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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 6 — Mar. 25, 2013
  • pp: 7419–7426
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Disentangling the effects of clustering and multi-exciton emission in second-order photon correlation experiments

Benjamin D. Mangum, Yagnaseni Ghosh, Jennifer A. Hollingsworth, and Han Htoon  »View Author Affiliations


Optics Express, Vol. 21, Issue 6, pp. 7419-7426 (2013)
http://dx.doi.org/10.1364/OE.21.007419


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Abstract

In single particle spectroscopy, the degree of observed fluorescence anti-bunching in a second-order cross correlation experiment is indicative of its bi-exciton quantum yield and whether or not a particle is well isolated. Advances in quantum dot synthesis have produced single particles with bi-exciton quantum yields approaching unity. Consequently, this creates uncertainty as to whether a particle has a high bi-exciton quantum yield or if it exists as a cluster. We report on a time-gated anti-bunching technique capable of determining the relative contributions of both multi-exciton emission and clustering effects. In this way, we can now unambiguously determine if a particle is single. Additionally, this time-gated anti-bunching approach provides an accurate way for the determination of bi-exciton lifetime with minimal contribution from higher order multi-exciton states.

© 2013 OSA

1. Introduction

The second-order photon cross correlation function, g(2)(τ), plays a critical role in characterizing the photon emission statistics of nanoscale light emitters including single molecules [1

1. F. Treussart, A. Clouqueur, C. Grossman, and J.-F. Roch, “Photon antibunching in the fluorescence of a single dye molecule embedded in a thin polymer film,” Opt. Lett. 26(19), 1504–1506 (2001). [CrossRef] [PubMed]

3

3. B. Lounis and W. E. Moerner, “Single photons on demand from a single molecule at room temperature,” Nature 407(6803), 491–493 (2000). [CrossRef] [PubMed]

], quantum dots [4

4. P. Michler, A. Kiraz, C. Becher, W. V. Schoenfeld, P. M. Petroff, L. Zhang, E. Hu, and A. Imamoglu, “A quantum dot single-photon turnstile device,” Science 290(5500), 2282–2285 (2000). [CrossRef] [PubMed]

,5

5. P. Michler, A. Imamoglu, M. D. Mason, P. J. Carson, G. F. Strouse, and S. K. Buratto, “Quantum correlation among photons from a single quantum dot at room temperature,” Nature 406(6799), 968–970 (2000). [CrossRef] [PubMed]

], carbon nanotubes [6

6. A. Högele, C. Galland, M. Winger, and A. Imamoğlu, “Photon antibunching in the photoluminescence spectra of a single carbon nanotube,” Phys. Rev. Lett. 100(21), 217401 (2008). [CrossRef] [PubMed]

], and diamond nanocrystals [7

7. C. Kurtsiefer, S. Mayer, P. Zarda, and H. Weinfurter, “Stable solid-state source of single photons,” Phys. Rev. Lett. 85(2), 290–293 (2000). [CrossRef] [PubMed]

9

9. R. Brouri, A. Beveratos, J.-P. Poizat, and P. Grangier, “Photon antibunching in the fluorescence of individual color centers in diamond,” Opt. Lett. 25(17), 1294–1296 (2000). [CrossRef] [PubMed]

]. It is widely used to test the correlation of intensities on two different photon detectors in a Hanburry Brown and Twiss configuration [10

10. W. Becker, Advanced Time-Correlated Single Photon Counting Techniques Chemical Physics (Springer, 2005).

]. In a pulsed laser experiment, it is well known that measuring a single quantum emitter will result in photon anti-bunching, which is signified by the disappearance of a peak at zero time delay. This arises from the fact that a single quantum emitter can only emit a single photon per excitation pulse, a property that is utilized in single molecule spectroscopy to prove the isolation of a single quantum emitter [1

1. F. Treussart, A. Clouqueur, C. Grossman, and J.-F. Roch, “Photon antibunching in the fluorescence of a single dye molecule embedded in a thin polymer film,” Opt. Lett. 26(19), 1504–1506 (2001). [CrossRef] [PubMed]

13

13. G. Nair, J. Zhao, and M. G. Bawendi, “Biexciton quantum yield of single semiconductor nanocrystals from photon statistics,” Nano Lett. 11(3), 1136–1140 (2011). [CrossRef] [PubMed]

]. In fact, the area ratio between center peak and lateral or side peaks, R, has been used to determine the number of m identical emitters under illumination: R = (m-1)/m [10

10. W. Becker, Advanced Time-Correlated Single Photon Counting Techniques Chemical Physics (Springer, 2005).

12

12. K. D. Weston, M. Dyck, P. Tinnefeld, C. Müller, D. P. Herten, and M. Sauer, “Measuring the number of independent emitters in single-molecule fluorescence images and trajectories using coincident photons,” Anal. Chem. 74(20), 5342–5349 (2002). [CrossRef] [PubMed]

].

In some emitters, such as quantum dots, optical generation of multi-excitons can lead to the emission of multiple photons in a single excitation cycle via a quantum cascade process [14

14. E. Moreau, I. Robert, L. Manin, V. Thierry-Mieg, J. M. Gérard, and I. Abram, “Quantum cascade of photons in semiconductor quantum dots,” Phys. Rev. Lett. 87(18), 183601 (2001). [CrossRef]

16

16. B. Fisher, J. M. Caruge, D. Zehnder, and M. Bawendi, “Room-temperature ordered photon emission from multiexciton states in single CdSe core-shell nanocrystals,” Phys. Rev. Lett. 94(8), 087403 (2005). [CrossRef] [PubMed]

]. When the emission of these multi-excitons are not spectrally excluded in a g(2) measurement, they contribute to the zero time delay peak. Thus, it has been shown that for a single, well isolated, quantum dot in the low pump intensity limit, R is directly proportional to the ratio between the bi-exciton quantum yield, QBX, and single exciton quantum yield, QX i.e. R = QBX/QX [13

13. G. Nair, J. Zhao, and M. G. Bawendi, “Biexciton quantum yield of single semiconductor nanocrystals from photon statistics,” Nano Lett. 11(3), 1136–1140 (2011). [CrossRef] [PubMed]

,17

17. Y. S. Park, A. V. Malko, J. Vela, Y. Chen, Y. Ghosh, F. García-Santamaría, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Near-unity quantum yields of biexciton emission from CdSe/CdS nanocrystals measured using single-particle spectroscopy,” Phys. Rev. Lett. 106(18), 187401 (2011). [CrossRef] [PubMed]

].

