Poster for international scientific conference "Open Readings 2011"

1. LUMINESCENCE OF NOVEL CERIUM – DOPED PHOSPHORS
FOR WHITE LEDS
K. Nalivaika, G. Tamulaitis
Semiconductor Physics Department and Institute of Applied Research, Vilnius University,
Saulėtekio ave. 9 – III, LT – 10222 Vilnius, Lithuania
Kristijonas.Nalivaika@ff.stud.vu.lt
Introduction
Solid-state lighting technology is improving rapidly and emerges as energy-efficient alternative to conventional lighting sources. Currently, much effort is being put into
improving efficiency and color rendering of the solid-state lamps designed for general lighting. The most popular phosphor in phosphor conversion light emitting diodes
(LEDs) is YAG:Ce. It offers best efficiency and strong absorption in blue spectral region but suffers from the insufficient red component in the emission band. One of the most
important issues in phosphor conversion LEDs is search for new phosphors ensuring good efficiency as well as better color rendering than the currently most popular YAG:Ce.
Object under investigation Results Ce content 0,25%
In this work a set of Y3-xLuxAl3MgSiO12:Ce3+
phosphors consisting of 16 samples with different relative Spectra of Y3-xLuxAl3MgSiO12:Ce3+ phosphors 1,0 Composition
3+
Y3Al3MgSiO12:Ce
numbers of Y and Lu atoms and different cerium content redshift when the relative number of Lu atoms is 3+
Photoluminescence
Y2LuAl3MgSiO12:Ce
intensity (s.v.)
0,8
(0.25%, 0.5%, 0.5% and 1%) was under study. All samples decreased in favour of Y atoms. This is caused by YLu2Al3MgSiO12:Ce
3+
were annealed at 1600°C. the crystal field alteration due to change in ion 0,6
Lu3Al3MgSiO12:Ce
3+
diameter [1]. Spectra of Y3-xLuxAl3MgSiO12:Ce3+
Composition of the samples under study is presented in phosphors are red-shifted from 3 to 15 nm 0,4
the first two columns of the table below, while Ce content compared with the most widely used YAG:Ce
is are listed in the third column. phosphor. This shift is very beneficial for better 0,2
color rendering of white LEDs.
0,0
Y3 0,25% Ce3+ 500 550 600 650 700 750 800
 (nm)
Y2Lu 0,5% Ce3+ 4500
Al3MgSiO12
YLu2 0,75% Ce3+ Phosphors with 0,5% of cerium exhibited the Lu3Al3MgSiO12:Ce3+
highest luminescence intensity, regardless of the 4000
Photoliuminescence
YLu2Al3MgSiO12:Ce3+
Lu3 1% Ce3+ composition of crystal matrix. A decrease in
intensity (a.u.)
luminescence intensity at increasing Ce 3500
The powdered phosphors were contained in special concentration from 0.5% to 1% due to Y2LuAl3MgSiO12:Ce3+
plexiglas cells. concentration quenching effect [2] was also 3000
observed.
2500 Y3Al3MgSiO12:Ce3+
0,25 0,50 0,75 1,00
90
Ce content (%) Cerium content (%)
85 0,25
Experimental setup 80
0,5
0,75
1,0
QY value depends on the matrix composition.
The more Lu and less Y atoms there are in the
QY (%)
75
Measurements were carried out using an integrating sphere compound, the higher QY is exhibited. The
and spectrophotometer. A blue InGaN LED was used for 70
highest of all QY value was observed in
excitation. The setup used for measuring the quantum yield 65
Lu3Al3MgSiO12:Ce3+ phosphor with the 0,25%
(QY) is shown below. 60
of Ce, while lowest – in Y3Al3MgSiO12:Ce3+
55 phosphor with 1% of Ce.
50
45
Y3-xLuxAl3MgSiO12:Ce3+
90
0 1 2 3 Lu3Al3MgSiO12:Ce3+
Composition (x) 85
80
75
QY decreased with an increase of Ce
QY (%)
70
concentration. When cerium content is increased
from 0,25% to 1% QY of Lu3Al3MgSiO12:Ce3+ 65
phosphor decreases from 89% to 66%. 60
Measurements were carried out using three configurations: 55 Y3Al3MgSiO12:Ce3+
(A) without a sample in a sphere, (B) with a sampe inside not 50
being directly excited, and (C) with a sample inside being 45
directly excited. 0,25 0,50 0,75 1,00
Cerium content (%)
Reference
[1] A. Katelnikovas, T. Bareika, P. Vitta, T. Justel, H. Winkler,
Conclusions
A. Kareiva, A. Žukauskas, G. Tamulaitis, Y3-xMg2AlSi2O12:Cex The luminescence band of Y3-xLuxAl3MgSiO12:Ce3+ phosphors redshifts with an increase of Ce
phosphors – prospective for warm-white light emitting diodes, Optical concentration and Y/Lu ratio. Maximal shift in respect of YAG:Ce luminescence band is 42 nm. This
Materials, 32, 1261 (2010). enables obtaining warmer white light when the phosphor is used with blue LED.
[2] Haranath, Chander, Sharma, Singh, Enhanced luminescence of High values of QY (up to 89% in Lu3Al3MgSiO12:0,25% Ce3+ sample) were observed in these sol – gel
Y3Al5O12:Ce3+ nanophosphor for white light emitting diodes, Appl.
derived phosphors. However the QY decreased rapidly with the increase of cerium content (down
Phys. Lett., 89, 173118 (2006).
to 68% in the sample with 1% Ce).