Supporting Information Room Temperature Single ... AWS
Supporting Information
Room Temperature Single-Photon Emission from Individual Perovskite Quantum Dots Young-Shin Park, †,‡ Shaojun Guo,† Nikolay Makarov, † and Victor I. Klimov† †
Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
‡
Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico 87131, USA.
1
1. Absorption and photoluminescence (PL) spectra
Figure S1. (a) Transmission electron microscopy (TEM) images of QDs of CsPbBr3 (mean size 9.3 ± 0.9 nm), CsPbBrxI3-x (x = 1.5, 10.7 ± 1.1 nm), and CsPbI3 (11.2 ± 0.7 nm). (b) Absorption and PL spectra measured for solution samples. PL peak positions are 510 nm for the CsPbBr3 QDs, 585 nm for the CsPbBrxI3-x QDs, and 683 nm for the CsPbI3 QDs, respectively. Linewidths, evaluated in terms of a full width at half maximum (FWHM), are 22, 32, and 34 nm, respectively. PL quantum yields (QYs) are indicated in the figure. The absorptivity is shown in terms of absorption cross-sections derived from pump-intensitydependent PL dynamics (see Section 4). The PL spectra and QY measurements were conducted using continuous wave excitation of low intensity for which the average number of electron-hole pairs per QD was less than 0.001, as evaluated based on the measured absorption cross-sections and single-exciton lifetimes (excitation wavelengths are indicate in the main text).
2
2. Measurements of irreversible photodegradation
Figure S2. (a) PL spectra of a single CsPbI3 QD measured at time t = 0 s (bottom) and t = 300 s (top) without exposure to laser light between the measurements. The lack of changes in either PL intensity or peak position suggests that QD degradation is a photoinduced process. (b) Temporal evolution of the single-dot PL spectra monitored for 80 s of continuous exposure to laser light with intensity Ip = 420 W/cm2. (c) The PL intensity and peak position as a function of time (based on the data in ‘b’). (d) & (e) Same for the single CsPbBr3 QD; Ip = 300 W/cm2.
3
3. PL blinking of individual CsPbBr3 and CsPbBrxI3-x QDs
Figure S3. (a) Blinking trace and (b) PL spectra of a single CsPbBrxI3-x QD (x = 1.3); black and blue traces in ‘b’ correspond to the beginning and the end of the measured trajectory. Bin size is 10ms. (c) & (d) Same for a single CsPbBr3 QD. The QD is completely bleached at the end of the trajectory, which precluded the measurement of the final PL spectrum. The two QDs shown in ‘a’ and ‘c’ exhibited the greatest stability among all tested dots of these compositions; all other QDs were completely “bleached” during much less than a minute.
4
4. Pump-intensity dependence of PL dynamics for the CsPbI3 QD solution sample
Figure S4. (a) Pump-fluence dependence of time-resolved PL for CsPbI3 QDs dispersed in hexane. Pump fluence is evaluated in terms of the average per-dot excitonic occupancy 〈N〉 generated at t = 0. These measurements were conducted with 50-ps resolution using a superconducting nanowire single-photon detector. (b) PL decay traces normalized at long times where dynamics are solely due to single excitons. The early time fast decay component emerging at higher pump fluences is due to Auger recombination of biexcitons. (c) Biexciton dynamics isolated by subtracting the contribution from the single-exciton decay measured with 〈N〉 = 0.006 (black line in ‘a’). Single exponential fits yield the mean value of the biexciton lifetime τXX = 93 ps. (d) The measured pump-fluence-dependence of the amplitude of the slow single-exciton component derived from PL dynamics in ‘a’ (squares) along with a fit obtained assuming Poisson statistics of photon absorption events (line). The fit yields absorption cross-section σ = 1 ×10-14 cm2 at λ = 400 nm.
5
5. Quantitative analysis of photocharging First, we find a functional dependence of the PL intensity (IPL) on PL lifetime (τPL) for PL fluctuations resulting from the fluctuation of the degree of charging (0 ≤ f ≤ 1). We assume that the PL intensity varies linearly with f as: IPL = IX + (IX* - IX) f,
(1)
where IX and IX* are the PL intensity of the neutral (X) and charged (X*) excitons that correspond to the ON and OFF levels in the PL intensity trajectories. This expression yields the expected intensity values in the limits of no charging (f = 0) and permanent charging (f = 1) when IPL = IX and IX*, respectively. To account for a weak curvature of measured FLIDS, we describe τPL as:
τPL = τX + (τX* - τX) f γ
(2)
where τX and τX* are the neutral and charged exciton lifetimes. By varying f from 0 to 1, we obtain a “charging trajectory” in the IPL-τPL space, which we then compare to the measured FLIDs. We observe that we can closely describe the measurements with γ = 1.2, which yields the charging trajectory shown in Figs. 3c-f by the white line. Next, on the basis of the measured FLIDs, we quantify the fraction of time spent by the QD in the OFF state (fOFF) for a given pump intensity. For this purpose, we slice the τPL axis into narrow ΔτPL intervals and “project” all events from a given interval onto the charging trajectory. This yields the probability histogram for the degree of charging as shown in the example of Fig. S5. Then, we calculate the average value of f, which we assign to fOFF.
6
Figure S5. A probability histogram of the degree of charging obtained based on the FLID in Fig. 3c in the main text.
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6. ON- and OFF-time probability distributions for CsPbBr3 and CsPbBrxI3-x QDs
Figure S6. (a) The ON-time and (b) the OFF-time probability distribution for a single CsPbBrxI3-x QD (x = 1.3). (c) & (d) Same for a single CsPbBr3 QD.
