## Non-poissonian formation of multiple excitons in photoexcited CdTe colloidal quantum qots by femtosecond nonresonant two-photon absorption |

Optics Express, Vol. 21, Issue 20, pp. 24300-24308 (2013)

http://dx.doi.org/10.1364/OE.21.024300

Acrobat PDF (799 KB)

### Abstract

Using direct multiexcitonic spectroscopy, we experimentally observe for the first time the non-Poissonian formation of multiple excitons by femtosecond nonresonant two-photon absorption process in semiconductor colloidal quantum dots (QDs). Each of the multiple excitons is individually generated via the absorption of a pair of photons during the femtosecond pulse irradiation. The non-Poissonian distribution of the generated excitons is reflected as a non-quadratic dependence on the pulse intensity of the average number of excitons per QD. This is the main observation of the present work. It is explained by a multiexcitonic formation model that is based on the phenomenon of intrapulse state filling of the few quantum electronic states accessed by the two-photon transitions. The experiments are conducted with 3.9-nm CdTe QDs in room-temperature hexane solution using the femtosecond pump-probe transient absorption technique, where an intense pump pulse generates the excitons and a weak probe pulse measures their number via intraband one-photon absorption.

© 2013 OSA

## 1. Introduction

1. V. I. Klimov, *Nanocrystal Quantum Dots* (CRC, 2010). [CrossRef]

2. E. R. Thoen, E. M. Koontz, M. Joschko, P. Langlois, T. R. Schibli, F. X. Kartner, E. P. Ippen, and L. A. Kolodziejski, “Two-photon absorption in semiconductor saturable absorber mirrors,” Appl. Phys. Lett. **74**, 3927 (1999). [CrossRef]

17. Y. Qu, W. Ji, Y. Zheng, and J. Y. Ying, “Auger recombination and intraband absorption of two-photon-excited carriers in colloidal CdSe quantum dots,” Appl. Phys. Lett. **90**, 133112 (2007). [CrossRef]

2. E. R. Thoen, E. M. Koontz, M. Joschko, P. Langlois, T. R. Schibli, F. X. Kartner, E. P. Ippen, and L. A. Kolodziejski, “Two-photon absorption in semiconductor saturable absorber mirrors,” Appl. Phys. Lett. **74**, 3927 (1999). [CrossRef]

3. D. R. Larson, W. R. Zipfel, R. M. Williams, S. W. Clark, M. P. Bruchez, F. W. Wise, and W. W. Webb, “Water-Soluble Quantum Dots for Multiphoton Fluorescence Imaging in Vivo,” Science **300**, 1434 (2003). [CrossRef] [PubMed]

18. V. I. Klimov, “Spectral and Dynamical Properties of Multiexcitons in Semiconductor Nanocrystals,” Annu. Rev. Phys. Chem. **58**, 635 (2007). [CrossRef]

19. A. J. Nozik, “Multiple exciton generation in semiconductor quantum dots,” Chem. Phys. Lett. **457**, 3–11 (2009). [CrossRef]

## 2. Experiment

*-1S*

_{e}_{3/2,h}state) and 5% size distribution. CdTe QDs are chosen as the model system for the study due to the applicable band gap for their nonresonant two-photon absorption, excellent stability, good quantum yield, very simple crystal structure, and low degeneracy of the exciton states. The QDs are prepared according to the synthesis procedure given in [21

21. V. Kloper, R. Osovsky, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The growth of CdTe nanocrystals using in situ formed Cd0 crystalline particles,” J. Phys. Chem. C **111**, 10336 (2007). [CrossRef]

22. R. Osovsky, V. Kloper, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The Influience of small deviation from a spherical shape on the electronic and optical properties of CdTe nanocrystal quantum dots,” J. Phys. Chem. C **111**, 10841 (2007). [CrossRef]

21. V. Kloper, R. Osovsky, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The growth of CdTe nanocrystals using in situ formed Cd0 crystalline particles,” J. Phys. Chem. C **111**, 10336 (2007). [CrossRef]

22. R. Osovsky, V. Kloper, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The Influience of small deviation from a spherical shape on the electronic and optical properties of CdTe nanocrystal quantum dots,” J. Phys. Chem. C **111**, 10841 (2007). [CrossRef]

*ω*= 19 meV) and a central wavelength of 812 nm (photon energy of 1.53 eV). The pump pulse energy

