings, spectroscopic characterisation (garnets, silicates, (oxy)nitrides, carbodiimides)

Afterglow pigments

Revealing the electronic structure of Eu2+/RE3+ codoped aluminates

Governing the defect density and depth

Particle coatings of nano- or microscale luminescent pigments

Enhancement of efficiency and stability of materials by coatings due to refractive index matching and diffusion barriers

NIR Phosphors

Biocompatible luminescent materials within the optical window of biomatter, i.e. in the NIR range (diagnostics, photodynamic therapy)

VUV Phosphors

Development of optimized phosphors for noble gas excimer discharges to enable high performance UV radiation sources

Scintillators

Reduction of afterglow of materials for Computed Tomography (CT)

Ultrafast scintillator crystals for Positron Emission Tomography (PET)

Laser materials

Novel Pr3+ and Nd3+ doped fluorides as gain media

Transparent garnet ceramics


Li3Ba2Ln3(MoO4)8

• Li3Ba2Ln3(MoO4)8 is derived from Scheelite:(Ca8/8)WO4 (Li3/8Ba2/8Ln3/8)MoO4

• Various research activities regarding its potential as laser material:• Li3Ba2Y3(MoO4)8:Nd3+ - J Cryst Growth 308 (2007) 208

• Li3Ba2Y3(MoO4)8:Eu3+,Tb3+,Dy3+ - J Electrochem Soc 158 (2011) H565

• Li3Ba2Y3(MoO4)8:Er3+ - Mater Sci Eng B 176 (2011) 810

• Li3Ba2Y3(MoO4)8:Tm3+ - CrystEngComm 15 (2013) 168

• Li3Ba2Y3(MoO4)8:Yb3+ - J Alloys Compd 478 (2009) 423

• Li3Ba2La3(MoO4)8:Eu3+ - J Mater Chem 22 (2012) 22126

• Li3Ba2La3(MoO4)8:Sm3+ - Z Naturforsch B 69 (2014) 183

• Li3Ba2La3(MoO4)8:Dy3+ - J Alloy Compd 607 (2014) 110

• Li3Ba2La3(MoO4)8:Er3+ - Opt Mater 33 (2010) 36

• Li3Ba2Nd3(MoO4)8 - J Cryst Growth 381 (2013) 61

• Li3Ba2Gd3(MoO4)8:Eu3+ - J Phys Chem C 114 (2010) 3645

• Li3Ba2Gd3(MoO4)8:Er3+ - J Lumin 131 (2011) 1571

• Li3Ba2Gd3(MoO4)8:Tm3+ - Materials 7 (2014) 496

• Li3Ba2Yb3(MoO4)8 - Opt Mater 34 (2012) 1558)

• Li3Ba2Lu3(MoO4)8 - Cryst Growth Design 12 (2012) 3878

• Li3Ba2(La,Gd,Y)3(MoO4)8:Eu3+ - J Alloy Compd 479 (2009) 607

• Li3Ba2(La,Gd)3(MoO4)8:Nd3+ - J Alloy Compd 480 (2009) 839

• Li3Ba2(La-Lu,Y)3(MoO4)8 - Russ J Appl Chem 84 (2011) 384

• Li3Ba2(Gd,Tm)3(MoO4)8 - Zh Strukt Khim 33 (1992) 126

• Li3Ba2Y3(WO4)8:Yb3+ - J Lumin 132 (2012) 1507

• Li3Ba2La3(WO4)8:Dy3+ - Opt Mater 36 (2014) 1255

• Li3Ba2La3(WO4)8:Er3+,Yb3+ - PLoS ONE 7 (2012) e40631

• Li3Ba2La3(WO4)8:Tm3+ - CrystEngComm 14 (2012) 3930

• Li3BaSr(La-Lu,Y)3(MoO4)8 - Russ J Appl Chem 84 (2011) 1498

Eu3+:LBLM Ceramics and PowdersKatelnikovas, Jüstel et al. J Mater Chem 22 (2012) 22126

