Abstract

Hybrid nanocomposites of cadmium sulfide (CdS) quantum dots and poly(propyleneimine) dendrimer having a 1,4-diaminobutane core have been produced by colloidal synthesis in degassed methanol at room temperature using third-, fourth-, and fifth-generation (G5.0) dendrimers, and their spectroscopic properties have been investigated. The nanoparticles fluoresced from 375 to 650nm under near-ultraviolet excitation, and their absorption spectra exhibited a strong blueshift of the band edge compared to that of the bulk CdS. The stability of nanocomposites depended significantly, while the size and spectroscopic properties exhibited a weaker dependence, on the dendrimer generation. Most compact and stable nanoparticles were obtained with G5.0 dendrimers. Average diameter was estimated to be 2.2±0.3nm, assuming nanoparticles of spherical shape within an infinite well potential. The room-temperature luminescence has a fast component with 165±5ps lifetime and a slow component with a 40±2ns lifetime. The luminescence is partially polarized with an initial anisotropy of 0.39±0.02.

© 2007 Optical Society of America

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  1. V. M. Agranovich, D. M. Basko, G. C. La Rocca, and F. Bassani, "Excitons and optical nonlinearities in hybrid organic-inorganic nanostructures," J. Phys. Condens. Matter 10, 9369-9400 (1998).
    [CrossRef]
  2. N. Q. Huong and J. L. Birman, "Quantum dot lattice embedded in an organic medium: hybrid exciton state and optical response," Phys. Rev. B 61, 13131-13136 (1999).
    [CrossRef]
  3. 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, 314-317 (2000).
    [CrossRef] [PubMed]
  4. A. P. Alivisatos, W. Gu, and C. Larabell, "Quantum dots as cellular probes," Annu. Rev. Biomed. Eng. 7, 55-76 (2005).
    [CrossRef] [PubMed]
  5. C. F. Landes, M. Braun, and M. A. El-Sayed, "On the nanoparticle to molecular size transition: fluorescence quenching studies," J. Phys. Chem. B 10, 10554-10558 (2001).
    [CrossRef]
  6. W. C. W. Chan and S. Nie, "Quantum dot bioconjugates for ultrasensitive nonisotopic detection," Science 281, 2016-2018 (1998).
    [CrossRef] [PubMed]
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  8. Al. L. Efros and A. L. Efros, "Interband absorption of light in a semiconductor sphere," Fiz. Tekh. Poluprovodn. (S.-Peterburg) 16, 1209-1214 (1982) Al. L. Efros and A. L. Efros,[Sov. Phys. Semicond. 16, 772-775 (1982).]
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    [CrossRef]
  11. L. Peng, C. Chen, C. R. Gonzalez, and V. Balogh-Nair, "Bioorganic studies in AIDS: synthetic antifungals against Pneumocystis carinii based on the multivalency concept," Int. J. Mol. Sci. 3, 1145-1161 (2002).
    [CrossRef]
  12. K. Sooklal, L. H. Hanus, H. J. Ploehn, and C. J. Murphy, "A blue emitting CdS-dendrimer nanocomposite," Adv. Mater. (Weinheim, Ger.) 10, 1083-1087 (1998).
    [CrossRef]
  13. B. I. Lemon and R. M. Crooks, "Preparation and characterization of dendrimer-encapsulated CdS semiconductor quantum dots," J. Am. Chem. Soc. 122, 12886-12887 (2000).
    [CrossRef]
  14. The bandgaps of CdS at 300K for both the wurzite and zinc-blende structures are given to be 2.42eV and 2.5eV.
  15. S. M. Sze, Physics of Semiconductor Devices (Wiley Interscience, 1981), pp. 848-849.
  16. "Veeco Learning Center--Lattice Parameters and Bandgap data," http://www.veeco.com/learning/learninglowbarlattice.asp
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