_{FWHM}*E*ranges from 20

_{pump}*μ*J to 115

*μ*J corresponding in our experiment to peak pulse intensity

*I*

_{0,pump}of 108 GW/cm

^{2}to 620 GW/cm

^{2}, respectively. According to its intensity, the pulse generates multiple excitons within each QD via nonresonant two-photon absorption, with 〈

*N*

_{0}〉 as the corresponding average number of excitons per QD in the interaction region. To avoid heating, sample degradation, and multiple pulse effects, the pulse repetition rate is set to a low rate of 10 Hz and the QD sample is stirred during the experiments. The experimental values of 〈

*N*

_{0}〉 are obtained for a set of different pump pulse energies by the analysis of one-photon intraband transient absorption (intraTA) signals measured by a time-delayed weak near-infrared femtosecond probe pulse of 0.5

*μ*J energy. Except for the energy, the probe pulse is identical to the pump pulse. We have made sure that the probe pulse does not have sufficient intensity to excite the sample via two-photon absorption, so it can only induce intraband one-photon transitions within the conduction or valence bands following the pump pulse excitation. We attribute the present probe pulse absorption mostly to intraband hole excitation from the valence band-edge states, rather than to intraband electron excitation. This is in agreement with previous observations in similar systems [23

23. H. Zhu, N Song, W. Rodriguez-Cordoba, and T. Lian, “Wave Function Engineering for Efficient Extraction of up to Nineteen Electrons from One CdSe/CdS Quasi-Type II Quantum Dot,” J. Am. Chem. Soc. **134**, 4250–4257 (2012). [CrossRef] [PubMed]

## 3. Experimental and Theoretical-Model Results and Discussion

*α*(

*τ*), measured at a pump-probe delay time

*τ*is proportional to the average number of excitons per QD, 〈

*N*(

*τ*)〉, at the time of probing. Hence, 〈

*N*(

*τ*)〉 = Δ

*α*(

*τ*)/

*K*, with

_{sig_exc}*K*being the corresponding proportionality constant. This is true as long as our near-infrared one-photon intraband absorption cross-section per exciton is independent of the number of excitons residing in the QD. Since the one-photon intraband transition induced by the near-infrared probe pulse (photon energy of about 1.53 eV) excites the QD far above the band-edge into a region of very high density of hole states, this situation indeed holds in our case. Figure 1 presents several examples of the experimental results of 〈

_{sig_exc}*N*(

*τ*)〉 as a function of

*τ*, up to

*τ*=50 ps, for different pump pulse energies, together with the corresponding values obtained for 〈

*N*

_{0}〉. The results clearly show the increase in 〈

*N*

_{0}〉 with the increase in the pulse intensity, and the corresponding evolution from the single-excitonic [〈

*N*

_{0}〉=0.35 in Fig. 1(a)] to the multi-excitonic [〈

*N*

_{0}〉=3.80 in Fig. 1(f)] two-photon absorption regime.

*K*is obtained using the saturation behavior of the asymptotic probe signal, Δ

_{sig_exc}*α*=Δ

_{asymp}*α*(

*τ*=45–50ps), that occurs with the increase in pump pulse energy. As explained below, Δ

*α*is measured at pump-probe delays when each excited QD contains a single exciton, which is left after the cascaded decay of the multiple excitons initially generated in the QD. Thus, Δ

_{asymp}*α*is a measure of the total number of excited QDs that increases with the pump-pulse energy, until it reaches saturation when all the QDs in the interaction region are excited. At saturation, Δ

_{asymp}*α*corresponds to 〈

_{asymp_sat}*N*〉

*=1. Hence, one obtains that*

_{asymp}*K*=Δ

_{sig_exc}*α*and 〈

_{asym_sat}*N*(

*τ*)〉=Δ

*α*(

*τ*)/Δ

*α*. Such a saturation behavior of the asymptotic signal is indeed seen in our results of Fig. 1.