Recently, much effort has been devoted to the study of nanocrystal quantum dots (NQDs) with large bi-exciton quantum yields [17

17. Y. S. Park, A. V. Malko, J. Vela, Y. Chen, Y. Ghosh, F. García-Santamaría, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Near-unity quantum yields of biexciton emission from CdSe/CdS nanocrystals measured using single-particle spectroscopy,” Phys. Rev. Lett. 106(18), 187401 (2011). [CrossRef] [PubMed]

19

19. R. Osovsky, D. Cheskis, V. Kloper, A. Sashchiuk, M. Kroner, and E. Lifshitz, “Continuous-wave pumping of multiexciton bands in the photoluminescence spectrum of a single CdTe-CdSe core-shell colloidal quantum dot,” Phys. Rev. Lett. 102(19), 197401 (2009). [CrossRef] [PubMed]

]. NQDs with high bi-exciton quantum yield are important for light amplification [20

20. V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollingsworth, C. A. Leatherdale, H.-J. Eisler, and M. G. Bawendi, “Optical gain and stimulated emission in nanocrystal quantum dots,” Science 290(5490), 314–317 (2000). [CrossRef] [PubMed]

], multi-exciton generation [21

21. A. Shabaev, A. L. Efros, and A. J. Nozik, “Multiexciton generation by a single photon in nanocrystals,” Nano Lett. 6(12), 2856–2863 (2006). [CrossRef] [PubMed]

,22

22. R. D. Schaller and V. I. Klimov, “High efficiency carrier multiplication in PbSe nanocrystals: Implications for solar energy conversion,” Phys. Rev. Lett. 92(18), 186601 (2004). [CrossRef] [PubMed]

], and photon pair source applications [23

23. A. Muller, W. Fang, J. Lawall, and G. S. Solomon, “Creating polarization-entangled photon pairs from a semiconductor quantum dot using the optical Stark effect,” Phys. Rev. Lett. 103(21), 217402 (2009). [CrossRef] [PubMed]

,24

24. R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper, D. A. Ritchie, and A. J. Shields, “A semiconductor source of triggered entangled photon pairs,” Nature 439(7073), 179–182 (2006). [CrossRef] [PubMed]

]. As QBX plays a critical role in understanding the relationship between NQD PL blinking [25

25. M. Nirmal, B. O. Dabbousi, M. G. Bawendi, J. J. Macklin, J. K. Trautman, T. D. Harris, and L. E. Brus, “Fluorescence intermittency in single cadmium selenide nanocrystals,” Nature 383(6603), 802–804 (1996). [CrossRef]

,26

26. M. Kuno, D. P. Fromm, H. F. Hamann, A. Gallagher, and D. J. Nesbitt, “Nonexponential “blinking” kinetics of single CdSe quantum dots: A universal power law behavior,” J. Chem. Phys. 112(7), 3117–3120 (2000). [CrossRef]

] and the suppression of Auger recombination, determining QBX is an important part of this puzzle [17

17. Y. S. Park, A. V. Malko, J. Vela, Y. Chen, Y. Ghosh, F. García-Santamaría, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Near-unity quantum yields of biexciton emission from CdSe/CdS nanocrystals measured using single-particle spectroscopy,” Phys. Rev. Lett. 106(18), 187401 (2011). [CrossRef] [PubMed]

,18

18. Y. Louyer, L. Biadala, J. B. Trebbia, M. J. Fernée, P. Tamarat, and B. Lounis, “Efficient biexciton emission in elongated CdSe/ZnS nanocrystals,” Nano Lett. 11(10), 4370–4375 (2011). [CrossRef] [PubMed]

,27

27. C. Galland, Y. Ghosh, A. Steinbrück, M. Sykora, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots,” Nature 479(7372), 203–207 (2011). [CrossRef] [PubMed]

29

29. J. Zhao, G. Nair, B. R. Fisher, and M. G. Bawendi, “Challenge to the charging model of semiconductor-nanocrystal fluorescence intermittency from off-state quantum yields and multiexciton blinking,” Phys. Rev. Lett. 104(15), 157403 (2010). [CrossRef] [PubMed]

].

Importantly, g(2) based QBX measurements hinge upon the complete isolation of individual NQDs. However, when the combined effects of both clustering and multi-exciton emission are considered together, the ratio R can be expressed as:

R=(m1)QX+QBXmQX.
(1)

Here we assume that all m NQDs are identical: having equal excitation probabilities and identical QX and QBX values. Therefore, when measuring large QBX values, or rather, R > 0.5, an independent measure of NQD isolation becomes necessary [30

30. Y. Chen, J. Vela, H. Htoon, J. L. Casson, D. J. Werder, D. A. Bussian, V. I. Klimov, and J. A. Hollingsworth, ““Giant” multishell CdSe nanocrystal quantum dots with suppressed blinking,” J. Am. Chem. Soc. 130(15), 5026–5027 (2008). [CrossRef] [PubMed]

]. Independent verification of NQD isolation might include high-resolution techniques such as AFM, SEM, or TEM. However, such techniques have limited utility in that they require additional specialized instrumentation, they are time consuming, and it is difficult to perform these high resolution microscopies and single dot spectroscopy on the same set of NQDs. Most importantly, these techniques are not appropriate for many types of samples such as NQDs embedded in polymer films or biological tissues. In this regard, an all-optical approach capable of disentangling the contributions of clustering and multi-exciton emission is essential to interpret g(2) measurements without ambiguity.

