13 Controlling Optical Properties of Multinary Quantum Dots …
225
increase in the DDT content decreased the particle size: The average size (d ave ) of
ZAIS QDs prepared with x = 0.5 was increased from 3.9 to 8.5 nm with a reduction
in the DDT content from 8.7 to 0 vol.%, and the particle composition was almost
constant at Ag:In:Zn = 0.25:0.30:0.45, being slightly In-rich and Zn-deficient. Thus,
the present method enabled independent control of the size and chemical composition
of spherical ZAIS QDs.
Figure 13.1 shows the absorption and PL spectra of ZAIS QDs with different
chemical compositions and sizes. ZAIS QDs exhibited absorption spectra in a wide
visible light region, the onset wavelength being blue-shifted with a decrease in d ave
(Fig. 13.1a) or with a decrease in the x value (Fig. 13.1c). These results indicated
that the E g of ZAIS QDs could be two-dimensionally controlled by changes in the
particle size and chemical composition. A broad PL peak, the full width at halfmaximum intensity (FWHM) of which was ca. 100 ~ 200 nm, was observed in the
PL spectra shown Fig. 13.1b and d for each kind of ZAIS QDs. The broadness of the
peak width arose from donor–acceptor pair (DAP) radiative recombination of trapped
carriers, not from band-to-band recombination of charge carriers, that is, band-edge
recombination. The PL peak wavelength was also shifted to a shorter wavelength
with an increase in the E g , indicating that the PL color was widely tunable from deep
red to green. The highest PL quantum yield (QY) of 79% for 630-nm emission was
obtained with ZAIS QDs of 5.7 nm in d ave prepared with x = 0.5.
Absorbance
(Normalized)
4.7
8.5
5.0
5.7
d ave = 3.9 nm
6.9
(b)
400 500 600 700 800 900 1000
PL Intensity
(Normalized)
Wavelength / nm
6.9
5.7
d ave = 5.0 nm
4.7
3.9
8.5
(a)
400 500 600 700 800 900 1000
PL Intensity
(Normalized)
Wavelength / nm
1.0
x = 0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Absorbance
(Normalized)
1.0
x = 0.1
0.9
0.8
0.7
0.6
0.2
0.3
0.4 0.5
(c)
(d)
Fig. 13.1 Absorption spectra (a, c) and PL spectra (b, d) of spherical ZAIS QDs in chloroform.
Samples are (a, b) ZAIS QDs of x = 0.5 with various sizes and (c, d) ZAIS QDs of ca. 5.5 nm in
d ave with different x values. Reprinted with permission from ref. [13]
225
increase in the DDT content decreased the particle size: The average size (d ave ) of
ZAIS QDs prepared with x = 0.5 was increased from 3.9 to 8.5 nm with a reduction
in the DDT content from 8.7 to 0 vol.%, and the particle composition was almost
constant at Ag:In:Zn = 0.25:0.30:0.45, being slightly In-rich and Zn-deficient. Thus,
the present method enabled independent control of the size and chemical composition
of spherical ZAIS QDs.
Figure 13.1 shows the absorption and PL spectra of ZAIS QDs with different
chemical compositions and sizes. ZAIS QDs exhibited absorption spectra in a wide
visible light region, the onset wavelength being blue-shifted with a decrease in d ave
(Fig. 13.1a) or with a decrease in the x value (Fig. 13.1c). These results indicated
that the E g of ZAIS QDs could be two-dimensionally controlled by changes in the
particle size and chemical composition. A broad PL peak, the full width at halfmaximum intensity (FWHM) of which was ca. 100 ~ 200 nm, was observed in the
PL spectra shown Fig. 13.1b and d for each kind of ZAIS QDs. The broadness of the
peak width arose from donor–acceptor pair (DAP) radiative recombination of trapped
carriers, not from band-to-band recombination of charge carriers, that is, band-edge
recombination. The PL peak wavelength was also shifted to a shorter wavelength
with an increase in the E g , indicating that the PL color was widely tunable from deep
red to green. The highest PL quantum yield (QY) of 79% for 630-nm emission was
obtained with ZAIS QDs of 5.7 nm in d ave prepared with x = 0.5.
Absorbance
(Normalized)
4.7
8.5
5.0
5.7
d ave = 3.9 nm
6.9
(b)
400 500 600 700 800 900 1000
PL Intensity
(Normalized)
Wavelength / nm
6.9
5.7
d ave = 5.0 nm
4.7
3.9
8.5
(a)
400 500 600 700 800 900 1000
PL Intensity
(Normalized)
Wavelength / nm
1.0
x = 0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Absorbance
(Normalized)
1.0
x = 0.1
0.9
0.8
0.7
0.6
0.2
0.3
0.4 0.5
(c)
(d)
Fig. 13.1 Absorption spectra (a, c) and PL spectra (b, d) of spherical ZAIS QDs in chloroform.
Samples are (a, b) ZAIS QDs of x = 0.5 with various sizes and (c, d) ZAIS QDs of ca. 5.5 nm in
d ave with different x values. Reprinted with permission from ref. [13]