_{asymp_sat}*N*(

*τ*)〉 traces reflects a non-radiative cascaded mul-tiexcitonic decay of the generated excitons that proceeds as long as there is more than one exciton in the QD. In each step, for

*m*>1,

*m*excitons in the QD decay into

*m*−1 excitons. It is commonly interpreted to result from non-radiative Auger recombination of the charge carriers in the QD [24

24. 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**, 1011–1013 (2000). [CrossRef] [PubMed]

22. R. Osovsky, V. Kloper, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The Influience of small deviation from a spherical shape on the electronic and optical properties of CdTe nanocrystal quantum dots,” J. Phys. Chem. C **111**, 10841 (2007). [CrossRef]

*N*(

*τ*)〉 exhibit a multi-exponential picosecond decay behavior, where the decay constants of the various components correspond to the various lifetimes of multi-excitons of a different order m. By analyzing the total sum over all the 〈

*N*(

*τ*)〉 data, we have extracted the bi-excitonic (

*m*=2) and tri-excitonic (

*m*=3) lifetimes as

*τ*

_{2}=12.2±2 ps and

*τ*

_{3}=4.5±1.5 ps, respectively. For each trace, the value of 〈

*N*

_{0}〉 and its error are obtained by extrapolating the 〈

*N*(

*τ*)〉 results to time zero. It is done by averaging over the results obtained by numerically extrapolating the measured data up to 10 ps using 2nd-, 3rd-, and 4th-order polynomials.

*N*

_{0}〉 as a function of the pump pulse energy

*E*(circles) together with several analysis lines. One is a line of quadratic dependence on the pulse energy and intensity (black line) corresponding to

_{pump}*I*

_{0,pump}is the peak intensity of the pump pulse with energy

*E*. The presented line corresponds to

_{pump}^{4}/W

^{2}that, based on our experimental parameters, corresponds to the theoretical value of the single-excitonic two-photon absorption cross-section,

*N*

_{0}〉 results at the three lower pulse energies to a quadratic intensity dependence. As seen, the full set of experimental results of 〈

*N*

_{0}〉 significantly deviates from a quadratic dependence on

*I*

_{0,pump}and

*E*; the results fit this dependence only at the region of the lower 〈

_{pump}*N*

_{0}〉 values. As we explain, the meaning of this observed non-quadratic intensity dependence is the non-Poissonian formation of multiple excitons via nonresonant two-photon absorption.

*t*for an intrapulse exciton generation in a given QD via two-photon absorption is

*p*(

_{TPA}*t*) ∝

*s*(

_{TPA}*t*) × [

*I*(

_{pump}*t*)]

^{2}, where

*s*(

_{TPA}*t*) is the instantaneous effective two-photon absorption cross-section and

*I*(

_{pump}*t*) =

*g*(

*t*) ×

*I*

_{0,pump}is the instantaneous pump pulse intensity with

*g*(

*t*) as the pulse shape (here, 87-fs Gaussian). The total exciton generation probability is then obtained from integration over the full pulse as

*P*exhibits a quadratic dependence on

_{TPA}*I*

_{0,pump}only if

*s*(

_{TPA}*t*) is time-independent with a constant value along the entire pulse irradiation. This constant value is by definition equal to the two-photon absorption cross-section for generating the first exciton in the QD,

*σ*. When an ensemble of QDs is considered, since 〈

_{TPA}*N*

_{0}〉 ∝

*P*, the same conclusion also holds for the resulting values of 〈

_{TPA}*N*

_{0}〉. In the single-excitonic regime,

*s*(

_{TPA}*t*) =

*σ*always holds since no more than one exciton is generated in a QD, so the corresponding 〈

_{TPA}*N*

_{0}〉 values always exhibit a quadratic intensity dependence [4

4. K. I. Kang, B. P. McGinnis, Sandalphon, Y. Z. Hu, S. W. Koch, N. Peyghambarian, A. Mysyrowicz, L. C. Liu, and S. H. Risbud, “Confinement-induced valence-band mixing in CdS quantum dots observed by two-photon spectroscopy,” Phys. Rev. B **45**, 3465–3468 (1992). [CrossRef]

15. G. Xing, W. Ji, Y. Zheng, and J. Y. Ying, “Two- and three-photon absorption of semiconductor quantum dots in the vicinity of half of lowest exciton energy,” Appl. Phys. Lett. **93**, 241114 (2008). [CrossRef]

*s*(

_{TPA}*t*) =

*σ*and quadratic intensity dependence happens only if the generation of a new exciton is unaffected by the presence of other excitons in the QD i.e., it is effectively independent of the number of excitons already existing in the QD. Physically, such independence among different events of exciton generation in the same QD also implies that the multiple excitons generated by a given pulse in a QD’s ensemble follow the Poisson distribution, with

_{TPA}*m*excitons in a QD when 〈

*N*

_{0}〉 = ∑

*×*

_{m}m*P*(

_{Poisson}*m*) is the corresponding mean. Hence, the non-quadratic intensity dependence of 〈

*N*

_{0}〉 measured here reflects multiexcitonic formation by femtosecond nonresonant two-photon absorption with a distribution that significantly deviates from the Poisson distribution. This is the main observation of this research.