We now demonstrate that the application of an appropriate time gate to a g(2) measurement allows for the separation of various factors contributing to R. Specifically, this technique allows for the determination of the extent of clustering (m), as well as the QBX/QX ratio. Furthermore, by conducting a detailed analysis on the decay functionality of R with respect to the gate delay time (GDT), we determine general conditions required for effective utilization of this approach. Analyzing this decay functionality also yields a method for determining lifetimes of bi-exciton states (τBX). Existing approaches for measuring τBX involve fitting PL decays measured as a function of pump power with multi-exponential functions [31

31. V. I. Klimov, A. A. Mikhailovsky, D. W. McBranch, C. A. Leatherdale, and M. G. Bawendi, “Quantization of multiparticle Auger rates in semiconductor quantum dots,” Science 287(5455), 1011–1013 (2000). [CrossRef] [PubMed]

,32

32. F. García-Santamaría, Y. Chen, J. Vela, R. D. Schaller, J. A. Hollingsworth, and V. I. Klimov, “Suppressed Auger recombination in “giant” nanocrystals boosts optical gain performance,” Nano Lett. 9(10), 3482–3488 (2009). [CrossRef] [PubMed]

]. In contrast, our approach requires fewer fitting parameters, and more importantly, allows for the determination of τBX at low pump powers, where contributions from higher order multi-excitons are minimal. In this regard, this approach could serve as a valuable tool in investigating technologically important multi-exciton processes in NQDs, such as optical amplification and multiple exciton generation.

2. Time-gating principle

Our approach exploits the fact that the bi-exciton emission always precedes single exciton emission. We selectively detect the photon emissions of the single excitons through the use of a time gate (only photons arriving within the gate time are analyzed) where the beginning of the gate (the gate delay time – GDT) is set to be much longer than the lifetime of bi-excitons. The g(2) function constructed out of these photons will be essentially void of all bi-exciton contributions, yielding the only the degree of clustering, with the familiar form of R:

limGDTRTG=(m1)m.
(2)

We use the subscript TG to denote that time-gating has been applied. With the ability to remove all bi-exciton contributions, we are able to determine if a NQD is in fact well isolated without ambiguity, even if it has a large bi-exciton quantum yield. Furthermore, we can apply the degree of clustering, m, found by Eq. (2) into Eq. (1) to obtain the average QBX of the NQDs in the cluster as: QBX=(RRTG)/(1RTG).

Time-gating is a feature available on many Single Photon Avalanche Photodiodes (SPADs) where a digital input signal enables photon detection for a given time window (Fig. 1
Fig. 1 Schematic of TCSPC implementations. (a) TCSPC setup allowing for hardware-implemented time-gating. (b) TCSPC setup allowing for software-implemented time-gating. (c) Details of TCSPC calculations. Photon arrival times are indicated by red circles while laser pulses are denoted by blue stars. PL lifetimes are determined by histogramming t values. Time-gating is implemented by using only photons arriving within the time-gated region, depicted by the yellow boxes. The gate-delay time (GDT) is also indicated. Anti-bunching plots are built up by histogramming the time differences, ΔT, between photons arriving on opposing channels.
). Thus, a hardware based time-gating approach is well-suited for a measurement where the goal is to identify single emitters. While this hardware implementation is simple, it requires a separate photon correlation experiment to acquire g(2) at different GDT values. Since such experiments are time consuming it becomes impossible to study RTG as a function GDT, a study required to validate this approach. For this reason, here we utilize a software-based time correlated single photon counting (TCSPC) approach. Specifically, we record the photon arrival times originating from multiple detectors with respect to both the start of the experiment (macro-time) and to a common excitation sync pulse (micro-time) as depicted in Fig. 1(c). This allows for the simultaneous collection of both the PL decay dynamics and g(2) function. Importantly, this approach allows for selective analysis of only photons that arrive after a certain time delay following the sync pulse, which enables the construction of a time gated g(2) function for any arbitrary GDT value.

3. Results and discussion

We applied this software-based time-gating approach to CdSe/CdS core thick shell NQDs (a.k.a giant NQDs), which exhibit nonblinking PL with minimal residual intensity flickering [17

17. Y. S. Park, A. V. Malko, J. Vela, Y. Chen, Y. Ghosh, F. García-Santamaría, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Near-unity quantum yields of biexciton emission from CdSe/CdS nanocrystals measured using single-particle spectroscopy,” Phys. Rev. Lett. 106(18), 187401 (2011). [CrossRef] [PubMed]

,27

27. C. Galland, Y. Ghosh, A. Steinbrück, M. Sykora, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots,” Nature 479(7372), 203–207 (2011). [CrossRef] [PubMed]

,30

30. Y. Chen, J. Vela, H. Htoon, J. L. Casson, D. J. Werder, D. A. Bussian, V. I. Klimov, and J. A. Hollingsworth, ““Giant” multishell CdSe nanocrystal quantum dots with suppressed blinking,” J. Am. Chem. Soc. 130(15), 5026–5027 (2008). [CrossRef] [PubMed]

