PROPERTIES OF Eu3+ LUMINESCENCE IN ... - Ceramics-Silikaty

Relative intensity (a.u.)
Figure 3. Emission intensity vs europium concentration (x) of
Ba 2-xMgSi 2O 7: Eu x 3+ phosphor under various excitation wavelengths
(λ em = 614 nm).
The emission intensity (I) per activator ion follows
the equation [22, 23]:
where x is the activator concentration; Q = 6, 8, 10 for
dipole-dipole(d-d), dipole-quadrupole(d-q), quadrupolequadrupole(q-q)
interactions, respectively; and K and
β are constant for the same excitation conditions for a
given host crystal. The critical concentration of Eu 3+
has been determined to be 0.05 mol. The dependence
of the emission intensity of Ba 2MgSi 2O 7: Eu 3+ phosphor
excited at 394 nm as a function of the corresponding
concentration of Eu 3+ for concentration greater than
the critical concentration is determined. The polt of
lg I/x Eu 3+ as a function of lg x Eu 3+ in Ba 2-xMgSi 2O 7: Eu x 3+
phosphor are shown in Figure 4. It can be seen that
dependence of lg x Eu 3+ on lg I/x Eu 3+ is linear and the slope
is -1.989. The value of Q can be calculated as 5.967,
which is close to 6. The result indicates that the con-
centration self-quenching mechanism of Eu 3+ luminescence
in Ba 2MgSi 2O 7 is the d-d interaction.
3+
lg I/x Eu
λ ex = 394 nm
λ ex = 465 nm
λ ex = 381 nm
λ ex = 362 nm
λ ex = 413 nm
0 0.02 0.04 0.06 0.08 0.1
Eu concentration (x)
6.0
5.5
5.0
4.5
4.0
3.5
-2.0 -1.8 -1.6
3+ lg xEu -1.4 -1.2
Figure 4. Plot of lg I/x 3+
Eu as a function of 1 lg x 3+
Eu in Ba2 3+
xMgSi2O7: Eux phosphors (λex = 394 nm).
Yao S., Xue L., Yan Y.
-1.0
The excitation spectra of Ba 1.95MgSi 2O 7: Eu 0.05 3+
is measured in the wavelength range of 260-465 nm by
monitoring with the intense red emission located at 614
nm (Figure 5a). The excitation spectra consist of two
intense bands at 394 and 465 nm in addition to three
relatively weak bands peaking about 362, 381, and 413
nm. The bands peaking around 362, 394 and 465 nm are
assigned to transition from the 7 F 0 level to the 5 D 4, 5 L 6,
and 5 D 2 levels of f-f transitions of Eu 3+ , respectively. On
the other hand, rest of the bands peaking around 381 and
413 nm are assigned to the transitions from the thermal
populated 7 F 1 level to the 5 F 4 and 5 L 3 [24, 25]. The strong
broad band peaking at 394 nm and the narrow band at
465 nm correspond to the characteristic f-f transitions
of Eu 3+ within its 4 f 6 configuration. Figure 5b shows
the emission spectral of as-synthesized Eu 3+ -doped
Ba 2MgSi 2O 7 phosphors. The spectrum exhibits two main
peaks centered at 591 and 614 nm, which come from the
transitions of 5 D 0→ 7 F 1 and 5 D 0→ 7 F 2, respectively. The
most intense emission is the 5 D 0→ 7 F 2 transition located
at 614 nm, corresponding to the red emission, in good
accordance with the Judd-Ofelt theory [24]. Therefore,
strong red emission can be observed. The main excitation
peaks indicate the phosphor is very suitable for a color
converter using UV lights as the primary light source. It
can be used as a red phosphor excited by UV-LED chip
and would have applications in the solid-state lighting
field.
a) λ em = 614 nm b)
300 400 500 600 700
Wavelength (nm)
λ ex = 394 nm
3+
Figure 5. Photoluminescence spectra of Ba1.95MgSi2O7: Eu0.05 phosphor.
Color purity can be visualized in the chromaticity
diagram (Figure 6) as blue, red, and green regions,
using the color coordinates of the luminescent material
emission. So, from the luminescence emission spectra
of Ba 1.95MgSi 2O 7:Eu 0.05 3+ sample we obtained the
chromaticity coordiantes with the aid of the Spectra Lux
Software v.2.0 Beta [14]. For any given color there is
one setting for each three number X, Y and Z known as
254 Ceramics – Silikáty 55 (3) 251-255 (2011)
Relative intensity (a.u.)
λ ex = 465 nm
λ ex = 381 nm
λ ex = 362 nm
λ ex = 413 nm
800