*N*

_{0}〉. The main ingredient of the model is the phenomenon of intrapulse state filling of the (few) electronic states corresponding to the excitonic states that are excited by the nonresonant two-photon transitions. The state filling effect, which originates from the Pauli exclusion principle, has previously been observed experimentally for QDs only in one-photon excitation processes (for example, see [18

18. V. I. Klimov, “Spectral and Dynamical Properties of Multiexcitons in Semiconductor Nanocrystals,” Annu. Rev. Phys. Chem. **58**, 635 (2007). [CrossRef]

1. V. I. Klimov, *Nanocrystal Quantum Dots* (CRC, 2010). [CrossRef]

*m*exciton in the QD is

^{th}*σ*is the single-excitonic two-photon absorption cross-section. Hence, for an ensemble of QDs, a given pulse generates a multiexcitonic distribution

_{TPA}*P*(

*m*) that is non-Poissonian [i.e.,

*P*(

*m*) ≠

*P*(

_{Poisson}*m*)] and its mean, 〈

*N*

_{0}〉 = ∑

*×*

_{m}m*P*(

*m*), is smaller than the mean of the equivalent Poissonian case, where the entire multiexcitonic formation occurs with a constant cross-section equal to

*σ*. The corresponding difference increases as the Poissonian value of 〈

_{TPA}*N*

_{0}〉 increases, or, equivalently, as the peak pulse intensity increases.

18. V. I. Klimov, “Spectral and Dynamical Properties of Multiexcitons in Semiconductor Nanocrystals,” Annu. Rev. Phys. Chem. **58**, 635 (2007). [CrossRef]

25. 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**, 197401 (2009). [CrossRef] [PubMed]

26. S. L. Sewall, R. R. Cooney, E. A. Dias, P. Tyagi, and P. Kambhampati, “State-resolved observation in real time of the structural dynamics of multiexcitons in semiconductor nanocrystals,” Phys. Rev. B **84**, 235304 (2011). [CrossRef]

*= −15 meV [25*

_{per_exc}25. 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**, 197401 (2009). [CrossRef] [PubMed]

26. S. L. Sewall, R. R. Cooney, E. A. Dias, P. Tyagi, and P. Kambhampati, “State-resolved observation in real time of the structural dynamics of multiexcitons in semiconductor nanocrystals,” Phys. Rev. B **84**, 235304 (2011). [CrossRef]

*m*− 1) excitons in the QD, i.e., for the generation of the

*m*exciton, all the two-photon transition energies are different by an amount of (

^{th}*m*− 1)×Δ

*from their values with zero excitons in the QD. As seen, the difference between the shifting and no-shifting cases is not significant for the deviation of our measured 〈*

_{per_exc}*N*

_{0}〉 values (circles) from the values of the Poissonian multiexcitonic formation (black line).

*–2P*

_{e}_{3/2,}

*, 1P*

_{h}_{1/2,e}– 2S

_{3/2,}

*and 1P*

_{h}_{3/2,e}–2S

_{3/2,h}having electronic degeneracy of

*DG*=2, 2 and 4, respectively. The state-specific information that depends on the QD diameter includes here the transition (excitation) energy and partial single-excitonic two-photon absorption cross-section (

*k*). Summing up all the partial cross-sections gives the total single-excitonic two-photon absorption cross-section

21. V. Kloper, R. Osovsky, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The growth of CdTe nanocrystals using in situ formed Cd0 crystalline particles,” J. Phys. Chem. C **111**, 10336 (2007). [CrossRef]

**111**, 10841 (2007). [CrossRef]

27. M. R. Salvador, M. A. Hines, and G. D. Scholes, “Exciton-bath coupling and inhomogeneous broadening in the optical spectroscopy of semiconductor quantum dots,” J. Chem. Phys. **118**, 9380–9388 (2003). [CrossRef]

*D*, which experiences a temporal pump pulse intensity

*I*(

_{pump}*t*), is numerically calculated over a time grid using the Monte Carlo method by following the time-dependent population of each of the electronic states corresponding to the different excitonic states accessed by the two-photon excitation. The probability

*p*(

_{k,TPA}*t*) of generating a new exciton at state

*k*at the time interval between

*t*and

*t*+

*dt*is determined by

*t*. Based on our model, it is given by

*DG*and

_{k}*k*. As defined above,

*k*. The factor

*T*originates from the multiexcitonic change in the transition energy of state

_{k}*k*that amounts to

*m*(

*t*) × Δ

*, where*

_{per_exc}*m*(

*t*) is the total number of excitons in the QD at time

*k*in the shifted-line case and unshifted-line case.