,33

33. D. Canneson, I. Mallek-Zouari, S. Buil, X. Quelin, C. Javaux, B. Dubertret, and J.-P. Hermier, “Enhancing the fluorescence of individual thick shell CdSe/CdS Nanocrystals by coupling to gold structures,” New J. Phys. 14(6), 063035 (2012). [CrossRef]

]. In Fig. 2
Fig. 2 Single NQD data. Panels (a)-(d) and (e)-(h) correspond to different measurements/data sets. (a) PL lifetime from a single detector channel. Dash line: single exponential fit with time constant of 124 ns. (b) Standard g(2) plot before time-gating. R = 0.50 (c) Plot of RTG vs. GDT. Notice that the first 25 ns (before t = 0) are flat, this corresponds to the time before the sync pulse, due to the electronic delay in the system as is also seen in all lifetime plots. (d) g(2) plot after time gating has been applied (GDT = 75 ns, RTG(75) = 0.05). Note that most if this is due to cross-talk (sharp central spikes). (e) PL lifetime from a single detector channel. Dash line: double exponential fit with time constant of 23.7 and 110.5 ns. (f) Standard g(2) plot before time-gating. R = 0.73 (g) Plot of RTG as a function of GDT. (h) g(2) plot after time gating has been applied (GDT = 75 ns, RTG(7 5) = 0.13).
, we display the PL decay dynamics, g(2) before the time gating, decay of RTG as the function of GDT, and g(2) after application of GDTs for two different giant-NQDs (g-NQDs). While the observation that R is > 0.5 in both g-NQDs suggests that these g-NQDs have very high QBX, this measurement alone cannot rule out the possibility of NQD clusters. However, the decay of RTG towards zero with the increase of GDT (Figs. 2(c) and 2(g)) and observation of near complete photon anti-bunching after time gating at 75 ns (Figs. 2(d) and 2(h)) provide clear evidence that these two NQDs are well isolated and R values in each case indeed provide a direct measure of the QBX.

However, RTG values do not decay completely to zero as they should for single quantum emitters (cf. Figures 2(d) and 2(h)). Our analysis revealed that this residual value originates mainly from the sharp spike at zero time delay, which is composed of two peaks separated to one another by a time delay of ~30 ns. This doublet is the characteristic feature of cross-talk between the two SPADs of our HBT spectrometer. In general, several other factors such as the presence of dark-counts, background noise, and a pulse period that does not allow for complete NQD relaxation can also contribute to this residual value. The total contribution of these experimental artifacts together [10

10. W. Becker, Advanced Time-Correlated Single Photon Counting Techniques Chemical Physics (Springer, 2005).

13

13. G. Nair, J. Zhao, and M. G. Bawendi, “Biexciton quantum yield of single semiconductor nanocrystals from photon statistics,” Nano Lett. 11(3), 1136–1140 (2011). [CrossRef] [PubMed]

] can add error in the range of 2%-10% in determination of center peak area in our measurement.

Additionally, our analysis of the decay of RTG provides another powerful way to extract the recombination time of bi-excitons. By substituting the value of τX and α attained from Figs. 2(a) and 2(c) in Eq. (5), we determine τBX = 13.4 ns. While this τBX value is extracted without requiring any assumptions, it is close to a 14.0 ns lifetime that can be calculated from τX = 112 ns and QBX = 0.5, assuming the statistical scaling of ΓRad,BX. The τBX value extracted for the second g-NQDs (Figs. 2(e)-(h) also exhibits a similar agreement: τBX = 22.9 ns as calculated using Eq. (5), vs. τBX = 28.5 ns as calculated from a statistical scaling model (τX = 156 ns and QBX = 0.73). Our time-gating experiment is performed at low pump power (i.e., the average exciton population per pulse (μ) is below 0.1). The nearly single exponential decay shown in Fig. 2(a) indicates that bi-exciton emission is minimal, yet we can extract τBX via RTG versus GDT data. In this way, our time-gated g(2) approach presents a better and more accurate measurement of τBX in single-particle studies, as this extracted τBX value is free of contributions from higher order multi-excitons [34

34. Due to very high QBX, then second g-NQD shows a bi-exponential decay even at very low pump power. The fast time constant of the PL decay 23.78 ns is in good agreement with 22.9ns τBX extracted from the decay of RTG.”

].

Thus far, we have considered isolated NQDs and demonstrated the power of our approach in rejecting multi-excitonic contributions to g(2) measurements. However, the significance of our approach becomes even more evident when it is applied to a cluster of NQDs. In this case, our approach not only allows the extraction of the average QBX and τBX of NQDs in the cluster, it also provides some insight to the nature of clustering. Figure 3
Fig. 3 Single NQD data. (a) PL lifetime from a single detector channel. (b) Standard g(2) plot, no time gating (R = 0.73). (c) Plot of RTG vs. GDT. (d) g(2) plot after time gating has been applied (GDT = 75 ns, RTG(75) = 0.28).
provides a clear demonstration of this point.

The conventional g(2) measurement shown in Fig. 3(b) yields an R value of 0.73. While this value decays exponentially with GDT, the decay asymptotically approaches a value of 0.28. This provides clear evidence of clustering. A simple substitution of RTG and R to Eq. (1) and Eq. (2) gives a value of m = 1.39 NQDs with an average QBX value of 0.63. Furthermore, by including the effects of clustering in the analysis for the decay of the RTG, we extract the average τBX to be 6.2 ns.

Since a cluster of two identical dots will yield an RTG value approaching 0.5, the value found here of RTG = 0.28 (and thus m = 1.39) provides a clear indication that two (or more) non-identical dots are being examined. The cluster in this study could be composed of NQDs with unequal QX and/or unequal excitation probability. Specifically, for a cluster of 2 NQDs with equal excitation probability it can be shown that a difference in their QX value with a ratio of 1:0.2 can give rise to the RTG of 0.28. On the other hand, for 2 NQDs with identical QX, a difference in excitation probability with the same ratio is necessary. The excitation probability difference can arise from a scenario in which 2 identical NQDs are separated by some distance and are excited by laser spot with Gaussian intensity distribution.

