Temperature Dependent Decay Measurements of Doped 2+ Garnets and Eu Doped Sulfides and Sulfoselenides MAF 11
3+ Ce
Helga Bettentrupa, Holger Winklerb , Dominik Uhlicha, Thomas Jüstela aUniversity
of Applied Sciences Münster, Stegerwaldstr. 39, D-48565 Steinfurt (Germany). e-mail:
[email protected] bMerck KGaA, Frankfurter Straße 250, D-64293 Darmstadt (Germany)
Introduction Eu2+ and Ce3+ activated phosphors are widely applied in phosphor converted light emitting diodes (pcLEDs). These are the most favoured activator ions because of their tuneable emission colour, fast decay, and their broad excitation range. Another advantage is their high quantum efficiency also at elevated temperatures; however, this strongly depends on the host lattice. In this study, Ce3+ activated garnets and Eu2+ activated sulfides and sulfoselenides were investigated with respect to their thermal quenching and to their fluorescence lifetime between 100 and 500 K.
Due to the fact that high power LED dies have a working temperature of 373 K or even higher, temperature dependent characterisation of LED phosphors are necessary. The measurements were performed on an Edinburgh Instrument FLS920 fluorescence spectrometer equipped with a 450 W xenon discharge lamp for steady state and an EPL 440 LASER diode for lifetime measurements, a Microstate N from Oxford Instruments for working with liquid N2 and a R2658 photomultiplier tube from Hamamatsu cooled to -20 °C for detection was used.
Temperature Dependent Emission Spectra and Quenching Curves
4
2,0x10
600
650
700
750
0,94106 Standard Error
0,6
1
Normalized Integral A2
0
0
Normalized Integral x0
713,45428
34,84361
Normalized Integral dx
100,73301
13,81355
0,4
0,2
(BaxSr1-x)Ga2(SySe1-y)4:Eu2+ λEx= 450 nm slit size: Ex = 4.00 nm, Ex = 0.70 nm 100.0 K 200.0 K 300.0 K 400.0 K 500.0 K
Intensity [counts]
1,25x105
5
1,00x10
4
7,50x10
4
5,00x10
2,50x104
0,00 450
500
550
150
200
600
650
1,0
λEx= 450 nm slit size: Ex = 4.00 nm, Ex = 0.70 nm 100.0 K 200.0 K 300.0 K 400.0 K 500.0 K
Intensity [counts]
1,25x10
1,00x105
7,50x104
5,00x104
4
2,50x10
0,00 450
500
550
600
650
y = A2 + (A1-A2)/(1 + exp((x-x0)/dx))
700
750
A1
1
0
Normalized Integral
A2
0
0
Normalized Integral
x0
437,09725
1,35768
Normalized Integral
dx
29,315
1,22444
Emission Integral λEx= 450 nm Boltzmann Fit 150
200
Boltzmann y = A2 + (A1-A2)/(1 + exp((x-x0)/dx))
Reduced Chi-Sqr
300
350
400
450
500
0
1000
2000
Standard Error
Normalized Integral A1
1
0
Normalized Integral A2
0
0
Normalized Integral x0
844,54967
154,9456
Normalized Integral dx
134,96929
52,25968
0,4
0,2
750
800
3000
400
450
500
Temperature [K] 500
(BaxSr1-x)Ga2(SySe1-y)4:Eu2+
400
4000
Model
Boltzmann
Equation
y = A2 + (A1-A2) /(1 + exp((x-x0)/ dx))
Reduced Chi-Sq r
300
100,46475
Adj. R-Square
0,9959 Value
Standard Error
average time
A1
448,36679
average time
A2
0
6,30753 0
average time
x0
446,44104
1,77509
average time
dx
26,91353
1,61781
200
average decay time τav λEx= 445.60 nm, λEm= 536.00 nm Boltzmann fit
100
250
5000
300
350
400
450
500
Temperature [K]
Y3Al5O12:Ce3+
λEx= 445.6 nm, λEm= 560 nm Em slit = 3.00 nm T=275.00 K T=500.00 K
60 50
100
40 30 20
10
Emission Integral λEx= 450 nm Boltzmann Fit
0,0 100
150
200
1
250
300
350
400
450
500
0
200
400
Boltzmann
Equation
y = A2 + (A1-A2)/(1 + exp((x-x0)/d x))
Adj. R-Square
6,08175E-4 0,99604 Value
Standard Error
Normalized Integral A1
0,4
0,2
0,0 100
1
0
Normalized Integral A2
0
0
Normalized Integral x0
355,21237
2,85914
Normalized Integral dx
44,7516
2,54058
Emission Integral λEx= 450 nm Boltzmann Fit 150
200
800
0 250
1000
250
800
λEx= 445.60 nm, λEm= 605.00 nm Em slit: 5.00 nm 100.0 K 200.0 K 250.0 K 275.0 K 300.0 K 325.0 K 350.0 K 400.0 K
1000
350
400
450
500
0
1000
Temperature [K]
The slight decrease in luminescence intensity of the Ce3+ doped garnets Lu3Al5O12 and Y3Al5O12 with increasing temperature is due to re-absorption caused by the broadening of the excitation and emission band. The decay measurements proved that quenching of the excited state of the activator is not an issue up to 500 K. The colour point of both garnets are almost stable in the 100 – 500 K range.