*I*(

_{pump}*t; r*) =

*I*

_{0,pump}(

*r*) ×

*g*(

*t*) where

*r*is the radial distance from the pump laser beam axis. After the pump pulse ending, the probed 〈

*N*

_{0}〉 value for this array is obtained by averaging over the final number of excitons in the different QDs of the array according to the spatial profile of the probe laser beam, i.e., the contribution from each QD is weighted by the relative intensity of the probe laser beam at the position of the QD. The final 〈

*N*

_{0}〉 value calculated for our experiment with a given pump pulse energy is obtained by applying a proper (weighted) averaging over the results calculated for several representative QD diameters within the size distribution of our sample. The model results in Fig. 2 present such calculated 〈

*N*

_{0}〉 values for different pump pulse energies. Their excellent quantitative agreement with the experimental results strongly supports the identification of the intrapulse electronic state filling as the key element behind the observed non-Poissonian multiexcitonic formation.

## 4. Conclusion

## Acknowledgments

## References and links

1. | V. I. Klimov, |

2. | E. R. Thoen, E. M. Koontz, M. Joschko, P. Langlois, T. R. Schibli, F. X. Kartner, E. P. Ippen, and L. A. Kolodziejski, “Two-photon absorption in semiconductor saturable absorber mirrors,” Appl. Phys. Lett. |

3. | D. R. Larson, W. R. Zipfel, R. M. Williams, S. W. Clark, M. P. Bruchez, F. W. Wise, and W. W. Webb, “Water-Soluble Quantum Dots for Multiphoton Fluorescence Imaging in Vivo,” Science |

4. | K. I. Kang, B. P. McGinnis, Sandalphon, Y. Z. Hu, S. W. Koch, N. Peyghambarian, A. Mysyrowicz, L. C. Liu, and S. H. Risbud, “Confinement-induced valence-band mixing in CdS quantum dots observed by two-photon spectroscopy,” Phys. Rev. B |

5. | R. Tommasi, M. Lepore, M. Ferrara, and I. M. Catalano, “Observation of high-index states in CdS |

6. | M. E. Schmidt, S. A. Blanton, M. A. Hines, and P. Guyot-Sionnest, “Size-dependent two-photon excitation spectroscopy of CdSe nanocrystals,” Phys. Rev. B |

7. | L. A. Padilha, J. Fu, D. J. Hagan, E. W. Van Stryland, C. L. Cesar, L. C. Barbosa, C. H. B. Cruz, D. Buso, and A. Martucci, “Frequency degenerate and nondegenerate two-photon absorption spectra of semiconductor quantum dots,” Phys. Rev. B |

8. | G. S. He, K. -T. Yong, Q. Zheng, Y. Sahoo, A. Baev, A. I. Ryasnyanskiy, and P. N. Prasad, “Multi-photon excitation properties of CdSe quantum dots solutions and optical limiting behavior in infrared range,” Opt. Express |

9. | S. -C. Pu, M. -J. Yang, C. -C. Hsu, C. -W. Lai, C. -C. Hsieh, S. H. Lin, Y. -M. Cheng, and P. -T. Chou, “The Empirical Correlation Between Size and Two-Photon Absorption Cross Section of CdSe and CdTe Quantum Dots.” Small |

10. | L. Pan, N. Tamai, K. Kamada, and S. Deki, “Nonlinear optical properties of thiol-capped CdTe quantum dots in nonresonant region,” Appl. Phys. Lett. |

11. | Y. Qu and W. Ji, “Two-photon absorption of quantum dots in the regime of very strong confinement: size and wavelength dependence,” J. Opt. Soc. Am. B |

12. | J. Khatei, C. S. Suchand Sandeep, R. Philip, and K. S. R. Koteswara Rao, “Near-resonant two-photon absorption in luminescent CdTe quantum dots,” Appl. Phys. Lett. |