4. Summary

In summary, we have demonstrated a new method to successfully discriminate between clusters of similar particles and well isolated single emitters with a high bi-exciton quantum yield. Notably, this method has added utility by providing a means for estimating the size of a cluster, even if it contains particles having high QBX values, without the need for spectral rejection of multi-excitonic spectral lines. It can also be used as a powerful tool to determine the bi-exciton lifetime of a single particle with much less influence from higher order multi-excitons. Recently a post photon selection approach, in which first and second photon detection events in a g(2) experiment are separated to extract the decay of BX is reported by Canneson et al. [33

33. D. Canneson, I. Mallek-Zouari, S. Buil, X. Quelin, C. Javaux, B. Dubertret, and J.-P. Hermier, “Enhancing the fluorescence of individual thick shell CdSe/CdS Nanocrystals by coupling to gold structures,” New J. Phys. 14(6), 063035 (2012). [CrossRef]

]. Although this approach can be considered as a more direct approach to extract BX decay, it is incapable of disentangling the contribution of multi-exciton emission and clustering in a g(2) experiment. Furthermore, in the case of a NQD exhibiting PL intensity fluctuations, our approach can be extended to extract QBX, τBX and the degree of clustering for different emissive levels of g-NQDs that are often associated with different charge exciton states [27

27. C. Galland, Y. Ghosh, A. Steinbrück, M. Sykora, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots,” Nature 479(7372), 203–207 (2011). [CrossRef] [PubMed]

]. Additionally, while we have focused on colloidal quantum dot samples in this letter, this technique should be widely applicable to virtually any type of sample where single-particle analysis is relevant.

5. Methods

5.1 Data collection

Quantum dots with 5.5 nm CdSe cores having nominally 15 monolayers of CdS grown using a SILAR method [35

35. Y. Ghosh, B. D. Mangum, J. L. Casson, D. J. Williams, H. Htoon, and J. A. Hollingsworth, “New insights into the complexities of shell growth and the strong influence of particle volume in nonblinking “giant” core/shell nanocrystal quantum dots,” J. Am. Chem. Soc. 134(23), 9634–9643 (2012). [CrossRef] [PubMed]

] were drop cast onto glass coverslips. Pulsed laser excitation (405 nm, 70 ps pulse-width) was used to elicit PL (centered at 650 nm) from the NQDs, which was detected by a pair of SPADs (Perkin Elmer, SPCM-AQR14) in a custom setup with a HBT detection scheme as described above. Photon arrivals were recorded with a HydraHarp 400 TCSPC module (PicoQuant). A 532 nm long pass filter was used to reject laser scatter and a 775 nm short pass filter was placed in front of each detector to minimize cross-talk. The laser power was reduced to ~200 pW and focused to a near diffraction limited spot (NA 1.3, 100x). Values for μ are estimated to be μ ~0.1.

5.2 Data analysis

Time-gating was applied by removing all photons from the data stream having micro-time (t) values less than GDT as depicted in Fig. 1. Subsequently, g(2) plots were created in the same fashion as is done without time gating: a histogram of time differences is created for photons arriving on different channels as depicted in Fig. 1(c).

Acknowledgments

This work was conducted at the Center for Integrated Nanotechnologies (CINT), a U.S. Department of Energy (DOE), Office of Science (OS), Office of Basic Energy Sciences (OBES) user facility and nanoscale science research center. B.D.M and H.H. acknowledge a Single-Investigator Small-Group Research Award (2009LANL1096), OBES, OS, U.S. DOE. Y.G. is supported by Los Alamos National Laboratory Directed Research and Development Funds. J.A.H. acknowledges NIH-NIGMS Grant 1R01GM084702-01.

References and links

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P. Michler, A. Kiraz, C. Becher, W. V. Schoenfeld, P. M. Petroff, L. Zhang, E. Hu, and A. Imamoglu, “A quantum dot single-photon turnstile device,” Science 290(5500), 2282–2285 (2000). [CrossRef] [PubMed]

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P. Michler, A. Imamoglu, M. D. Mason, P. J. Carson, G. F. Strouse, and S. K. Buratto, “Quantum correlation among photons from a single quantum dot at room temperature,” Nature 406(6799), 968–970 (2000). [CrossRef] [PubMed]

6.

A. Högele, C. Galland, M. Winger, and A. Imamoğlu, “Photon antibunching in the photoluminescence spectra of a single carbon nanotube,” Phys. Rev. Lett. 100(21), 217401 (2008). [CrossRef] [PubMed]

7.

C. Kurtsiefer, S. Mayer, P. Zarda, and H. Weinfurter, “Stable solid-state source of single photons,” Phys. Rev. Lett. 85(2), 290–293 (2000). [CrossRef] [PubMed]

8.

A. Beveratos, R. Brouri, T. Gacoin, J.-P. Poizat, and P. Grangier, “Nonclassical radiation from diamond nanocrystals,” Phys. Rev. A 64(6), 061802 (2001). [CrossRef]

9.

R. Brouri, A. Beveratos, J.-P. Poizat, and P. Grangier, “Photon antibunching in the fluorescence of individual color centers in diamond,” Opt. Lett. 25(17), 1294–1296 (2000). [CrossRef] [PubMed]

10.

W. Becker, Advanced Time-Correlated Single Photon Counting Techniques Chemical Physics (Springer, 2005).

11.

P. Tinnefeld, C. Müller, and M. Sauer, “Time-varying photon probability distribution of individual molecules at room temperature,” Chem. Phys. Lett. 345(3-4), 252–258 (2001). [CrossRef]

12.

