13 Controlling Optical Properties of Multinary Quantum Dots …
229
band-edge peaks clearly appeared as shown in Fig. 13.4b. The FWHMs of bandedge emission peaks were ca. 40 nm (180 meV), being much narrower than those
of defect-site emission peaks, 100 ~ 200 nm (Figs. 13.1 and 13.2). The position of
the PL peak was also blue-shifted from 590 to 500 nm with an increase in the E g
of QDs. The PL QYs of AIGS@GaS x QDs were relatively high, the optimal value
being 28% for 530-nm band-edge emission with AIGS@GaS x QDs prepared with
In/(In + Ga) = 0.40.
PL peaks of AgInS 2 -based QDs were narrowed by removing defect sites causing
broad PL peaks both via precise tuning of the reaction conditions and via surface
coating with a GaS x shell. However, the thus-obtained band-edge emission peak still
had a relatively large width for the application to optical devices. Single-particle
spectroscopy enables clarification of the origins of PL peak broadening. We found
that the band-edge emission peaks from single AIS QDs were much narrower than
those observed in the ensemble measurement, in which the peak widths (FWHM)
were ca. 20 nm (73 meV), while the peak position fluctuated greatly from particle to
particle between ca. 600 nm (2.0 eV) and ca. 550 nm(2.3 eV). These results indicated
that the ensemble PL peaks were inhomogeneously broadened, probably due to the
size and composition variations of individual QDs. Thus, we can conclude that the
band-edge PL peak in the ensemble measurement of AgInS 2 -based QDs will be
potentially further narrowed by reducing their inhomogeneity.
13.2.2 Controllable PL Peak of Zn-Ag-in-Te QDs
in the Near-IR Region
Tunable optical properties in the near-IR wavelength region are useful for developing novel QD-based photovoltaic systems. We successfully prepared near-IRlight-responsive QDs of high quality by making a solid solution between ZnTe
and AgInTe 2 , (AgIn) x Zn 2(1-x) Te 2 (ZAITe) [17], in place of multinary metal sulfides.
ZAITe has a widely tunable E g because bulk E g s of AgInTe 2 and ZnTe are 1.0 and
2.3 eV, respectively. The metal precursors of corresponding metal acetates were
reacted with trioctylphosphine telluride in DDT at 180 °C for 180 min with the
ZAITe composition being modified by changing the metal precursor ratio, Ag:In:Zn
= x:x:2(1−x) (0.25 < x<1). The thus-obtained ZAITe QDs had a rod-like structure
as shown in Fig. 13.5a and 13.5b, the dimensions of which were ca. 16 ~ 18 nm in
length and ca. 4 ~ 5 nm in width, regardless of the x values. Each QD was a single
crystal grown along the c-axis of a wurtzite structure without a grain boundary.
As shown in Fig. 13.5c, the ZAITe QDs had clear exciton peaks in the absorption
spectra, the peak position of which was in the near-IR wavelength region and was
shifted from 965 to 710 nm with an increase in the Zn fraction, that is, with a decrease
in the x value. The E g of ZAITe QDs, determined from the absorption onset, was
enlarged from 1.2 to 1.6 eV by increasing the Zn content. Furthermore, band-edge
emission peaks appeared at around the corresponding absorption onsets. The PL
229
band-edge peaks clearly appeared as shown in Fig. 13.4b. The FWHMs of bandedge emission peaks were ca. 40 nm (180 meV), being much narrower than those
of defect-site emission peaks, 100 ~ 200 nm (Figs. 13.1 and 13.2). The position of
the PL peak was also blue-shifted from 590 to 500 nm with an increase in the E g
of QDs. The PL QYs of AIGS@GaS x QDs were relatively high, the optimal value
being 28% for 530-nm band-edge emission with AIGS@GaS x QDs prepared with
In/(In + Ga) = 0.40.
PL peaks of AgInS 2 -based QDs were narrowed by removing defect sites causing
broad PL peaks both via precise tuning of the reaction conditions and via surface
coating with a GaS x shell. However, the thus-obtained band-edge emission peak still
had a relatively large width for the application to optical devices. Single-particle
spectroscopy enables clarification of the origins of PL peak broadening. We found
that the band-edge emission peaks from single AIS QDs were much narrower than
those observed in the ensemble measurement, in which the peak widths (FWHM)
were ca. 20 nm (73 meV), while the peak position fluctuated greatly from particle to
particle between ca. 600 nm (2.0 eV) and ca. 550 nm(2.3 eV). These results indicated
that the ensemble PL peaks were inhomogeneously broadened, probably due to the
size and composition variations of individual QDs. Thus, we can conclude that the
band-edge PL peak in the ensemble measurement of AgInS 2 -based QDs will be
potentially further narrowed by reducing their inhomogeneity.
13.2.2 Controllable PL Peak of Zn-Ag-in-Te QDs
in the Near-IR Region
Tunable optical properties in the near-IR wavelength region are useful for developing novel QD-based photovoltaic systems. We successfully prepared near-IRlight-responsive QDs of high quality by making a solid solution between ZnTe
and AgInTe 2 , (AgIn) x Zn 2(1-x) Te 2 (ZAITe) [17], in place of multinary metal sulfides.
ZAITe has a widely tunable E g because bulk E g s of AgInTe 2 and ZnTe are 1.0 and
2.3 eV, respectively. The metal precursors of corresponding metal acetates were
reacted with trioctylphosphine telluride in DDT at 180 °C for 180 min with the
ZAITe composition being modified by changing the metal precursor ratio, Ag:In:Zn
= x:x:2(1−x) (0.25 < x<1). The thus-obtained ZAITe QDs had a rod-like structure
as shown in Fig. 13.5a and 13.5b, the dimensions of which were ca. 16 ~ 18 nm in
length and ca. 4 ~ 5 nm in width, regardless of the x values. Each QD was a single
crystal grown along the c-axis of a wurtzite structure without a grain boundary.
As shown in Fig. 13.5c, the ZAITe QDs had clear exciton peaks in the absorption
spectra, the peak position of which was in the near-IR wavelength region and was
shifted from 965 to 710 nm with an increase in the Zn fraction, that is, with a decrease
in the x value. The E g of ZAITe QDs, determined from the absorption onset, was
enlarged from 1.2 to 1.6 eV by increasing the Zn content. Furthermore, band-edge
emission peaks appeared at around the corresponding absorption onsets. The PL