  22. M. O'Neil, J. Marohn, and G. McLendon, "Dynamics of electron hole pair recombination in semiconductor clusters," J. Phys. Chem. B 94, 4356-4363 (1990).
  23. N. Chestnoy, T. D. Harris, R. Hull, and L. E. Brus, "Luminescence and photophysics of CdS semiconductor clusters: the nature of the emitting electronic state," J. Phys. Chem. B 90, 3393-3399 (1986).
  24. J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 2nd ed. (Kluwer Academic/Plenum, 1999), pp. 291-366.
  25. N. Q. Huong and J. L. Birman, "Hybrid exciton state in a quantum dot-dendrite system: Green functions," Phys. Rev. B 67, 075313 (2003).
    [CrossRef]
  26. M. G. Bawendi, W. L. Wilson, L. Rothberg, P. J. Carroll, T. M. Jedju, M. L. Steigerwald, and L. E. Brus, "Electronic structure and photoexcited-carrier dynamics in nanometer-size CdSe clusters," Phys. Rev. Lett. 65, 1623-1626 (1990).
    [CrossRef] [PubMed]
  27. Y. Wang, "Photophysical and photochemical processes in semiconductor nanoclusters," in Advances in Photochemistry, D. C. Neckers, D. H. Volman, and G. von Bunau, eds. (Wiley, 1995), Vol. 19, pp. 179-233.
  28. M. Bruchez, Jr., M. Moronne, P. Gin, S. Weiss, and A. P. Alivisatos, "Semiconductor nanocrystals as fluorescent biological labels," Science 281, 2013-2016 (1998).
    [CrossRef] [PubMed]
  29. C. B. Murray, D. J. Norris, and M. G. Bawendi, "Synthesis and characterization of nearly monodisperse CdE (E=S,Se,Te), semiconductor nanocrystallites," J. Am. Chem. Soc. 11, 8706-8715 (1993).
    [CrossRef]
  30. M. Nirmal and L. Brus, "Luminescence photophysics in semiconductor nanocrystals," Acc. Chem. Res. 32, 407-414 (1999).
    [CrossRef]
  31. M. G. Bawendi, P. J. Carroll, W. L. Wilson, and L. E. Brus, "Luminescence properties of CdSe quantum crystallites: resonance between interior and surface localized states," J. Chem. Phys. 96, 946-954 (1992).
    [CrossRef]
  32. M. Nirmal, C. B. Murray, and M. G. Bawendi, "Fluorescence-linen arrowing in CdSe quantum dots: surface localization of the photogenerated exciton," Phys. Rev. B 50, 2293-2300 (1994).
    [CrossRef]
  33. Al. L. Efros, M. Rosen, M. Kuno, M. Nirmal, D. J. Norris, and M. Bawendi, "Band-edge exciton in quantum dots of semiconductors with a degenerate valence band: dark and bright exciton states," Phys. Rev. B 54, 4843-4856 (1996).
    [CrossRef]
  34. J. R. Lakowicz, I. Gryczynski, Z. Gryczynski, K. Nowaczyk, and C. J. Murphy, "Time-resolved spectral observations of cadmium-enriched cadmium sulfide nanoparticles and the effect of DNA oligomer binding," Anal. Biochem. 280, 128-136 (2000).
    [CrossRef] [PubMed]
  35. F. Pellegrino, P. Sekuler, and R. R. Alfano, "Temperature dependence of the 735nm fluorescence kinetics from spinach measured by picosecond laser streak camera system," Photochem. Photobiophys. 2, 15-23 (1983).
  36. A. Szabo, "Theory of polarized fluorescent emission in uniaxial liquid crystals," J. Chem. Phys. 72, 4620-4626 (1980).
    [CrossRef]
  37. J. Hu, L. Li, W. Yang, L. Manna, L. Wang, and A. P. Alivisatos, "Linearly polarized emission from colloidal semiconductor quantum rods," Science 292, 2060-2063 (2001).
    [CrossRef] [PubMed]
  38. X. Peng, L. Manna, W. Yang, J. Wickham, E. Sher, A. Kadavanich, and A. P. Alivisatos, "Linearly polarized emission from colloidal semiconductor quantum rods," Nature 404, 59-61 (2001).
    [CrossRef]
  39. S. Kan, T. Mokari, E. Rothenberg, and U. Banin, "Synthesis and size-dependent properties of zinc-blende semiconductor quantum rods," Nat. Mater. 2, 155-158 (2003).
    [CrossRef] [PubMed]