K. D. Weston, M. Dyck, P. Tinnefeld, C. Müller, D. P. Herten, and M. Sauer, “Measuring the number of independent emitters in single-molecule fluorescence images and trajectories using coincident photons,” Anal. Chem. 74(20), 5342–5349 (2002). [CrossRef] [PubMed]

13.

G. Nair, J. Zhao, and M. G. Bawendi, “Biexciton quantum yield of single semiconductor nanocrystals from photon statistics,” Nano Lett. 11(3), 1136–1140 (2011). [CrossRef] [PubMed]

14.

E. Moreau, I. Robert, L. Manin, V. Thierry-Mieg, J. M. Gérard, and I. Abram, “Quantum cascade of photons in semiconductor quantum dots,” Phys. Rev. Lett. 87(18), 183601 (2001). [CrossRef]

15.

E. Dekel, D. V. Regelman, D. Gershoni, E. Ehrenfreund, W. V. Schoenfeld, and P. M. Petroff, “Cascade evolution and radiative recombination of quantum dot multiexcitons studied by time-resolved spectroscopy,” Phys. Rev. B 62(16), 11038–11045 (2000). [CrossRef]

16.

B. Fisher, J. M. Caruge, D. Zehnder, and M. Bawendi, “Room-temperature ordered photon emission from multiexciton states in single CdSe core-shell nanocrystals,” Phys. Rev. Lett. 94(8), 087403 (2005). [CrossRef] [PubMed]

17.

Y. S. Park, A. V. Malko, J. Vela, Y. Chen, Y. Ghosh, F. García-Santamaría, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Near-unity quantum yields of biexciton emission from CdSe/CdS nanocrystals measured using single-particle spectroscopy,” Phys. Rev. Lett. 106(18), 187401 (2011). [CrossRef] [PubMed]

18.

Y. Louyer, L. Biadala, J. B. Trebbia, M. J. Fernée, P. Tamarat, and B. Lounis, “Efficient biexciton emission in elongated CdSe/ZnS nanocrystals,” Nano Lett. 11(10), 4370–4375 (2011). [CrossRef] [PubMed]

19.

R. Osovsky, D. Cheskis, V. Kloper, A. Sashchiuk, M. Kroner, and E. Lifshitz, “Continuous-wave pumping of multiexciton bands in the photoluminescence spectrum of a single CdTe-CdSe core-shell colloidal quantum dot,” Phys. Rev. Lett. 102(19), 197401 (2009). [CrossRef] [PubMed]

20.

V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollingsworth, C. A. Leatherdale, H.-J. Eisler, and M. G. Bawendi, “Optical gain and stimulated emission in nanocrystal quantum dots,” Science 290(5490), 314–317 (2000). [CrossRef] [PubMed]

21.

A. Shabaev, A. L. Efros, and A. J. Nozik, “Multiexciton generation by a single photon in nanocrystals,” Nano Lett. 6(12), 2856–2863 (2006). [CrossRef] [PubMed]

22.

R. D. Schaller and V. I. Klimov, “High efficiency carrier multiplication in PbSe nanocrystals: Implications for solar energy conversion,” Phys. Rev. Lett. 92(18), 186601 (2004). [CrossRef] [PubMed]

23.

A. Muller, W. Fang, J. Lawall, and G. S. Solomon, “Creating polarization-entangled photon pairs from a semiconductor quantum dot using the optical Stark effect,” Phys. Rev. Lett. 103(21), 217402 (2009). [CrossRef] [PubMed]

24.

R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper, D. A. Ritchie, and A. J. Shields, “A semiconductor source of triggered entangled photon pairs,” Nature 439(7073), 179–182 (2006). [CrossRef] [PubMed]

25.

M. Nirmal, B. O. Dabbousi, M. G. Bawendi, J. J. Macklin, J. K. Trautman, T. D. Harris, and L. E. Brus, “Fluorescence intermittency in single cadmium selenide nanocrystals,” Nature 383(6603), 802–804 (1996). [CrossRef]

26.

M. Kuno, D. P. Fromm, H. F. Hamann, A. Gallagher, and D. J. Nesbitt, “Nonexponential “blinking” kinetics of single CdSe quantum dots: A universal power law behavior,” J. Chem. Phys. 112(7), 3117–3120 (2000). [CrossRef]

27.

C. Galland, Y. Ghosh, A. Steinbrück, M. Sykora, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots,” Nature 479(7372), 203–207 (2011). [CrossRef] [PubMed]

28.

S. Jander, A. Kornowski, and H. Weller, “Energy transfer from CdSe/CdS nanorods to amorphous carbon,” Nano Lett. 11(12), 5179–5183 (2011). [CrossRef] [PubMed]

29.

J. Zhao, G. Nair, B. R. Fisher, and M. G. Bawendi, “Challenge to the charging model of semiconductor-nanocrystal fluorescence intermittency from off-state quantum yields and multiexciton blinking,” Phys. Rev. Lett. 104(15), 157403 (2010). [CrossRef] [PubMed]

30.

Y. Chen, J. Vela, H. Htoon, J. L. Casson, D. J. Werder, D. A. Bussian, V. I. Klimov, and J. A. Hollingsworth, ““Giant” multishell CdSe nanocrystal quantum dots with suppressed blinking,” J. Am. Chem. Soc. 130(15), 5026–5027 (2008). [CrossRef] [PubMed]

31.

V. I. Klimov, A. A. Mikhailovsky, D. W. McBranch, C. A. Leatherdale, and M. G. Bawendi, “Quantization of multiparticle Auger rates in semiconductor quantum dots,” Science 287(5455), 1011–1013 (2000). [CrossRef] [PubMed]

32.

