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N. Tamai and S. Masuo
The photon correlation histogram indicates that the probability of the single-photon
emission increases when the center peak at delay time 0 ns is close to zero. To
analyze the photon correlation histogram quantitatively, the second-order correlation
function, g
(2) (0), was defined as the ratio of the center peak to the average number
of the other peaks. Thus, the g
(2) (0) value means that the probability of a singlephoton emission increases when g
(2) (0) is close to zero. In the case of emission
from a single QD, the g
(2) (0) value corresponds to BX / SX , where BX and SX
are quantum yields of the BX and SX emission, respectively. In the case of the
photon correlation histogram shown in Fig. 10.13d, the g
(2) (0) value was calculated
to be 0.14, indicating that the isolated single QD exhibited single-photon emission,
i.e., photon antibunching. PL decay curve of the single QD (Fig. 10.13g) was well
fitted using a single exponential decay function with a lifetime of 29.6 ns. These are
typical PL behavior of the single QD itself, which were dramatically modified by the
approach of the AuCube. The PL behavior of the single QD after the manipulation of
the AuCube is shown in Fig. 10.13b, e, and h. The maximum PL count from the single
QD increased from ca. 45 counts/ms to ca. 60 counts/ms. In the photon correlation
histogram, the center peak dramatically increased, and the g
(2) (0) values increased
to 0.97. This increase in the g
(2) (0) values indicated that the contribution of the BX
emission from the single QD was 6.9 times higher than that of the single QD before
the approach of the AuCube. In Fig. 10.13h, the PL was decayed rapidly, indicating
the radiative and/or nonradiative processes of the QD which was modified by the
AuCube. By the approach of the AuCube to the single QD, the PL intensity and the
contribution of the BX emission increased 1.3 times and 6.9 times, respectively, with a
shortening of the PL lifetime. The PL behavior of the single QD after separating the
AuCube is shown in Fig. 10.13c, f, and i. The PL intensity, photon antibunching
behavior, and decay curve were returned to original behavior, i.e., the emission
behavior of the single QD before the approach of the AuCube. The importance of
the present results is that the modification of the PL behavior was directly observed
accompanying the interaction between a single QD and an AuCube. To discuss
the mechanism of the modification, the enhancement factors of the radiative and
nonradiative rates were estimated from the modified PL intensity and the PL lifetime.
As a result, the enhancement factors for the radiative and nonradiative rates were
estimated to be 95 and 54 times, respectively [33]. These values indicated that the
proposed two mechanism, i.e., both the enhancement of the BX emission rate and
the quenching of the SX state, result in an increase in the contribution of the BX
emission upon the interaction of the QD with the AuCube. The present results directly
demonstrated that the emission photon statistics and PL intensity from a single QD
can be tuned by controlling the exciton relaxation processes using MNS.
N. Tamai and S. Masuo
The photon correlation histogram indicates that the probability of the single-photon
emission increases when the center peak at delay time 0 ns is close to zero. To
analyze the photon correlation histogram quantitatively, the second-order correlation
function, g
(2) (0), was defined as the ratio of the center peak to the average number
of the other peaks. Thus, the g
(2) (0) value means that the probability of a singlephoton emission increases when g
(2) (0) is close to zero. In the case of emission
from a single QD, the g
(2) (0) value corresponds to BX / SX , where BX and SX
are quantum yields of the BX and SX emission, respectively. In the case of the
photon correlation histogram shown in Fig. 10.13d, the g
(2) (0) value was calculated
to be 0.14, indicating that the isolated single QD exhibited single-photon emission,
i.e., photon antibunching. PL decay curve of the single QD (Fig. 10.13g) was well
fitted using a single exponential decay function with a lifetime of 29.6 ns. These are
typical PL behavior of the single QD itself, which were dramatically modified by the
approach of the AuCube. The PL behavior of the single QD after the manipulation of
the AuCube is shown in Fig. 10.13b, e, and h. The maximum PL count from the single
QD increased from ca. 45 counts/ms to ca. 60 counts/ms. In the photon correlation
histogram, the center peak dramatically increased, and the g
(2) (0) values increased
to 0.97. This increase in the g
(2) (0) values indicated that the contribution of the BX
emission from the single QD was 6.9 times higher than that of the single QD before
the approach of the AuCube. In Fig. 10.13h, the PL was decayed rapidly, indicating
the radiative and/or nonradiative processes of the QD which was modified by the
AuCube. By the approach of the AuCube to the single QD, the PL intensity and the
contribution of the BX emission increased 1.3 times and 6.9 times, respectively, with a
shortening of the PL lifetime. The PL behavior of the single QD after separating the
AuCube is shown in Fig. 10.13c, f, and i. The PL intensity, photon antibunching
behavior, and decay curve were returned to original behavior, i.e., the emission
behavior of the single QD before the approach of the AuCube. The importance of
the present results is that the modification of the PL behavior was directly observed
accompanying the interaction between a single QD and an AuCube. To discuss
the mechanism of the modification, the enhancement factors of the radiative and
nonradiative rates were estimated from the modified PL intensity and the PL lifetime.
As a result, the enhancement factors for the radiative and nonradiative rates were
estimated to be 95 and 54 times, respectively [33]. These values indicated that the
proposed two mechanism, i.e., both the enhancement of the BX emission rate and
the quenching of the SX state, result in an increase in the contribution of the BX
emission upon the interaction of the QD with the AuCube. The present results directly
demonstrated that the emission photon statistics and PL intensity from a single QD
can be tuned by controlling the exciton relaxation processes using MNS.