2005

A. P. Alivisatos, W. Gu, and C. Larabell, "Quantum dots as cellular probes," Annu. Rev. Biomed. Eng. 7, 55-76 (2005).
[CrossRef] [PubMed]

2003

N. Q. Huong and J. L. Birman, "Hybrid exciton state in a quantum dot-dendrite system: Green functions," Phys. Rev. B 67, 075313 (2003).
[CrossRef]

S. Kan, T. Mokari, E. Rothenberg, and U. Banin, "Synthesis and size-dependent properties of zinc-blende semiconductor quantum rods," Nat. Mater. 2, 155-158 (2003).
[CrossRef] [PubMed]

2002

L. Peng, C. Chen, C. R. Gonzalez, and V. Balogh-Nair, "Bioorganic studies in AIDS: synthetic antifungals against Pneumocystis carinii based on the multivalency concept," Int. J. Mol. Sci. 3, 1145-1161 (2002).
[CrossRef]

2001

C. F. Landes, M. Braun, and M. A. El-Sayed, "On the nanoparticle to molecular size transition: fluorescence quenching studies," J. Phys. Chem. B 10, 10554-10558 (2001).
[CrossRef]

J. Hu, L. Li, W. Yang, L. Manna, L. Wang, and A. P. Alivisatos, "Linearly polarized emission from colloidal semiconductor quantum rods," Science 292, 2060-2063 (2001).
[CrossRef] [PubMed]

X. Peng, L. Manna, W. Yang, J. Wickham, E. Sher, A. Kadavanich, and A. P. Alivisatos, "Linearly polarized emission from colloidal semiconductor quantum rods," Nature 404, 59-61 (2001).
[CrossRef]

2000

J. R. Lakowicz, I. Gryczynski, Z. Gryczynski, K. Nowaczyk, and C. J. Murphy, "Time-resolved spectral observations of cadmium-enriched cadmium sulfide nanoparticles and the effect of DNA oligomer binding," Anal. Biochem. 280, 128-136 (2000).
[CrossRef] [PubMed]

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, 314-317 (2000).
[CrossRef] [PubMed]

B. I. Lemon and R. M. Crooks, "Preparation and characterization of dendrimer-encapsulated CdS semiconductor quantum dots," J. Am. Chem. Soc. 122, 12886-12887 (2000).
[CrossRef]

1999

A. W. Bosman, H. M. Janssen, and E. W. Meijer, "About dendrimers: structure, physical properties, and applications," Chem. Rev. (Washington, D.C.) 99, 1665-1688 (1999).
[CrossRef]

J. R. Lakowicz, I. Gryczynski, Z. Gryczynski, and C. J. Murphy, "Luminescence spectral properties of CdS nanoparticles," J. Phys. Chem. B 103, 7613-7620 (1999).
[CrossRef]

N. Q. Huong and J. L. Birman, "Quantum dot lattice embedded in an organic medium: hybrid exciton state and optical response," Phys. Rev. B 61, 13131-13136 (1999).
[CrossRef]

M. Nirmal and L. Brus, "Luminescence photophysics in semiconductor nanocrystals," Acc. Chem. Res. 32, 407-414 (1999).
[CrossRef]

1998

M. Bruchez, Jr., M. Moronne, P. Gin, S. Weiss, and A. P. Alivisatos, "Semiconductor nanocrystals as fluorescent biological labels," Science 281, 2013-2016 (1998).
[CrossRef] [PubMed]

V. M. Agranovich, D. M. Basko, G. C. La Rocca, and F. Bassani, "Excitons and optical nonlinearities in hybrid organic-inorganic nanostructures," J. Phys. Condens. Matter 10, 9369-9400 (1998).
[CrossRef]

W. C. W. Chan and S. Nie, "Quantum dot bioconjugates for ultrasensitive nonisotopic detection," Science 281, 2016-2018 (1998).
[CrossRef] [PubMed]