F. García-Santamaría, Y. Chen, J. Vela, R. D. Schaller, J. A. Hollingsworth, and V. I. Klimov, “Suppressed Auger recombination in “giant” nanocrystals boosts optical gain performance,” Nano Lett. 9(10), 3482–3488 (2009). [CrossRef] [PubMed]

33.

D. Canneson, I. Mallek-Zouari, S. Buil, X. Quelin, C. Javaux, B. Dubertret, and J.-P. Hermier, “Enhancing the fluorescence of individual thick shell CdSe/CdS Nanocrystals by coupling to gold structures,” New J. Phys. 14(6), 063035 (2012). [CrossRef]

34.

Due to very high QBX, then second g-NQD shows a bi-exponential decay even at very low pump power. The fast time constant of the PL decay 23.78 ns is in good agreement with 22.9ns τBX extracted from the decay of RTG.”

35.

Y. Ghosh, B. D. Mangum, J. L. Casson, D. J. Williams, H. Htoon, and J. A. Hollingsworth, “New insights into the complexities of shell growth and the strong influence of particle volume in nonblinking “giant” core/shell nanocrystal quantum dots,” J. Am. Chem. Soc. 134(23), 9634–9643 (2012). [CrossRef] [PubMed]

OCIS Codes
(300.0300) Spectroscopy : Spectroscopy
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6500) Spectroscopy : Spectroscopy, time-resolved

ToC Category:
Spectroscopy

History
Original Manuscript: December 21, 2012
Revised Manuscript: March 3, 2013
Manuscript Accepted: March 8, 2013
Published: March 18, 2013

Citation
Benjamin D. Mangum, Yagnaseni Ghosh, Jennifer A. Hollingsworth, and Han Htoon, "Disentangling the effects of clustering and multi-exciton emission in second-order photon correlation experiments," Opt. Express 21, 7419-7426 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-6-7419