Sm3+:LBLM PowderBaur, Jüstel et al., Z Naturforsch B 69 (2014) 183

No reports yet on Ho3+:LBLM


Li3Ba2Ln3(MoO4)8

Ba 85%Ln 15%

Ln 67.5%Li 25%Ba 7.5%

Li MoO4

• Structure derived from Scheelite CaWO4 (Li3/8Ba2/8Ln3/8)MoO4

• Two potential Ln3+ doping sites:

[LnO10]bi-capped square prism

[LnO8]square antiprism

Russ. J. Inorg. Chem. 35 (1990) 468J. Struct. Chem. 33 (1992) 443

• monoclinic• C12/c1 (15)• 5.31 Mg/m3 (for Gd-compound)


Li3Ba2La3(MoO4)8 XRD/Synthesis

Conventional solid state synthesis

Educts: Li2CO3, BaCO3, La2O3, Sm2O3, Ho2O3, MoO3

Temperature: 800 °CDuration: 10 hours

Li3Ba2(La1-xLnx)3(MoO4)8

Li3Ba

2La

1.8Sm

1.2(MoO

4)

8

40% Sm3+

Li3Ba

2Sm

3(MoO

4)

8

100% Sm3+

Li3Ba

2La

2.4Sm

0.6(MoO

4)

8

20% Sm3+

Li3Ba

2La

0.6Sm

2.4(MoO

4)

8

80% Sm3+

Li

3Ba

2La

3(MoO

4)

8

0% Sm3+

Li3Ba

2La

1.2Sm

1.8(MoO

4)

8

60% Sm3+

10 20 30 40 50 60

Li3Ba

2Gd

3(MoO

4)

8

PDF2 (ICSD) 00-077-0830

210 20 30 40 50 60

(a)

(g)

(f)

(e)

(d)

(c)

(b)

Li3Ba

2Gd

3(MoO

4)

8

PDF2 (ICSD) 00-077-0830

2

(a)

A complete solid solution series existswith good crystallinity and phaseformation for all lanthanoid ratios


Li3Ba2La3(MoO4)8 SEM

• Sharp, regular formed primary particles: ~5 µm diameter + some „dust“

• Agglomerates: ~20-30 µm diameter

• The particle morphology and lowmelting point of molybdates arefavorable for laser ceramics preparation


Sm3+:Li3Ba2La3(MoO4)8 Reflection

300 400 500 600 700 800

0

20

40

60

80

100

11

10

8

79

6

5

3

2

4

Li3Ba

2La

3(MoO

4)

8

Li3Ba

2Sm

3(MoO

4)

8

Re

fle

cta

nc

e (

%)

Wavelength (nm)

Ho

st

latt

ice

1

4.5 4 3.5 3 2.5 2

Nr. Transition 6H

5/2

1 6H

5/2

4D

7/2+

4D

9/2

2 6H

5/2

4D

3/2+

4P

3/2

3 6H

5/2

4D

1/2+

4L

17/2+

6P

7/2

4 6H

5/2

4H

11/2+

6M

15/2+

4M

21/2

5 6H

5/2

4L

13/2+

6P

3/2+

4F

7/2

6 6H

5/2

4M

19/2+

6P

5/2

7 6H

5/2

4I15/2

+4G

9/2+

4M

17/2

8 6H

5/2

4I13/2

+4I11/2

+4I9/2

+4M

15/2

9 6H

5/2

4G

7/2

10 6H

5/2

4F

3/2

11 6H

5/2

4G

5/2

Photon energy (eV)

• Optical band gap: ~320 nm; 3.65 eV

• Broadening of the absorption band in the doped samples likely stems from O2-/Sm3+ charge transfer

• The 4f-4f transitions of Sm3+ exhibit unusually strong absorption in LBLM

• Reflectance is close to 100% in the orange to red spectral region which is important for high efficiency

• Pumping is possible via one of themultiplets between 360 and 550 nm


Sm3+:Li3Ba2La3(MoO4)8 Emission & Excitation

• CT band consists of two components(282 nm/4.40 eV & 310 nm/4.01 eV): Sm3+ and Mo6+ CT bands

• Branching ratio 4G5/26H9/2: 59%

250 300 350 400 450 500 550 600

11109

8

7

6

5

4

32

Inte

nsit

y (

a.u

.)