K. Sooklal, L. H. Hanus, H. J. Ploehn, and C. J. Murphy, "A blue emitting CdS-dendrimer nanocomposite," Adv. Mater. (Weinheim, Ger.) 10, 1083-1087 (1998).
[CrossRef]

1996

Al. L. Efros, M. Rosen, M. Kuno, M. Nirmal, D. J. Norris, and M. Bawendi, "Band-edge exciton in quantum dots of semiconductors with a degenerate valence band: dark and bright exciton states," Phys. Rev. B 54, 4843-4856 (1996).
[CrossRef]

1994

M. Nirmal, C. B. Murray, and M. G. Bawendi, "Fluorescence-linen arrowing in CdSe quantum dots: surface localization of the photogenerated exciton," Phys. Rev. B 50, 2293-2300 (1994).
[CrossRef]

1993

C. B. Murray, D. J. Norris, and M. G. Bawendi, "Synthesis and characterization of nearly monodisperse CdE (E=S,Se,Te), semiconductor nanocrystallites," J. Am. Chem. Soc. 11, 8706-8715 (1993).
[CrossRef]

1992

M. G. Bawendi, P. J. Carroll, W. L. Wilson, and L. E. Brus, "Luminescence properties of CdSe quantum crystallites: resonance between interior and surface localized states," J. Chem. Phys. 96, 946-954 (1992).
[CrossRef]

1990

M. G. Bawendi, W. L. Wilson, L. Rothberg, P. J. Carroll, T. M. Jedju, M. L. Steigerwald, and L. E. Brus, "Electronic structure and photoexcited-carrier dynamics in nanometer-size CdSe clusters," Phys. Rev. Lett. 65, 1623-1626 (1990).
[CrossRef] [PubMed]

M. O'Neil, J. Marohn, and G. McLendon, "Dynamics of electron hole pair recombination in semiconductor clusters," J. Phys. Chem. B 94, 4356-4363 (1990).

1987

L. Spanhel, M. Haase, H. Weller, and A. Henglein, "Photochemistry of colloidal semiconductors. Surface modification and stability of strong luminescing CdS particles," J. Am. Chem. Soc. 109, 5649-5655 (1987).
[CrossRef]

1986

N. Chestnoy, T. D. Harris, R. Hull, and L. E. Brus, "Luminescence and photophysics of CdS semiconductor clusters: the nature of the emitting electronic state," J. Phys. Chem. B 90, 3393-3399 (1986).

1984

L. E. Brus, "Electron-electron and electron-hole interactions in small semiconductor crystallites: the size dependence of the lowest excited electronic state," J. Chem. Phys. 80, 4403-4409 (1984).
[CrossRef]

1983

F. Pellegrino, P. Sekuler, and R. R. Alfano, "Temperature dependence of the 735nm fluorescence kinetics from spinach measured by picosecond laser streak camera system," Photochem. Photobiophys. 2, 15-23 (1983).

1982

Al. L. Efros and A. L. Efros, "Interband absorption of light in a semiconductor sphere," Fiz. Tekh. Poluprovodn. (S.-Peterburg) 16, 1209-1214 (1982) Al. L. Efros and A. L. Efros,[Sov. Phys. Semicond. 16, 772-775 (1982).]

1981

A. I. Ekimov and A. A. Onushchenko, "Quantum size effect in three-dimensional microscopic semiconductor crystals," JETP Lett. 34, 345-348 (1981).

1980

A. Szabo, "Theory of polarized fluorescent emission in uniaxial liquid crystals," J. Chem. Phys. 72, 4620-4626 (1980).
[CrossRef]

Acc. Chem. Res.

M. Nirmal and L. Brus, "Luminescence photophysics in semiconductor nanocrystals," Acc. Chem. Res. 32, 407-414 (1999).
[CrossRef]

Adv. Mater. (Weinheim, Ger.)

K. Sooklal, L. H. Hanus, H. J. Ploehn, and C. J. Murphy, "A blue emitting CdS-dendrimer nanocomposite," Adv. Mater. (Weinheim, Ger.) 10, 1083-1087 (1998).
[CrossRef]

Anal. Biochem.

