Synthesis and Optical Properties of 2+Ba Zr Si O :Eu2 2 3 12a,b b aA. Katelnikovas , T. Jüstel , A. Kareiva

a Department of General and Inorganic Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania

b Department of Chemical Engineering, Münster University of Applied Sciences, Stegerwaldstr. 39, D-48565 Steinfurt, Germany

Introduction

Experimental Part

Ba2Zr

2Si

3O

12:8% Eu

2+

Ba2Zr

2Si

3O

12:4% Eu

2+

Ba2Zr

2Si

3O

12:2% Eu

2+

Ba2Zr

2Si

3O

12:1% Eu

2+

10 15 20 25 30 35 40 45 50 55 60

25-1466 > Ba2Zr

2Si

3O

12

Re

lati

ve

inte

ns

ity

2q

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

0

10

20

30

40

50

60

70

80

90

100

5,0 4,1 3,5 3,1 2,8 2,5 2,3 2,1 1,9 1,8 1,7 1,6

Photon energy (eV)

Re

fle

cti

on

(%)

Wavelength (nm)

0% Eu2+

0.5% Eu2+

1% Eu2+

2% Eu2+

4% Eu2+

8% Eu2+

250 300 350 400 450 500 550 600 650 700 750

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

5,0 4,1 3,5 3,1 2,8 2,5 2,3 2,1 1,9 1,8 1,7

Photon energy (eV)

Ex

cit

ati

on

inte

ns

ity

(co

un

ts)

1́0

6

Wavelength (nm)

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8 0.5% Eu

2+

1% Eu2+

2% Eu2+

4% Eu2+

8% Eu2+

Em

iss

ion

inte

ns

ity(c

ou

nts

)1́

05

282 lm/W

289 lm/W

290 lm/W

297 lm/W

304 lm/W

Eu3+

Em

iss

ion

sp

ec

tra

Ex

cit

ati

on

sp

ec

tra

350 400 450 500 550 600 650 700 750

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

Inte

ns

ity

(co

un

ts)

1́0

5

Wavelength (nm)

250 K

300 K

350 K

400 K

450 K

500 K250 300 350 400 450 500

0,0

0,2

0,4

0,6

0,8

1,0

Experimental data

Boltzmann Fit

Inte

gra

lin

ten

sit

y[n

orm

alize

dto

25

0K

]

Temperature (K)

TQ1/2

= 344 ± 6 K (» 71 °C)

0.5% Eu2+

1% Eu2+

2% Eu2+

4% Eu2+

8% Eu2+

0

5

10

15

20

25

Qu

an

tum

eff

icie

nc

y(%

)

Fig. 1. XRD patterns of samples

with various concentrations.

Ba Zr Si O2 2 3 122+Eu

Fig. 2. Reflection spectra of : .Ba Zr Si O2 2 3 12

2+Eu

Fig. 3. Excitation and emission spectra of : .Ba Zr Si O2 2 3 12

2+Eu

Fig. 4. Temperature dependent emission spectra of :2% .Ba Zr Si O2 2 3 12

2+EuFig. 5. CIE 1931 color points of

: .Ba Zr Si O2 2 3 12

2+Eu

Fig. 6. Quantum efficiencies of : .Ba Zr Si O2 2 3 12

2+Eu

Results and Discussion

Conclusions

XRD patterns of the synthesized samples are in good agreement with reference data regardless concentration (see Fig. 1). Fig. 2 shows reflection spectra of the target samples. As expected an absorption in the near UV region increases with higher concentration. The intensity of excitation and emission spectra reaches maximum (495 nm) if samples are doped with 2% (see Fig. 3). The temperature dependent emission spectra of :2% sample are depicted in Fig. 4. It turned out that emission intensity rapidly decreases with increased temperature. Calculations revealed that phosphor loses half of efficiency already at 71 C. CIE 1931 color points of synthesized phosphors are shown in Fig. 5. It is obvious that color points slightly shift towards green spectral region what is in line with emission spectra. Finally, Fig. 6 depicts quantum efficiencies of the synthesized phosphors as a function of concentration. Quantum efficiencies do not exceed 25% and is huge drawback of the phosphor for application in solid state lighting.

2+Eu

2+Eu2+ 2+Eu Ba Zr Si O Eu2 2 3 12

°

2+Eu

There are no doubts already that future lighting belongs to solid-state light sources, i.e. white LEDs. The invention of efficient blue LED enabled scientists to produce white light as a combination of blue and yellow components. But such light sources, however, possess high color temperatures and low color rendering indexes. The other possible way for producing white light is based on application of near-UV LED and several phosphors emitting in blue, green and red, therefore the demand of new phosphors emitting in those spectral regions is rapidly increasing.We demonstrate, that doped shows emission in cyan-green spectral region. The optical properties of

synthesized phosphors are discussed as a function of concentration.

2+Eu Ba Zr Si O2 2 3 12

2+Eu

All samples were prepared by 2 step solid state reaction from oxides and carbonates. First, starting materials were annealed at 3+ 2+1400°C for 5 hours under CO atmosphere in order to obtain the desired phase and partially reduce Eu to Eu . The complete

2+reduction of europium ions to Eu was obtained by annealing target samples under 5% H / 95% N gas flow for 2 hours in the 2 2

tube furnace.

In this work we demonstrated that doped phosphor possess emission in cyan-green spectral region. Quantum efficiencies do not exceed 25%, which is likely caused by photoionisation of the excited state. This explanation is in line with the strong thermal quenching of this phosphor.

2+Eu Ba Zr Si O2 2 3 12