Wavelength (nm)

CT

em = 645 nm

1

600 650 700 750 800

4G

5/2

6H

11

/2

4G

5/2

6H

9/2

4G

5/2

6H

7/2

4G

5/2

6H

5/2

ex = 404.5 nm

Li3Ba

2La

3-xSm

x(MoO

4)

8

(b)

Inte

nsity

(a.u

)

x = 0.015 (0.5%)

x = 0.15 (5%)

Wavelength (nm)

ex = 404.5 nm

(a)

500 550 600 650 700 750 800

0.1%

0.5%

1%

2%

5%

10%

20%

100%

Inte

gra

l in

ten

sit

y (

a.u

.)

Comment (Type)

4,5 4 3,5 3 2,5

Photon energy (eV)2,2 2,1 2 1,9 1,8 1,7 1,6

Photon energy (eV)

• Highest emission intensities can be foundfor the 5% Sm3+ sample!

• Shape and relative emission intensitiesdo not change with Sm3+ concentration


Sm3+:Li3Ba2La3(MoO4)8 Emission f(T)

• With decreasing temperature lines sharpen due to lowered vibronic interactions

• A small blue-shift can be observed, presumably caused by lattice constriction (cf. red-shift caused by high-pressure: Rad Eff Defect Solid 169 (2014) 48))

• A bi-sigmoidal behaviour was observed, likely resulting from competitive absorption of host material and Sm3+

• T1/2,a = 280 K (EA = 0.2 eV)• T1/2,b = 515 K (EA = 0.6 eV)

550 600 650 700 750

Wavelength (nm)

100 K

500 K

Inte

ns

ity

(a

.u.)

100 200 300 400 500

0,0

0,2

0,4

0,6

0,8

1,0

Temperature (K)

Experimental data

Double Fermi-Dirac Fit

ex

= 404 nm

No

rma

lize

d e

mis

sio

n i

nte

gra

l (a

.u.)

2,2 2,1 2 1,9 1,8 1,7

Photon energy (eV)

-200 -100 0 100 200

Temperature (°C)


Sm3+:Li3Ba2La3(MoO4)8 Decay

• Decay behaviour strongly depends on Sm3+ concentration

• Fast non-radiative processes (cross-relaxation 4G5/2

6F5/2 / 6H5/26F11/2)

shorten the decay time at higher Sm3+

concentrations

• Bi-exponential decay curve atconcentrations larger than 2% isassumedly linked to second doping site

• IQE = Wr/(Wr+Wnr) – begins to decrease at concentration larger than 0.25%


Sm3+:Li3Ba2La3(MoO4)8 Decay f(T)

• Decay times remain constant up to 500 K

• IQE remains constant up to 500 K,contrary to emission intensity photon escape effeciency decreases

• This observation might be explained by temperature-driven reversible formation of Mo5+ defects

• Lower decay time at 100 K might be an outlier or start of a trend

• He-cryostat measurements necessary for further investigation

0 1 2 3 4 5

101

102

103

Time (ms)

T = 100 K

T = 500 K

Co

un

ts

100 200 300 400 500

680

700

720

740

Temperature (K)

1/2

Tim

e (n

s)

300 400 500 600 700 800

Temperature (°C)


Sm3+:Li3Ba2La3(MoO4)8 Quantum Efficiencies

• A relatively high QE of 44% could be realized, this is rare in crystalline materials where high phonon frequencies quench Sm3+

NIR transitions

• Decay constants (i.e. IQE) decrease with increasing Sm3+

concentration, probably caused by cross-relaxation processes


Ho3+:Li3Ba2La3(MoO4)8 Reflection

• The 4f-4f transitions of Ho3+ exhibit unusually strong absorption in LBLM

• 1% Ho3+ exhibits only 60% reflection around 450 nm, which is useful for pumping with blue laser diodes