J. R. Lakowicz, I. Gryczynski, Z. Gryczynski, K. Nowaczyk, and C. J. Murphy, "Time-resolved spectral observations of cadmium-enriched cadmium sulfide nanoparticles and the effect of DNA oligomer binding," Anal. Biochem. 280, 128-136 (2000).
[CrossRef] [PubMed]

Annu. Rev. Biomed. Eng.

A. P. Alivisatos, W. Gu, and C. Larabell, "Quantum dots as cellular probes," Annu. Rev. Biomed. Eng. 7, 55-76 (2005).
[CrossRef] [PubMed]

Chem. Rev. (Washington, D.C.)

A. W. Bosman, H. M. Janssen, and E. W. Meijer, "About dendrimers: structure, physical properties, and applications," Chem. Rev. (Washington, D.C.) 99, 1665-1688 (1999).
[CrossRef]

Fiz. Tekh. Poluprovodn. (S.-Peterburg)

Al. L. Efros and A. L. Efros, "Interband absorption of light in a semiconductor sphere," Fiz. Tekh. Poluprovodn. (S.-Peterburg) 16, 1209-1214 (1982) Al. L. Efros and A. L. Efros,[Sov. Phys. Semicond. 16, 772-775 (1982).]

Int. J. Mol. Sci.

L. Peng, C. Chen, C. R. Gonzalez, and V. Balogh-Nair, "Bioorganic studies in AIDS: synthetic antifungals against Pneumocystis carinii based on the multivalency concept," Int. J. Mol. Sci. 3, 1145-1161 (2002).
[CrossRef]

J. Am. Chem. Soc.

B. I. Lemon and R. M. Crooks, "Preparation and characterization of dendrimer-encapsulated CdS semiconductor quantum dots," J. Am. Chem. Soc. 122, 12886-12887 (2000).
[CrossRef]

L. Spanhel, M. Haase, H. Weller, and A. Henglein, "Photochemistry of colloidal semiconductors. Surface modification and stability of strong luminescing CdS particles," J. Am. Chem. Soc. 109, 5649-5655 (1987).
[CrossRef]

C. B. Murray, D. J. Norris, and M. G. Bawendi, "Synthesis and characterization of nearly monodisperse CdE (E=S,Se,Te), semiconductor nanocrystallites," J. Am. Chem. Soc. 11, 8706-8715 (1993).
[CrossRef]

J. Chem. Phys.

A. Szabo, "Theory of polarized fluorescent emission in uniaxial liquid crystals," J. Chem. Phys. 72, 4620-4626 (1980).
[CrossRef]

M. G. Bawendi, P. J. Carroll, W. L. Wilson, and L. E. Brus, "Luminescence properties of CdSe quantum crystallites: resonance between interior and surface localized states," J. Chem. Phys. 96, 946-954 (1992).
[CrossRef]

L. E. Brus, "Electron-electron and electron-hole interactions in small semiconductor crystallites: the size dependence of the lowest excited electronic state," J. Chem. Phys. 80, 4403-4409 (1984).
[CrossRef]

J. Phys. Chem. B

J. R. Lakowicz, I. Gryczynski, Z. Gryczynski, and C. J. Murphy, "Luminescence spectral properties of CdS nanoparticles," J. Phys. Chem. B 103, 7613-7620 (1999).
[CrossRef]

M. O'Neil, J. Marohn, and G. McLendon, "Dynamics of electron hole pair recombination in semiconductor clusters," J. Phys. Chem. B 94, 4356-4363 (1990).

N. Chestnoy, T. D. Harris, R. Hull, and L. E. Brus, "Luminescence and photophysics of CdS semiconductor clusters: the nature of the emitting electronic state," J. Phys. Chem. B 90, 3393-3399 (1986).

