Luminescence of co-doped Sr5MgLa2(BO3)6:Ce3+,Mn2+ Matthias Müller, Stefan Fischer, and Thomas Jüstel Münster University of Applied Sciences, Stegerwaldstraße 39, D-48565 Steinfurt, Germany Conclusions
Experimental Section
• Diffuse reflectance measurement prove the white body colour and high powder quality of the synthesized samples.
• Sr5Mg1-xMnx(La0.99Ce0.01)2(BO3)6 samples were synthesized by using a high temperature solid state reaction.
• Co-doped Sr5Mg1-xMnx(La0.99Ce0.01)2(BO3)6 exhibits two emission bands under UV excitation, located at 397 and 714 nm. occupies two distinct • Ce3+ Sr5Mg1-xMnx(La0.99Ce0.01)2(BO3)6.
crystallographic
sites
in
• The samples were primarily annealed at 650 °C for 1 h in air and finally sintered in alumina-crucibles at 1200 °C for 6 h in reducing CO atmosphere.
co-doped
• Phase purity was investigated using X-ray powder diffractometry.
• The highest photoluminescence intensity was found for a Mn2+ concentration of x = 0.10. At higher concentrations a saturation effect sets in.
• Optical properties were investigated by recording photoluminescence spectra as well as by performing PL lifetime measurements at different temperatures.
• T1/2 of co-doped Sr5Mg0.90Mn0.10(La0.99Ce0.01)2(BO3)6 was found to be 355 K.
Results
0
Fluorescence lifetime /ns
300
350
400
450 500 550 600 Wavelength /nm
650
700
750
800
Reflectance (%)
Diffuse reflectance spectra of selected samples.
PLE (em = 715 nm) PLE (em = 400 nm) PL (ex = 300 nm)
C
Relative intensity (a.u.)
0.8
Emission and excitation spectra of selected samples.
Normalized intensity (a.u.)
1.0
200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 Wavelength /nm
100
200
300 400 Temperature /K
500
ex = 300 nm
10
Sr5Mg(La0.99Ce0.01)2(BO3)6 Reflectance standard: BaSO4
Sr5Mg0.90Mn0.10(La0.99Ce0.01)2(BO3)6
c
0.0
0.4
Sr5Mg0.97Mn0.03La2(BO3)6
0.0 250
0.2
T
10
Ce1
0.6
B
1.0 0.8
-1
10
0.00
250
300 350 Wavelength /nm
500
ex = 265 nm
10
0.0 200
300 400 Temperature /K
em = 400 nm
-2
-3
0.2
200
10
0.4
0
T = 100 K T = 400 K T = 500 K
50
100
0
100
200
150 Time /ns
200
250
300
300
400
500
Time /ns
Energy transfer efficiency of Sr5Mg1-xMnx(La0.99Ce0.01)2(BO3)6 increases with increasing Mn2+ concentration. 0
100
0.20
x = 0.00 x = 0.10 x = 0.20
-2
10
15
0.05 0.10 0.15 Mn concentration x
10
25
10
0.6
0.00
-3
30
20
0.10 0.05
-1
10
Logarithmic intensity (arb. unit)
Sr5MgLa2(BO3)6
0.2
PL (ex = 415 nm)
Logarithmic intensity (arb. unit)
Relative intensity (arb. unit)
0.4
PLE (em = 715 nm)
0.4
Photoluminescence of Sr5Mg0.90Mn0.10(La0.99Ce0.01)2(BO3)6 shows good temperature stability (T1/2 = 355 K).
0.6
Sr5Mg0.97Mn0.03La2(BO3)6
b
0.15
0.6
0.0 320350 400 450 500 550 600 650 700 750 800 850 900 Wavelength /nm
0.8
PLE (em = 400 nm) PL (ex = 300 nm)
10
0.8
0.2
1.0
Sr5Mg(La0.99Ce0.01)2(BO3)6
0.6
0.20
0
1.0
Fluorescence lifetime /ms
Relative intensity (arb. unit)
0.8
• The colour point of the emission of Sr5Mg1-xMnx(La0.99Ce0.01)2(BO3)6 can be varied in the blue colour range by increasing the Mn2+ concentration.
a
100 K 150 K 200 K 250 K 300 K 350 K 400 K 450 K 500 K
Logarithmic intensity (arb. unit)
1.0
• Energy transfer efficiency ηT of co-doped Sr5Mg1-xMnx(La0.99Ce0.01)2(BO3)6 increases with increasing Mn2+ concentration.