13. | A. D. Lad, P. P. Kiran, D. More, G. Ravindra Kumar, and S. Mahamuni, “Two-photon absorption in ZnSe and ZnSe/ZnS core/shell quantum structures,” Appl. Phys. Lett. |

14. | S. A. Blanton, A. Dehestani, P. C. Lin, and P. Guyot-Sionnest, “Photoluminescence of single semiconductor nanocrystallites by two-photon excitation microscopy,” Chem. Phys. Lett. |

15. | G. Xing, W. Ji, Y. Zheng, and J. Y. Ying, “Two- and three-photon absorption of semiconductor quantum dots in the vicinity of half of lowest exciton energy,” Appl. Phys. Lett. |

16. | J. He, J. Mi, H. Li, and W. Ji, “Observation of Interband Two-Photon Absorption Saturation in CdS Nanocrystals,” J. Phys. Chem. B |

17. | Y. Qu, W. Ji, Y. Zheng, and J. Y. Ying, “Auger recombination and intraband absorption of two-photon-excited carriers in colloidal CdSe quantum dots,” Appl. Phys. Lett. |

18. | V. I. Klimov, “Spectral and Dynamical Properties of Multiexcitons in Semiconductor Nanocrystals,” Annu. Rev. Phys. Chem. |

19. | A. J. Nozik, “Multiple exciton generation in semiconductor quantum dots,” Chem. Phys. Lett. |

20. | J. A. McGuire, J. Joo, J. M. Pietryga, R. D. Schaller, and V. I. Klimov, “New aspects of carrier multiplication in semiconductor nanocrystals,” Acc. Chem. Res. |

21. | V. Kloper, R. Osovsky, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The growth of CdTe nanocrystals using in situ formed Cd0 crystalline particles,” J. Phys. Chem. C |

22. | R. Osovsky, V. Kloper, J. Kolny-Olesiak, A. Sashchiuk, and E. Lifshitz, “The Influience of small deviation from a spherical shape on the electronic and optical properties of CdTe nanocrystal quantum dots,” J. Phys. Chem. C |

23. | H. Zhu, N Song, W. Rodriguez-Cordoba, and T. Lian, “Wave Function Engineering for Efficient Extraction of up to Nineteen Electrons from One CdSe/CdS Quasi-Type II Quantum Dot,” J. Am. Chem. Soc. |

24. | 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 |

25. | 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. |

26. | S. L. Sewall, R. R. Cooney, E. A. Dias, P. Tyagi, and P. Kambhampati, “State-resolved observation in real time of the structural dynamics of multiexcitons in semiconductor nanocrystals,” Phys. Rev. B |

27. | M. R. Salvador, M. A. Hines, and G. D. Scholes, “Exciton-bath coupling and inhomogeneous broadening in the optical spectroscopy of semiconductor quantum dots,” J. Chem. Phys. |

**OCIS Codes**

(190.4180) Nonlinear optics : Multiphoton processes

(190.4720) Nonlinear optics : Optical nonlinearities of condensed matter

(320.7100) Ultrafast optics : Ultrafast measurements

(320.7130) Ultrafast optics : Ultrafast processes in condensed matter, including semiconductors

**ToC Category:**

Nonlinear Optics

**History**

Original Manuscript: July 31, 2013

Manuscript Accepted: September 3, 2013

Published: October 3, 2013

**Citation**

Andrey Gandman, Michal Bronstein-Tojen, Viki Kloper, Merav Muallem, Diana Yanover, Efrat Lifshitz, and Zohar Amitay, "Non-poissonian formation of multiple excitons in photoexcited CdTe colloidal quantum qots by femtosecond nonresonant two-photon absorption," Opt. Express **21**, 24300-24308 (2013)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-20-24300

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### References

- V. I. Klimov, Nanocrystal Quantum Dots (CRC, 2010). [CrossRef]
- E. R. Thoen, E. M. Koontz, M. Joschko, P. Langlois, T. R. Schibli, F. X. Kartner, E. P. Ippen, and L. A. Kolodziejski, “Two-photon absorption in semiconductor saturable absorber mirrors,” Appl. Phys. Lett.74, 3927 (1999). [CrossRef]
- D. R. Larson, W. R. Zipfel, R. M. Williams, S. W. Clark, M. P. Bruchez, F. W. Wise, and W. W. Webb, “Water-Soluble Quantum Dots for Multiphoton Fluorescence Imaging in Vivo,” Science300, 1434 (2003). [CrossRef] [PubMed]
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