In this work, alkaline earth aluminate phosphors doped with rare-earth ions and manganese were
synthesized using combustion method. Several characterization techniques were used to study
the structural and luminescent properties of the as-synthesized phosphors, namely X-ray
diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray energy Dispersive
Spectroscopy (EDS), Ultraviolet-Visible (UV-Vis) Spectroscopy, Photoluminescence (PL), and
Thermoluminescence (TL). The structural properties were studied by collecting the XRD
patterns of the samples using an X'Pert PRO PANalytical diffractometer with CuKα at λ =
0.15405 nm. The particle morphologies of the as-synthesized powder phosphors were
investigated using a JEOL JSM-7500F field-emission scanning electron microscope (FE-SEM). The
optical properties of the phosphors were studied using Perkin-Elmer Lambda 750s UV-Vis
spectrometer, Jobin Yvon/SPEX FluoroLog spectrofluorometer (Model FL-1040) and Riso
TL/OSL reader (Model DA-20).
The as-prepared SrAl2O4:Eu
2+
; SrAl2O4:Dy
3+; SrAl2O4:Mn
2+; phosphors were synthesized at an
initiating temperature of 600 oC. The XRD patterns were consistent with the low temperature
monoclinic structure of SrAl2O4 for all the as-synthesized phosphor powders. SEM
measurements showed nano-rod like particles. The SrAl2O4:Eu
2+
; SrAl2O4:Dy
3+; SrAl2O4:Mn
2+
samples were excited using a 450 W Xenon light source at 364 nm, 390 nm, and 426 nm
respectively. A broad blue emission peak at 500 nm shown by the SrAl2O4:Eu
2+ sample is
attributed to the 6 1 7 4f 5d 4f transition of the Eu
2+
ion. Also, the red sharp emission lines due
to the 4f-4f transition of the Eu
3+
were observed.
SrAl2O4:Dy3+ samples exhibited blue, green, and red emissions which can be atributed to the
4 6
9/2 15/2 F H ,4 6
9/2 13/2 F H , and 4 6
9 11
2 2
F H transitions of Dy
3+
ions respectively. The
two broad emissions (green at 513 nm and red at 650 nm) shown by 2+
0.98 2 4 0.02 Sr Al O :Mn
sample can be atributed to the 4 4 6 6
1 1 T ( G) A ( S) transition of the Mn
2+
ion in the sample.
The SrAl2O4:Eu
2+
, Dy
3+
; SrAl2O4:Eu
2+, Mn
2+
; SrAl2O4:Dy
3+, Mn
2+; and SrAl2O4:Eu
2+
,Mn
2+,
Dy
3+
phosphors were synthesized by combustion method at an initiating temperature of 600 oC.
The blue emissions were observed in all the samples except SrAl2O4:Eu
2+
,Mn
2+, Dy
3+
sample.
The SrAl2O4:Eu
2+
,Mn
2+, Dy
3+
phosphor showed the longest afterglow intensity.
The BaAl2O4 doped with Eu
2+
, Mn
2+
and Dy
3+
phosphors synthesized at an initiating
temperature of 600 oC using combustion method. The XRD patterns confirmed the hexagonal
structure of BaAl2O4 in all the as-synthesized samples. A broad blue emission of the
BaAl2O4:Eu
2+
sample at 490 nm is attributed to the 6 1 7 4f 5d 4f transition of the Eu
2+
ion in
the sample. A red emission peak observed at 611 nm is due to the 4f - 4f transition of un-reduced
Eu
3+
ions during the combustion reaction. A blue emission at 482 nm, a green emission at 575
nm, and a red emission at 663 nm of the BaAl2O4:Dy
3+
sample can be associated with
4 6
9/2 15/2 F H ,4 6
9/2 13/2 F H , and 4 6
9 11
2 2
F H transitions of the Dy
3+
ions respectively. The
green emission peaks exhibited by BaAl2O4:Mn
2+
sample at 512 nm is due to the
4 4 6 6
1 1 T ( G) A ( S) transitions of the Mn
2+
ions.
Barium aluminate phosphors doped with different concentrations of Dy
3+ ion were synthesized
by combustion method at an initiating temperature of 600 oC. The XRD patterns confirmed the
hexagonal structure of BaAl2O4. The emission peaks observed at 482 nm, 575 nm, and 663 nm
are due to4 6
9/2 15/2 F H ,4 6
9/2 13/2 F H and 4 6
9 11
2 2
F H transitions of Dy
3+
ion respectively.
The PL measurements also confirmed the quenching of luminescence at higher concentrations of
the Dy
3+
ion. The UV-Vis measurements has confirmed the increase in the band-gap of the
BaAl2O4 sample followed by a decrease and an increase again as doping concentration of the
Dy
3+
increased.
The X-ray diffraction patterns of the Ca0.97M0.3Al2O4:Eu
2+
, Dy
3+
(M = Ba, Mg, and Sr) powder
samples prepared by combustion method confirms the monoclinic structure of CaAl2O4 in all
samples. A broad emission peak at 490 nm for both Ba
2+
and Mg
2+
substituted samples and the one for Sr
2+
substituted sample at 485nm are attributed to the 6 1 7 4f 5d 4f transition of the
Eu
2+
. The decay curves confirmed that the Mg
2+
substituted sample has a longer persistence
(phosphorescence) than all the other samples. / Physics / M. Sc. (Physics)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:unisa/oai:uir.unisa.ac.za:10500/20709 |
| Date | January 2015 |
| Creators | Colen, Manaka Mmakgabo |
| Contributors | Mothudi, B. M., Dhlamini, M. S. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | 1 online resource (xiv, 106 leaves) : color illustrations |
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