• Reflectance approaches 100%, indicating high sample quality

• Host absorption band is broader than in the undoped material

250 300 350 400 450 500 550 600 650 700 750 800

0

20

40

60

80

100

0

20

40

60

80

100

5I8

5F

5

5I8

5G

6

Re

flec

tan

ce

/%

Re

fle

cta

nc

e /

%

Wavelength /nm

5I8

5G

5

4.5 4 3.5 3 2.5 2Energy /eV

Ho

st

ab

so

rpti

on

5I8

5F

4 +

5S

2


Ho3+:Li3Ba2La3(MoO4)8 Emission & Excitation

• Most efficient excitation via 5I8

5G6 peaking at 452 nm

• Excitation via CT bands results in very low QE, which is commonly observed in molybdates

• Highest emission intensity was observed for the 1% doped sample

250 300 350 400 450 500 550 600 650 700 750 800

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

No

rmaliz

ed

Inte

nsity

/co

un

ts

ex

= 453 nm

em

= 545 nm

No

rmalized

In

ten

sit

y /co

un

ts

Wavelength /nm

4.5 4 3.5 3 2.5 2Energy /eV

• Decay times are unusually fast, measurement with µs-flashlamp was not possible

• This is likely a result of concentration quenching and samples with even lower activator concentration will be prepared


Ho3+:Li3Ba2La3(MoO4)8 Emission f(T)

• Broadening of the lines with increasing temperature is less pronounced than usually observed

535 540 545 550

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0 100 K

125 K

150 K

175 K

200 K

225 K

250 K

275 K

300 K

325 K

350 K

375 K

400 K

425 K

450 K

475 K

500 KN

orm

aliz

ed

Inte

nsity

/co

un

ts

No

rmalized

In

ten

sit

y /co

un

ts

Wavelength /nm

4.5 4 3.5 3 2.5 2Energy /eV

• Relative intensities of the high energy lines of the multiplet increases

• This might be related to the emission originating from two separate levels: 5F4 & 5S2

• The position of the lines does not shift with temperature


Ho3+:Li3Ba2La3(MoO4)8 Emission f(T)

• Bi-sigmoidal behaviour similar to that of the Sm3+ doped sample

• This seems to be a characteristic property of LBLM host material and molybdates in general, see F. Baur & T. Jüstel, Aust J Chem 68 (2015) 1727

100 150 200 250 300 350 400 450 500

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Emission integral LBLM:Ho3+

(1%)

Double Fermi-Dirac Fit

Em

issio

n In

teg

ral

Temperature /K

T1/2,1

= 261 K

T1/2,2

= 454 K

ex

= 452 nm

• T1/2,a = 260 K(assigned to CT excitation)

• T1/2,b = 455 K(assigned to Ho3+ 4f-4fexcitation)


Er3+:Li3Ba2La3(MoO4)8 Emission & Excitation

• Potential upconversion in Ho3+/Er3+ co-doped LBLM will be investigated

• First experiments with LBLM:Er3+ powder samples

• Single-phase material was synthesized

• Strong absorption of 4f-4ftransitions was observed

300 400 500 600 700 800

0.00

0.25

0.50

0.75

1.00

Excitation (em

=551.5 nm)

Emission (ex

=376.5 nm)

Reflectance

Inte

nsit

y (

no

rmalized

) [a

.u.]

Wavelength [nm]

Li3Ba

2La

3(MoO

4)

8:Er

3+ (2 %)

0

25

50

75

100

Refle

cta

nce [%

]


Li3Ba2La3(MoO4)8 Conclusions

• High-quality, single-phase powder samples of Li3Ba2La3(MoO4)8 doped with Sm3+, Ho3+

or Er3+ were synthesized employing conventional solid state synthesis

• SEM images revealed particles (diameter ~ 5 µm) with a relatively uniform morphology, suitable for sintering towards transparent ceramics

• Strong absorption from the forbidden 4f-4f transition could be observed even in low-doped samples

• 44% EQE was found in the LBLM:Sm3+ (2%) sample

• Temperature-dependence of IQE and EQE differ, indicating a decrease in photon escapeefficiency at elevated temperatures

• LBLM:Ho3+ exhibits very fast decay (low figure µs-range), very low dopantconcentrations will be required to increase decay times

• LBLM:Er3+ powder samples were successfully prepared and first measurements of theoptical properties conducted


THANK YOU FOR YOUR ATTENTION

synthesis and optical properties 3+ and ho3+ activated · 2019-09-06 · synthesis and optical...

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