C. F. Landes, M. Braun, and M. A. El-Sayed, "On the nanoparticle to molecular size transition: fluorescence quenching studies," J. Phys. Chem. B 10, 10554-10558 (2001).
[CrossRef]

J. Phys. Condens. Matter

V. M. Agranovich, D. M. Basko, G. C. La Rocca, and F. Bassani, "Excitons and optical nonlinearities in hybrid organic-inorganic nanostructures," J. Phys. Condens. Matter 10, 9369-9400 (1998).
[CrossRef]

JETP Lett.

A. I. Ekimov and A. A. Onushchenko, "Quantum size effect in three-dimensional microscopic semiconductor crystals," JETP Lett. 34, 345-348 (1981).

Nat. Mater.

S. Kan, T. Mokari, E. Rothenberg, and U. Banin, "Synthesis and size-dependent properties of zinc-blende semiconductor quantum rods," Nat. Mater. 2, 155-158 (2003).
[CrossRef] [PubMed]

Nature

X. Peng, L. Manna, W. Yang, J. Wickham, E. Sher, A. Kadavanich, and A. P. Alivisatos, "Linearly polarized emission from colloidal semiconductor quantum rods," Nature 404, 59-61 (2001).
[CrossRef]

Photochem. Photobiophys.

F. Pellegrino, P. Sekuler, and R. R. Alfano, "Temperature dependence of the 735nm fluorescence kinetics from spinach measured by picosecond laser streak camera system," Photochem. Photobiophys. 2, 15-23 (1983).

Phys. Rev. B

N. Q. Huong and J. L. Birman, "Hybrid exciton state in a quantum dot-dendrite system: Green functions," Phys. Rev. B 67, 075313 (2003).
[CrossRef]

M. Nirmal, C. B. Murray, and M. G. Bawendi, "Fluorescence-linen arrowing in CdSe quantum dots: surface localization of the photogenerated exciton," Phys. Rev. B 50, 2293-2300 (1994).
[CrossRef]

Al. L. Efros, M. Rosen, M. Kuno, M. Nirmal, D. J. Norris, and M. Bawendi, "Band-edge exciton in quantum dots of semiconductors with a degenerate valence band: dark and bright exciton states," Phys. Rev. B 54, 4843-4856 (1996).
[CrossRef]

N. Q. Huong and J. L. Birman, "Quantum dot lattice embedded in an organic medium: hybrid exciton state and optical response," Phys. Rev. B 61, 13131-13136 (1999).
[CrossRef]

Phys. Rev. Lett.

M. G. Bawendi, W. L. Wilson, L. Rothberg, P. J. Carroll, T. M. Jedju, M. L. Steigerwald, and L. E. Brus, "Electronic structure and photoexcited-carrier dynamics in nanometer-size CdSe clusters," Phys. Rev. Lett. 65, 1623-1626 (1990).
[CrossRef] [PubMed]

Science

M. Bruchez, Jr., M. Moronne, P. Gin, S. Weiss, and A. P. Alivisatos, "Semiconductor nanocrystals as fluorescent biological labels," Science 281, 2013-2016 (1998).
[CrossRef] [PubMed]

J. Hu, L. Li, W. Yang, L. Manna, L. Wang, and A. P. Alivisatos, "Linearly polarized emission from colloidal semiconductor quantum rods," Science 292, 2060-2063 (2001).
[CrossRef] [PubMed]

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, 314-317 (2000).
[CrossRef] [PubMed]

W. C. W. Chan and S. Nie, "Quantum dot bioconjugates for ultrasensitive nonisotopic detection," Science 281, 2016-2018 (1998).
[CrossRef] [PubMed]

Other

J. M. J. Frechet and D. Tomalia, eds., Dendrimers and Other Dendritic Polymers (Wiley, 2001).
[CrossRef]

J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 2nd ed. (Kluwer Academic/Plenum, 1999), pp. 291-366.

The bandgaps of CdS at 300K for both the wurzite and zinc-blende structures are given to be 2.42eV and 2.5eV.