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References

  1. F. Treussart, A. Clouqueur, C. Grossman, and J.-F. Roch, “Photon antibunching in the fluorescence of a single dye molecule embedded in a thin polymer film,” Opt. Lett.26(19), 1504–1506 (2001). [CrossRef] [PubMed]
  2. T. Basché, W. E. Moerner, M. Orrit, and H. Talon, “Photon antibunching in the fluorescence of a single dye molecule trapped in a solid,” Phys. Rev. Lett.69(10), 1516–1519 (1992). [CrossRef] [PubMed]
  3. B. Lounis and W. E. Moerner, “Single photons on demand from a single molecule at room temperature,” Nature407(6803), 491–493 (2000). [CrossRef] [PubMed]
  4. P. Michler, A. Kiraz, C. Becher, W. V. Schoenfeld, P. M. Petroff, L. Zhang, E. Hu, and A. Imamoglu, “A quantum dot single-photon turnstile device,” Science290(5500), 2282–2285 (2000). [CrossRef] [PubMed]
  5. P. Michler, A. Imamoglu, M. D. Mason, P. J. Carson, G. F. Strouse, and S. K. Buratto, “Quantum correlation among photons from a single quantum dot at room temperature,” Nature406(6799), 968–970 (2000). [CrossRef] [PubMed]
  6. A. Högele, C. Galland, M. Winger, and A. Imamoğlu, “Photon antibunching in the photoluminescence spectra of a single carbon nanotube,” Phys. Rev. Lett.100(21), 217401 (2008). [CrossRef] [PubMed]
  7. C. Kurtsiefer, S. Mayer, P. Zarda, and H. Weinfurter, “Stable solid-state source of single photons,” Phys. Rev. Lett.85(2), 290–293 (2000). [CrossRef] [PubMed]
  8. A. Beveratos, R. Brouri, T. Gacoin, J.-P. Poizat, and P. Grangier, “Nonclassical radiation from diamond nanocrystals,” Phys. Rev. A64(6), 061802 (2001). [CrossRef]
  9. R. Brouri, A. Beveratos, J.-P. Poizat, and P. Grangier, “Photon antibunching in the fluorescence of individual color centers in diamond,” Opt. Lett.25(17), 1294–1296 (2000). [CrossRef] [PubMed]
  10. W. Becker, Advanced Time-Correlated Single Photon Counting Techniques Chemical Physics (Springer, 2005).
  11. P. Tinnefeld, C. Müller, and M. Sauer, “Time-varying photon probability distribution of individual molecules at room temperature,” Chem. Phys. Lett.345(3-4), 252–258 (2001). [CrossRef]
  12. K. D. Weston, M. Dyck, P. Tinnefeld, C. Müller, D. P. Herten, and M. Sauer, “Measuring the number of independent emitters in single-molecule fluorescence images and trajectories using coincident photons,” Anal. Chem.74(20), 5342–5349 (2002). [CrossRef] [PubMed]
  13. G. Nair, J. Zhao, and M. G. Bawendi, “Biexciton quantum yield of single semiconductor nanocrystals from photon statistics,” Nano Lett.11(3), 1136–1140 (2011). [CrossRef] [PubMed]
  14. E. Moreau, I. Robert, L. Manin, V. Thierry-Mieg, J. M. Gérard, and I. Abram, “Quantum cascade of photons in semiconductor quantum dots,” Phys. Rev. Lett.87(18), 183601 (2001). [CrossRef]
  15. E. Dekel, D. V. Regelman, D. Gershoni, E. Ehrenfreund, W. V. Schoenfeld, and P. M. Petroff, “Cascade evolution and radiative recombination of quantum dot multiexcitons studied by time-resolved spectroscopy,” Phys. Rev. B62(16), 11038–11045 (2000). [CrossRef]
  16. B. Fisher, J. M. Caruge, D. Zehnder, and M. Bawendi, “Room-temperature ordered photon emission from multiexciton states in single CdSe core-shell nanocrystals,” Phys. Rev. Lett.94(8), 087403 (2005). [CrossRef] [PubMed]
  17. Y. S. Park, A. V. Malko, J. Vela, Y. Chen, Y. Ghosh, F. García-Santamaría, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Near-unity quantum yields of biexciton emission from CdSe/CdS nanocrystals measured using single-particle spectroscopy,” Phys. Rev. Lett.106(18), 187401 (2011). [CrossRef] [PubMed]
  18. Y. Louyer, L. Biadala, J. B. Trebbia, M. J. Fernée, P. Tamarat, and B. Lounis, “Efficient biexciton emission in elongated CdSe/ZnS nanocrystals,” Nano Lett.11(10), 4370–4375 (2011). [CrossRef] [PubMed]
  19. R. Osovsky, D. Cheskis, V. Kloper, A. Sashchiuk, M. Kroner, and E. Lifshitz, “Continuous-wave pumping of multiexciton bands in the photoluminescence spectrum of a single CdTe-CdSe core-shell colloidal quantum dot,” Phys. Rev. Lett.102(19), 197401 (2009). [CrossRef] [PubMed]
  20. V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollingsworth, C. A. Leatherdale, H.-J. Eisler, and M. G. Bawendi, “Optical gain and stimulated emission in nanocrystal quantum dots,” Science290(5490), 314–317 (2000). [CrossRef] [PubMed]
  21. A. Shabaev, A. L. Efros, and A. J. Nozik, “Multiexciton generation by a single photon in nanocrystals,” Nano Lett.6(12), 2856–2863 (2006). [CrossRef] [PubMed]
  22. R. D. Schaller and V. I. Klimov, “High efficiency carrier multiplication in PbSe nanocrystals: Implications for solar energy conversion,” Phys. Rev. Lett.92(18), 186601 (2004). [CrossRef] [PubMed]
  23. A. Muller, W. Fang, J. Lawall, and G. S. Solomon, “Creating polarization-entangled photon pairs from a semiconductor quantum dot using the optical Stark effect,” Phys. Rev. Lett.103(21), 217402 (2009). [CrossRef] [PubMed]
  24. R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper, D. A. Ritchie, and A. J. Shields, “A semiconductor source of triggered entangled photon pairs,” Nature439(7073), 179–182 (2006). [CrossRef] [PubMed]
  25. M. Nirmal, B. O. Dabbousi, M. G. Bawendi, J. J. Macklin, J. K. Trautman, T. D. Harris, and L. E. Brus, “Fluorescence intermittency in single cadmium selenide nanocrystals,” Nature383(6603), 802–804 (1996). [CrossRef]
  26. M. Kuno, D. P. Fromm, H. F. Hamann, A. Gallagher, and D. J. Nesbitt, “Nonexponential “blinking” kinetics of single CdSe quantum dots: A universal power law behavior,” J. Chem. Phys.112(7), 3117–3120 (2000). [CrossRef]
  27. C. Galland, Y. Ghosh, A. Steinbrück, M. Sykora, J. A. Hollingsworth, V. I. Klimov, and H. Htoon, “Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots,” Nature479(7372), 203–207 (2011). [CrossRef] [PubMed]
  28. S. Jander, A. Kornowski, and H. Weller, “Energy transfer from CdSe/CdS nanorods to amorphous carbon,” Nano Lett.11(12), 5179–5183 (2011). [CrossRef] [PubMed]
  29. J. Zhao, G. Nair, B. R. Fisher, and M. G. Bawendi, “Challenge to the charging model of semiconductor-nanocrystal fluorescence intermittency from off-state quantum yields and multiexciton blinking,” Phys. Rev. Lett.104(15), 157403 (2010). [CrossRef] [PubMed]
  30. Y. Chen, J. Vela, H. Htoon, J. L. Casson, D. J. Werder, D. A. Bussian, V. I. Klimov, and J. A. Hollingsworth, ““Giant” multishell CdSe nanocrystal quantum dots with suppressed blinking,” J. Am. Chem. Soc.130(15), 5026–5027 (2008). [CrossRef] [PubMed]
  31. V. I. Klimov, A. A. Mikhailovsky, D. W. McBranch, C. A. Leatherdale, and M. G. Bawendi, “Quantization of multiparticle Auger rates in semiconductor quantum dots,” Science287(5455), 1011–1013 (2000). [CrossRef] [PubMed]
  32. F. García-Santamaría, Y. Chen, J. Vela, R. D. Schaller, J. A. Hollingsworth, and V. I. Klimov, “Suppressed Auger recombination in “giant” nanocrystals boosts optical gain performance,” Nano Lett.9(10), 3482–3488 (2009). [CrossRef] [PubMed]
  33. D. Canneson, I. Mallek-Zouari, S. Buil, X. Quelin, C. Javaux, B. Dubertret, and J.-P. Hermier, “Enhancing the fluorescence of individual thick shell CdSe/CdS Nanocrystals by coupling to gold structures,” New J. Phys.14(6), 063035 (2012). [CrossRef]
  34. Due to very high QBX, then second g-NQD shows a bi-exponential decay even at very low pump power. The fast time constant of the PL decay 23.78 ns is in good agreement with 22.9ns τBX extracted from the decay of RTG.”
  35. Y. Ghosh, B. D. Mangum, J. L. Casson, D. J. Williams, H. Htoon, and J. A. Hollingsworth, “New insights into the complexities of shell growth and the strong influence of particle volume in nonblinking “giant” core/shell nanocrystal quantum dots,” J. Am. Chem. Soc.134(23), 9634–9643 (2012). [CrossRef] [PubMed]

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