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Room Temperature Single-Photon Emission from Individual Perovskite Quantum Dots Young-Shin Park, †,‡ Shaojun Guo,† Nikolay Makarov, † and Victor I. Klimov† †
Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
‡
Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico 87131, USA.
1
1. Absorption and photoluminescence (PL) spectra
Figure S1. (a) Transmission electron microscopy (TEM) images of QDs of CsPbBr3 (mean size 9.3 ± 0.9 nm), CsPbBrxI3-x (x = 1.5, 10.7 ± 1.1 nm), and CsPbI3 (11.2 ± 0.7 nm). (b) Absorption and PL spectra measured for solution samples. PL peak positions are 510 nm for the CsPbBr3 QDs, 585 nm for the CsPbBrxI3-x QDs, and 683 nm for the CsPbI3 QDs, respectively. Linewidths, evaluated in terms of a full width at half maximum (FWHM), are 22, 32, and 34 nm, respectively. PL quantum yields (QYs) are indicated in the figure. The absorptivity is shown in terms of absorption cross-sections derived from pump-intensitydependent PL dynamics (see Section 4). The PL spectra and QY measurements were conducted using continuous wave excitation of low intensity for which the average number of electron-hole pairs per QD was less than 0.001, as evaluated based on the measured absorption cross-sections and single-exciton lifetimes (excitation wavelengths are indicate in the main text).
2
2. Measurements of irreversible photodegradation
Figure S2. (a) PL spectra of a single CsPbI3 QD measured at time t = 0 s (bottom) and t = 300 s (top) without exposure to laser light between the measurements. The lack of changes in either PL intensity or peak position suggests that QD degradation is a photoinduced process. (b) Temporal evolution of the single-dot PL spectra monitored for 80 s of continuous exposure to laser light with intensity Ip = 420 W/cm2. (c) The PL intensity and peak position as a function of time (based on the data in ‘b’). (d) & (e) Same for the single CsPbBr3 QD; Ip = 300 W/cm2.
3
3. PL blinking of individual CsPbBr3 and CsPbBrxI3-x QDs
Figure S3. (a) Blinking trace and (b) PL spectra of a single CsPbBrxI3-x QD (x = 1.3); black and blue traces in ‘b’ correspond to the beginning and the end of the measured trajectory. Bin size is 10ms. (c) & (d) Same for a single CsPbBr3 QD. The QD is completely bleached at the end of the trajectory, which precluded the measurement of the final PL spectrum. The two QDs shown in ‘a’ and ‘c’ exhibited the greatest stability among all tested dots of these compositions; all other QDs were completely “bleached” during much less than a minute.
4
4. Pump-intensity dependence of PL dynamics for the CsPbI3 QD solution sample
Figure S4. (a) Pump-fluence dependence of time-resolved PL for CsPbI3 QDs dispersed in hexane. Pump fluence is evaluated in terms of the average per-dot excitonic occupancy 〈N〉 generated at t = 0. These measurements were conducted with 50-ps resolution using a superconducting nanowire single-photon detector. (b) PL decay traces normalized at long times where dynamics are solely due to single excitons. The early time fast decay component emerging at higher pump fluences is due to Auger recombination of biexcitons. (c) Biexciton dynamics isolated by subtracting the contribution from the single-exciton decay measured with 〈N〉 = 0.006 (black line in ‘a’). Single exponential fits yield the mean value of the biexciton lifetime τXX = 93 ps. (d) The measured pump-fluence-dependence of the amplitude of the slow single-exciton component derived from PL dynamics in ‘a’ (squares) along with a fit obtained assuming Poisson statistics of photon absorption events (line). The fit yields absorption cross-section σ = 1 ×10-14 cm2 at λ = 400 nm.
5
5. Quantitative analysis of photocharging First, we find a functional dependence of the PL intensity (IPL) on PL lifetime (τPL) for PL fluctuations resulting from the fluctuation of the degree of charging (0 ≤ f ≤ 1). We assume that the PL intensity varies linearly with f as: IPL = IX + (IX* - IX) f,
(1)
where IX and IX* are the PL intensity of the neutral (X) and charged (X*) excitons that correspond to the ON and OFF levels in the PL intensity trajectories. This expression yields the expected intensity values in the limits of no charging (f = 0) and permanent charging (f = 1) when IPL = IX and IX*, respectively. To account for a weak curvature of measured FLIDS, we describe τPL as:
τPL = τX + (τX* - τX) f γ
(2)
where τX and τX* are the neutral and charged exciton lifetimes. By varying f from 0 to 1, we obtain a “charging trajectory” in the IPL-τPL space, which we then compare to the measured FLIDs. We observe that we can closely describe the measurements with γ = 1.2, which yields the charging trajectory shown in Figs. 3c-f by the white line. Next, on the basis of the measured FLIDs, we quantify the fraction of time spent by the QD in the OFF state (fOFF) for a given pump intensity. For this purpose, we slice the τPL axis into narrow ΔτPL intervals and “project” all events from a given interval onto the charging trajectory. This yields the probability histogram for the degree of charging as shown in the example of Fig. S5. Then, we calculate the average value of f, which we assign to fOFF.
6
Figure S5. A probability histogram of the degree of charging obtained based on the FLID in Fig. 3c in the main text.
7
6. ON- and OFF-time probability distributions for CsPbBr3 and CsPbBrxI3-x QDs
Figure S6. (a) The ON-time and (b) the OFF-time probability distribution for a single CsPbBrxI3-x QD (x = 1.3). (c) & (d) Same for a single CsPbBr3 QD.
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