S. M. Sze, Physics of Semiconductor Devices (Wiley Interscience, 1981), pp. 848-849.

"Veeco Learning Center--Lattice Parameters and Bandgap data," http://www.veeco.com/learning/learninglowbarlattice.asp

J. Singh, Physics of Semiconductors and Their Heterostructures (McGraw-Hill, 1993).

D. W. Palmer, www.semiconductors.co.uk, 2002.06.

Y. Wang, "Photophysical and photochemical processes in semiconductor nanoclusters," in Advances in Photochemistry, D. C. Neckers, D. H. Volman, and G. von Bunau, eds. (Wiley, 1995), Vol. 19, pp. 179-233.

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Figures (8)

Fig. 1
Fig. 1

Room-temperature fluorescence spectra of hybrid CdS - DAB nanoparticles in methanol synthesized using G5.0, of a DAB dendrimer, and showing the effect of incremental additions of Cd 2 + and S 2 ions on the fluorescence emission (curves S1, S2, S3, S4, and S5). The concentration of Cd 2 + and S 2 ions in sample 1 (curve S1) was 3.84 × 10 4 M . Ions were added in shots of this 3.84 × 10 4 M solution to prepare other samples, so that ion concentrations in samples 2, 3, 4, and 5 were two, three, four, and five times, respectively, of that in sample 1. The concentration of the dendrimer in all the samples was 2.23 × 10 4 M .

Fig. 2
Fig. 2

Dependence of fluorescence signal on the dendrimer concentration, which was varied from 1.395 × 10 5 M ( 1 4 C ) to 5.58 × 10 4 M ( 10 C ) , while the concentration of Cd 2 + and S 2 ions was maintained constant at 1.92 × 10 3 M .

Fig. 3
Fig. 3

Room-temperature fluorescence spectra of CdS - DAB nanocomposites in methanol synthesized using G3.0, G4.0, and G5.0 of DAB dendrimers. The excitation wavelength was 266 nm .

Fig. 4
Fig. 4

Room-temperature absorption spectra of CdS - DAB nanocomposites in methanol synthesized using G3.0, G4.0, and G5.0 of DAB dendrimers. Spectra are corrected for the solvent absorption. Baselines of the absorption spectra of nanocomposites with G3.0 and G4.0 dendrimers are shifted vertically for clarity.

Fig. 5
Fig. 5

Dependence of the band-edge absorption peak position (in terms of wavelength in nanometers) on the diameter of the CdS QD estimated using the Brus effective mass model discussed in the text (solid curve). The three solid squares are experimental absorption band-edge peak positions of CdS -DAB nanocomposites in methanol synthesized using G3.0, G4.0, and G5.0 dendrimers displayed in Fig. 4. The dashed line corresponds to the room-temperature bandgap energy ( 2.42 eV ) of bulk CdS . Inset zooms on the section of the curve with experimental data points.

Fig. 6
Fig. 6

Room-temperature fluorescence decay dynamics of a CdS -DAB nanocomposite in methanol synthesized using G5.0 DAB dendrimer: (a) fast component measured using a streak camera, and (b) slow component measured using a photomultiplier tube and a 50 Ω terminated oscilloscope. The smooth curve is a single exponential fit to the experimental data represented by the wiggly curve in each of the two profiles.

Fig. 7
Fig. 7

Time evolution of fluorescence anisotropy of CdS -DAB in methanol (open squares) obtained using Eq. (3) and the temporal profiles of fluorescence parallel and perpendicular to the polarization of the excitation beam. The profiles of fluorescence polarized parallel (filled square) and perpendicular (open circles) are also shown. The measurements were carried out at room temperature.

Fig. 8
Fig. 8

Proposed partial energy-level diagram of the CdS -DAB nanocomposite in methanol synthesized using the G5.0 DAB dendrimer. (NR is the nonradiative relaxation.)

Tables (1)

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Table 1 Estimation of the Diameter of CdS -DAB Nanoparticles

Equations (3)

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E ( R ) = E g + 2 π 2 2 R 2 [ 1 m e + 1 m h ] 1.8 e 2 ε R ,
I ( t ) = I 1 exp ( t τ 1 ) + I s ( t ) ,
r ( t ) = [ I π ( t ) I σ ( t ) ] [ I π ( t ) + 2 I σ ( t ) ] ,

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