200
S. Ghimire et al.
‘ON’ and dark ‘OFF’ events known as PL intermittency or blinking. This is attributed
to the random charging by photoionization and neutralization or discharging of the
QD. The blinking behavior in QDs is often described as A-type and B-type [21].
In A-type blinking, the ‘OFF’ state is associated with the decrease in PL lifetime,
whereas the carrier-recombination rates are not affected by the ‘OFF’ or the ‘ON’
states in B-type blinking. The short PL lifetime observed during the ‘OFF’ state in
A-type blinking is attributed to the formation of a charged excitonic state called a
trion (X
− ) which promotes the mono-exponential nonradiative Auger-type carrier
recombination in QDs. On the other hand, B-type blinking mostly depends on the
activation and deactivation of the traps or its recombination centers which leads to
the ‘ON’ and ‘OFF’ states, respectively.
Apart from the QDs, diverse stochastic emission behavior has been observed in the
case of perovskite single nanocrystals, microcrystals, and thin films [22–27]. Some
perovskite single-emitters have shown blinking with two-state fluctuations between
‘ON’ and ‘OFF’ events [24, 25, 27], which is similar to the case of chalcogenide
QD and is ascribed to the process of photocharging and neutralization. Semiconductor nanocrystals or QDs show various interesting optoelectronic properties in the
isolated forms. On the other hand, multi-state PL blinking has also been reported
from the nanocrystals, microcrystals, and films of lead halide perovskite [22, 23,
26]. An early report on PL blinking in MAPbI 3 PNCs and microcrystals has shown
that the chemical and structural properties of material are responsible for the multistate stochastic emission behavior [22]. This is explained through two mechanisms,
namely the quenching-site and the emitting-site model, which is shown in Fig. 11.2.
In emitting-site model, as shown in Fig. 11.2a, the emitters are at the either end of
the nanocrystal which randomly get charged and discharged leading to the ‘ON’ and
‘OFF’ states, respectively. Quenching-site model (Fig. 11.2b) considers the whole
nanocrystal as an emissive site, where the emission localization position and center of
the nanocrystals lie at the same point. Quenchers in quenching-site model act as traps
which are present at the either end of the nanocrystal and deactivate the electrons
and holes during the diffusion, resulting in the ‘OFF’ state. An interesting behavior
of PL blinking in lead halide perovskites is that, unlike lead chalcogenide QDs,
the multi-state PL fluctuations in these semiconductor materials is suppressed under
high-intensity of excitation, which on the other hand becomes more intense at lowintensity of excitation. Figure 11.3a shows the excitation laser intensity-dependent
PL blinking in MAPbI 3 PNCs at the ambient environment. The suppression of PL
blinking in such perovskite samples at high-intensity excitation is attributed to the
decrease in efficiency of active quenchers to trap large number of charges. Alternately,
more emitting sites are generated at high-intensity excitation, resulting in the averaged PL intensity over many emitting sites. Nevertheless, as shown in Fig. 11.3a(i)
and b(i), photobleaching cannot be ruled out at high-intensity excitation under the
ambient atmosphere [22, 25, 27].
S. Ghimire et al.
‘ON’ and dark ‘OFF’ events known as PL intermittency or blinking. This is attributed
to the random charging by photoionization and neutralization or discharging of the
QD. The blinking behavior in QDs is often described as A-type and B-type [21].
In A-type blinking, the ‘OFF’ state is associated with the decrease in PL lifetime,
whereas the carrier-recombination rates are not affected by the ‘OFF’ or the ‘ON’
states in B-type blinking. The short PL lifetime observed during the ‘OFF’ state in
A-type blinking is attributed to the formation of a charged excitonic state called a
trion (X
− ) which promotes the mono-exponential nonradiative Auger-type carrier
recombination in QDs. On the other hand, B-type blinking mostly depends on the
activation and deactivation of the traps or its recombination centers which leads to
the ‘ON’ and ‘OFF’ states, respectively.
Apart from the QDs, diverse stochastic emission behavior has been observed in the
case of perovskite single nanocrystals, microcrystals, and thin films [22–27]. Some
perovskite single-emitters have shown blinking with two-state fluctuations between
‘ON’ and ‘OFF’ events [24, 25, 27], which is similar to the case of chalcogenide
QD and is ascribed to the process of photocharging and neutralization. Semiconductor nanocrystals or QDs show various interesting optoelectronic properties in the
isolated forms. On the other hand, multi-state PL blinking has also been reported
from the nanocrystals, microcrystals, and films of lead halide perovskite [22, 23,
26]. An early report on PL blinking in MAPbI 3 PNCs and microcrystals has shown
that the chemical and structural properties of material are responsible for the multistate stochastic emission behavior [22]. This is explained through two mechanisms,
namely the quenching-site and the emitting-site model, which is shown in Fig. 11.2.
In emitting-site model, as shown in Fig. 11.2a, the emitters are at the either end of
the nanocrystal which randomly get charged and discharged leading to the ‘ON’ and
‘OFF’ states, respectively. Quenching-site model (Fig. 11.2b) considers the whole
nanocrystal as an emissive site, where the emission localization position and center of
the nanocrystals lie at the same point. Quenchers in quenching-site model act as traps
which are present at the either end of the nanocrystal and deactivate the electrons
and holes during the diffusion, resulting in the ‘OFF’ state. An interesting behavior
of PL blinking in lead halide perovskites is that, unlike lead chalcogenide QDs,
the multi-state PL fluctuations in these semiconductor materials is suppressed under
high-intensity of excitation, which on the other hand becomes more intense at lowintensity of excitation. Figure 11.3a shows the excitation laser intensity-dependent
PL blinking in MAPbI 3 PNCs at the ambient environment. The suppression of PL
blinking in such perovskite samples at high-intensity excitation is attributed to the
decrease in efficiency of active quenchers to trap large number of charges. Alternately,
more emitting sites are generated at high-intensity excitation, resulting in the averaged PL intensity over many emitting sites. Nevertheless, as shown in Fig. 11.3a(i)
and b(i), photobleaching cannot be ruled out at high-intensity excitation under the
ambient atmosphere [22, 25, 27].