OSA's Digital Library

Optical Materials Express

Optical Materials Express

  • Editor: David J. Hagan
  • Vol. 2, Iss. 5 — May. 1, 2012
  • pp: 519–525
« Show journal navigation

Solution processable and photopatternable blue, green and red quantum dots suitable for full color displays devices

Kyung Kook Jang, Prem Prabhakaran, Deepak Chandran, Jong-Jin Park, and Kwang-Sup Lee  »View Author Affiliations


Optical Materials Express, Vol. 2, Issue 5, pp. 519-525 (2012)
http://dx.doi.org/10.1364/OME.2.000519


View Full Text Article

Acrobat PDF (1158 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Core only of CdSe and core-shell quamtum dots (QDs) of CdS/ZnS, CdSe/ZnS and CdSe/ZnSe were functionalized with photosensitive monolayer to make them solution processable and photopatternable. Exchange of ligands was successfully followed using IR spectroscopic techniques. Core-shell type QDs were found to have better photoluminescence properties. Upon exposure to ultraviolet radiation these material were found to undergo polymerization forming interconnected arrays of QDs. These materials were found suitable for spin casting on organic and inorganic substrates. A highly efficient flourene-based two-photon sensitizer was mixed with QD dispersion of a urethane acrylate resin. Two-photon nanostereolithography using a mode-locked Ti:sapphire laser was applied on this resin mixture to fabricate three-dimensional (3D) microstructure. 3D microstructures fabricated were found with uniform dispersion of RGB QDs when observed through confocal microscope.

© 2012 OSA

1. Introduction

Quantum dots (QDs) are tiny crystals that can trap electrons on a spatial scale as they are small enough for making the quantum effects so evident. These nanocrystals (NCs) are playing an increasingly important role in semiconductor, optical and electronic devices. Controlled fabrication of two-dimensional (2D) or three-dimensional (3D) micro- and nanoscale structures containing QDs is of great scientific importance for the development of efficient optoelectronic devices [1

1. A. M. Brozell, M. A. Muha, A. Abed-Amoli, D. Bricarello, and A. N. Parikh, “Patterned when wet: environment-dependent multifunctional patterns within amphiphilic colloidal crystals,” Nano Lett. 7(12), 3822–3826 (2007). [CrossRef] [PubMed]

,2

2. V. L. Colvin, M. C. Schlamp, and A. P. Alivisatos, “Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer,” Nature 370(6488), 354–357 (1994). [CrossRef]

]. In recent years there have been commendable attempts to incorporate quantum dot 2D and 3D patterns through lithographic techniques [3

3. S. Jun, E. Jang, J. Park, and J. Kim, “Photopatterned semiconductor nanocrystals and their electroluminescence from hybrid light-emitting devices,” Langmuir 22(6), 2407–2410 (2006). [CrossRef] [PubMed]

,4

4. K. Aoki, D. Guimard, M. Nishioka, M. Nomura, S. Iwamoto, and Y. Arakawa, “Coupling of quantum-dot light emission with a three-dimensional photonic-crystal nanocavity,” Nat. Photonics 2(11), 688–692 (2008). [CrossRef]

]. Our group previously has reported the designing and synthesis of functionalized stable green emitting CdSe/ZnS quantum dots composed of a photopolymerizable outer corona constituting methacrylate and an inner siloxane layer, which are suitable for solution processing on both inorganic and organic substrates and their subsequent photopatterning in polymeric 3D shining microstructures [5

5. J.-J. Park, P. Prabhakaran, K. K. Jang, Y. Lee, J. Lee, K. Lee, J. Hur, J.-M. Kim, N. Cho, Y. Son, D.-Y. Yang, and K.-S. Lee, “Photopatternable quantum dots forming quasi-ordered arrays,” Nano Lett. 10(7), 2310–2317 (2010). [CrossRef] [PubMed]

]. In this work we are extending our previously reported method as a new way to create a solution processable RGB microstructure using photopatternable blue emitting CdS/ZnS and red emitting CdSe/ZnSe QDs along with the CdSe/ZnS green dots.

2. Experimental

2.1 Materials

Cadmium oxide (CdO, 99.99%), zinc acetate (99.9%, powder), selenium (99.9%, powder), sulfur (99.9%, powder), trioctylphosphine (TOP, 90%), oleic acid (OA, 90%), 1-octadecene (ODE, 90%), 11-mercapto-1-undecanol, 3-(trimethoxysilyl)propyl methacrylate, undecane-thiol (99.9%), trimethoxy(octyl)silane and anhydrous dimethyl sulfoxide (DMSO, 99.9 + %) were all purchased from Sigma-Aldrich and used without further purification. The urethane-acrylate resin SCR 500 was kindly provided by JSR Company, Japan.