350
2000
3000
400
450
500
4000
CaSxSe1-x:Eu2+
700
Model
Boltzmann
Equation
y = A2 + (A1-A2)/(1 + exp((x-x 0)/dx))
Reduced Chi-Sqr
125,91747
Adj. R-Square
100
300
300
Temperature [K]
CaSxSe1-x:Eu2+
Model
Reduced Chi-Sqr
600
Time [ns]
CaSxSe1-x:Eu2+
0,6
decay time τ1 λEx= 445.6 nm, λEm= 560 nm
10
0,8
700
350
1000
0,40792 Value
0,6
300
Time [ns]
3,42529E-4
Adj. R-Square
0 250
1000
100
Y3Al5O12:Ce3+
Equation
800
10
250
Model
600
λEx= 445.60 nm, λEm= 536.00 nm Em slit: 5.00 nm 250.0 K 350.0 K 425.0 K 450.0 K 475.0 K 500.0 K
1000
Y3Al5O12:Ce3+
0,8
Normalised Intensity [a.u.]
Intensity [counts]
Conclusions
400
10000
1x10
Wavelength [nm]
Standard Error
Normalized Integral
0,4
0,2
Decay time τ1 λEx= 445.6 nm, λEm= 520 nm
Time [ms]
0,99805 Value
0,6
1,0
5
650
200
Temperature [K]
2x105
600
0
10000
800
λEx= 450 nm slit size: Ex = 4.00 nm, Ex = 0.70 nm 4x105 100.0 K 200.0 K 300.0 K 400.0 K 3x105 500.0 K
550
1
500
2,08604E-4
Adj. R-Square
1,0
CaSxSe1-x:Eu2+
500
450
10000
Boltzmann
Wavelength [nm]
0 450
400
Temperature [K]
Y3Al5O12:Ce3+
5
350
(BaxSr1-x)Ga2(SySe1-y)4:Eu2+
Model
0,0 100
700
Normalised Intensity [a.u.]
1,50x10
300
Equation
Reduced Chi-Sqr
20
10
(BaxSr1-x)Ga2(SySe1-y)4:Eu2+
0,8
30
10
250
Wavelength [nm]
5
100
Temperature [K]
Normalised Intensity [a.u.]
1,50x10
40
Emission Integral λEx= 450 nm Boltzmann Fit
Wavelength [nm] 5
0
Decay Time [ns]
Value Normalized Integral A1
0,0 100
800
1000
50
Decay Time [ns]
550
8,13943E-5
λEx= 445.6 nm, λEm= 520 nm Em slit = 3.00 nm T=250.00 K T=500.00 K
Average Decay Time [ns]
4,0x104
Reduced Chi-Sqr Adj. R-Square
Lu3Al5O12:Ce3+
Average Decay Time [ns]
6,0x10
500
y = A2 + (A1-A2)/(1 + exp((x-x0)/dx))
Lu3Al5O12:Ce3+
600
Value
500
Standard Error
A1
733,20101
average time
A2
0
0
average time
x0
266,93217
7,31813 1,09235
average time
dx
22,1817
0,90461
400 300 200
average decay time τav 100 λEx= 445.60 nm, λEm= 605.00 nm Boltzmann Fit 0 100
5000
0,99868
average time
150
200
250
300
350
400
Temperature [K]
Time [ns]
1,0
doped sulfoselenide The luminescence of the and sulfide is nearly completely quenched at 500 K, which is in line with our decay measurements. The distinct blue shift of the emission band of both Eu2+ phosphors is assigned to the decrease in crystal field splitting of the d-levels of the excited [Xe]4f65d1 configuration caused by thermal expansion of the host lattice.
Colour Points (C.I.E. 1931) (BaxSr1-x)Ga2(SySe1-y)4:Eu2+
Eu2+
520
0,8
Lu3Al5O12:Ce3+ Y3Al5O12:Ce3+
530 540
510
0,6 500
K CaSxSe1-x:Eu2+ 105500 K60 5010005 K0 K K 50 155070000 K 580
y
4
0,0 450
Equation
Intensity [counts]
8,0x10
Boltzmann
10000
Intensity [counts]
4
Model
0,8
Normalised Intensity [a.u.]
1,0x105
Intensity [counts]
1,0
λEx= 450 nm slit size: Ex = 4.00, Em = 0.50 100.0 K 200.0 K 300.0 K 400.0 K 500.0 K
Intensity [counts]
1,2x10
Lu3Al5O12:Ce3+
Intensity [counts]
Lu3Al5O12:Ce3+
5
Temperature Dependent Decay Measurements
K 500
590
0,4
600
490
K 100
610 0 62 30 6 700
0,2 480
0,0 0,0
470 464050 0 38
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
x
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