This subject provides comprehensive overview of the optical properties of the In1-xGaxP/ZnS CQDs.
The In1-xGaxP/ZnS (0 ≤ x ≤ 1) CQDs are successfully synthesized by hot-injection method and the ZnS shell is synthesized by simple injection of TOP, sulfur solution as a sulfur source. With various structural, elemental, and optical analysis techniques (XRD, ICP-MS, XPS, and TDPL), In1-
31
xGaxP/ZnS CQDs have alloy structure and also they have many defects as Ga ratio increase. The XRD patterns shift gradually from InP to GaP as In/Ga ratio change and so do XPS spectra. Also TEM images show In1-xGaxP/ZnS CQDs have sphere shape and similar particle size that can ignore
quantum confinement effect to analyze In/Ga ratio effect. As a result, the randomization of lattice is a main factor of decreasing PLQY and increasing shoulder peak. At In rich condition, there is no defect induced PL, but as Ga ratio increase, defect induced PL is occur and this can be figure out by TDPL.
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Figure 3.1 XRD patterns of In1-xGaxP/ZnS CQDs with different In/Ga ratio
30 40 50 60 70 80 90
2θ (degree)
Intensity (a.u)
InP _ PDF Number : 03-065-5740 GaP _ PDF Number : 01-071-4781 (GaIn)P2 _ PDF Number : 01-071-4504
30 40 50 60 70 80 90
Intensity (a.u)
2θ (degree)
InP _ PDF Number : 03-065-5740 GaP _ PDF Number : 01-071-4781 (GaIn)P2 _ PDF Number : 01-071-4504
30 40 50 60 70 80 90
Intensity (a.u)
2θ (degree)
InP _ PDF Number : 03-065-5740 GaP _ PDF Number : 01-071-4781 (GaIn)P2 _ PDF Number : 01-071-4504
30 40 50 60 70 80 90
Intensity (a.u)
InP _ PDF Number : 03-065-5740 GaP _ PDF Number : 01-071-4781 (GaIn)P2 _ PDF Number : 01-071-4504
2θ (degree)
30 40 50 60 70 80 90
2θ (degree)
InP _ PDF Number : 03-065-5740 GaP _ PDF Number : 01-071-4781 (GaIn)P2 _ PDF Number : 01-071-4504
Intensity (a.u)
30 40 50 60 70 80 90
Intensity (a.u)
2θ (degree) InP@ZnS1 In0.75Ga
0.25P@ZnS In0.50Ga0.50P@ZnS In0.25Ga
0.75P@ZnS GaP@ZnS
(a) (b)
(c)
(e)
(d)
(f)
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Figure 3.2 In/Ga ratio which is measured by ICP-MS
0.0 0.2 0.4 0.6 0.8 1.0
0.0 0.2 0.4 0.6 0.8
1.0 In
Ga
Ga ratio
In ratio
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Figure 3.3 HR-TEM image of In1-xGaxP/ZnS CQDs (a~e).
(a) (b)
(c) (d)
(e)
35
Figure 3.4 XPS analysis of In1-xGaxP/ZnS CQDs. (a) In 3d, (b) Ga 3d binding energy with different In/Ga ratio.
460 455 450 445 440
Binding Energy (eV)
Counts / s
30 27 24 21 18 15 12
In4d
Binding Energy (eV)
Counts / s
(a) (b)
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Figure 3.5 Solution UV-Vis spectra and PL spectra of In1-xGax/ZnS CQDs.
300 400 500 600 700 800 900
Intensity (a.u.)
Wavelength (nm)
InP@ZnSf In0.75Ga0.25P@ZnS In0.5Ga0.5P@ZnS In0.25Ga0.75P@ZnS GaP@ZnS
300 400 500 600 700 800 900 Wavelength (nm)
Intensity (a.u.)
InP@ZnSf In0.75Ga0.25P@ZnS In0.5Ga0.5P@ZnS In0.25Ga0.75P@ZnS GaP@ZnS
200 300 400 500 600 700 800
InP@ZnSf In0.85Ga0.15P@ZnS In0.63Ga0.37P@ZnS In0.45Ga0.55P@ZnS GaP@ZnS
Absorbance (a.u.)
Wavelength (nm)
(a) (b) (c)
37
Figure 3.6 Normalized Temperature dependent PL spectra of In1-xGax/ZnS CQDs.
400 500 600 700 800 900
Wavelength (nm)
Normalized Intensity (a.u.)
20K 30K 50K 70K 100K 120K 150K 200K 250K 300K
400 500 600 700 800 900
Wavelength (nm)
20K 30K 50K 70K 100K 120K 150K 200K 250K 300K
Normalized Intensity (a.u.)
400 500 600 700 800 900
Wavelength (nm)
Normalized Intensity (a.u.) 20K 30K
50K 70K 100K 120K 150K 200K 250K 300K
400 500 600 700 800 900
Normalized Intensity (a.u.) 20K 30K
50K 70K 100K 120K 150K 200K 250K 300K
Wavelength (nm)
400 500 600 700 800 900
Normalized Intensity (a.u.)
Wavelength (nm)
20K 30K 50K 70K 100K 120K 150K 200K 250K 300K
(a) (b)
(c) (d)
(e)
38
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