Rel. PL integral (arb. unit)
• Furthermore, diffuse reflectance measurements were executed (reflectance standard: BaSO4).
• Temperature dependent luminescence lifetime measurements revealed that thermal quenching in Sr5Mg0.90Mn0.10(La0.99Ce0.01)2(BO3)6 is mainly caused by the Mn2+ ions.
50 40 30 20 10 0 100
10
200
300 400 Temperature /K
500
-1
ex = 265 nm em = 400 nm
10
-2
0
T = 100 K T = 400 K T = 500 K
5
10
15
20 Time /ms
25
30
35
40
Inset: PLE (em = 345 nm) PLE (em = 380 nm)
0.4
PLE (em = 415 nm)
T = 2.9 K
Ce2
0.2
PL decay curves of Sr5Mg0.90Mn0.10(La0.99Ce0.01)2(BO3)6 reveal good temperature stability Ce3+ emission.
Thermal quenching in Sr5Mg0.90Mn0.10(La0.99Ce0.01)2(BO3)6 is mainly caused by the Mn2+ ions.
D A
Sr5Mg(La0.99Ce0.01)2(BO3)6 PL (ex = 300 nm, T = 2.9 K)
x = 0.000 x = 0.005 x = 0.010 x = 0.015 x = 0.020 x = 0.050 x = 0.100 x = 0.150 x = 0.200
520 530
0.8
540
510
0.0 320 350
550 560
0.6
400
450
500 550 600 Wavelength /nm
650
700
750
800
Ce3+ occupies two distinct crystallographic sites. 1.0
580
ex = 300 nm 600
0.8
610 490
680
0.2 480 470
0.0
420
0.0
0.2
0.4
0.6
0.8
Relative intensity (arb. unit)
y
590
0.4
0.6
0.8
0.2
400
450
0.4
• Unfortunately, these light sources are unpopular for domestic lighting due to high colour temperature and low colour rendering index (CRI)
0.2 0.0 0.05
0.10 0.15 concentration x
0.20
500 550 600 Wavelength /nm
650
• One approach to obtain reasonable CRIs, is to use a phosphor blend comprising a blue, green, and red phosphor, which is excited by an ultraviolet emitting LED.
700
750
800
Highest photoluminescence intensity of Mn2+ was found for x = 0.10.
Acknow ledgement The authors are grateful to Merck KGaA Darmstadt, Germany for generous financial support.
Matthias Müller Department of Chemical Engineering Inorganic Chemistry and Material Science Research Group Prof. Dr. Thomas Jüstel Phone +49 2551 9-62851 e-mail:
[email protected],
[email protected]
• Nowadays, most of the commercially available white light emitting pcLEDs comprise a blue emitting (In,Ga)N chip pumping a green-yellow emitting phosphor, e.g. (Y,Gd)3Al5O12:Ce3+.
Mn Ce
0.6
x = 0.000 x = 0.005 x = 0.010 x = 0.020 x = 0.050 x = 0.080 x = 0.100 x = 0.150 x = 0.200
0.4
0.0 320 350
1.0
0.00
x
Colour points of co-doped Sr5Mg1-xMnx(La0.99Ce0.01)2(BO3)6 with different Mn2+ contents.
Relative intensity (arb. unit)
570 500
Background
• However, these packages underlie a loss in blue emission due to re-absorption by the green and red phosphors. • Alternatively, the ion couple Ce3+ and Mn2+ can be used. The broad emission bands in the blue and red spectral range of Ce3+ and Mn2+ in many host materials complement each other to white light due to additive colour mixing. • Ce3+ usually exhibits a broad excitation band in the UV range and is well appropriated for pumping by UV LEDs. Additionally, the blue emission band of Ce3+ is also suitable to sensitize the spin and parity forbidden [Ar]3d5-[Ar]3d5 transitions of Mn2+ via energy transfer.