2.2 Synthesis of CdS/ZnS, CdSe/ZnS and CdSe/ZnSe nanocrystals

The blue, green and red CdS, CdSe, CdS/ZnS, CdSe/ZnS and CdSe/ZnSe QDs respectively were synthesized by following the reported procedures [6

6. W. K. Bae, M. K. Nam, K. Char, and S. Lee, “Gram-scale one-pot synthesis of highly luminescent blue emitting Cd1−xZnxS/ZnS nanocrystals,” Chem. Mater. 20(16), 5307–5313 (2008) (and the references cited therein). [CrossRef]

8

8. W. K. Bae, K. Char, H. Hur, and S. Lee, “Single-step synthesis of quantum dots with chemical composition gradients,” Chem. Mater. 20(2), 531–539 (2008) (and the references cited therein). [CrossRef]

]. Relative quantum yield reported for core-shell QDs are 80% for blue and green, and 60% for red dot.

2.3 Synthesis of siloxane-containing methyl methacrylate terminated QDs

Oleic acid stabilized QDs (5 mg) and 50 mg of 11-mercapto-1-undecanol were dispersed in 5 mL chloroform and 5 mL ethanol under sonication for 3 hours. Chloroform (40 mL) was added into the mixture to precipitate the 11-mercapto-1-undecanol capped NCs. The material was soluble in ethanol and DMSO. 20 mg of 11-mercapto-1-undecanol capped QDs were first dispersed in 5 mL of dry DMSO. A total of 20 mg of 11-mercapto-1-undecanol capped nanoparticles were first dispersed in 5 mL of dry DMSO, and then 100 μL of 3-(trimethoxysilyl)propyl methacrylate was added. The mixture was stirred at 50°C for 6 hours. The resulting nanoparticles were precipitated with chloroform by centrifugation. The silane containing methacrylate terminated nanoparticles were then washed with methanol and chloroform.

2.4 Microfabrication

Setup for two-photon lithography

A mode-locked Ti:sapphire laser operating at 780 nm and 80 MHz with a pulse width of less than 100 fs was used as a source for two-photon stereolithography. A high-numerical aperture lens (NA = 1.4, with immersion oil), capable of high-resolution 3D addressing of points within the photopolymerizable material, was employed in the optical system.

Details of the confocal microscopy

Carl-Zeiss LSM5 Live confocal microscope containing external fluorescence lamps with different excitation wavelengths, namely, 405, 588, and 532 respectively for green, red, and blue photoactive materials was used.

3. Results and discussion

3.1 Synthesis

These core only and core-shell structures were examined for their PL efficiencies. Samples with comparable absorbance values in UV-vis spectra were analyzed and found with relatively very low PL for the core only structures. It is quite natural for the core only structures, as shell growth give additional advantage of better quantum confinement for the NCs [13

13. X. Peng, M. C. Schlamp, A. V. Kadavanich, and A. P. Alivisatos, “Epitaxial growth of highly luminescent CdSe/CdS core/shell nanocrystals with photostability and electronic accessibility,” J. Am. Chem. Soc. 119(30), 7019–7029 (1997). [CrossRef]

]. Growing a shell of higher band gap over the nanocrystals confines the wave function of the electron-hole pairs more precisely resulting in a stable core-shell structure for the nanocrystals. Appearance of CdSe and CdSe/ZnSe NCs under visible light and 365 nm UV irradiation is given in Fig. 2
Fig. 2 Photopatternable (a) CdSe and (b) CdSe/ZnSe NCs when observed under visible light. Photopatternable (c) CdSe and (d) CdSe/ZnSe NCs when observed under 365 nm UV light.
.Based on the result of Fig. 1, 3D structures by two-photon lithography were fabricated with core only and core-shell structures (Details of 3D structure fabrication are described in the later part of this manuscript). Through an optical microscope brightness of these structures were observed under 365 nm UV irradiation. In Fig. 3
Fig. 3 (a) CAD master image used to prepare the 3D woodpile pattern; (b) SEM image of typical 3D pattern; (c) and (d), PL micrographs observed by 3D patterns of photocured single shell QD of CdSe and CdSe/ZnS NCs, respectively, when observed under 365 nm UV exposure.
, panels (c) and (d) shows microstructures thus fabricated based on CdSe and CdSe/ZnS QDs respectively. The core-shell structures were appeared with higher luminescence brightness as appeared in the figure. For rest of the study photopatternable core-shell type nanocrystals were used due to their better PL properties compared the core only structures.

3.2 Characterizations

Figure 4
Fig. 4 UV-vis and PL spectra of photopatternable QDs. (a) blue Cd/ZnS dots, (b) green CdSe/ZnS dots, (c) red CdSe/ZnSe dots, (d) photograph of the corresponding samples under UV light.
shows the absorption and photoluminescence spectra of different functionalized QD nanocrystals grown with different core-shell composition and with identical surface ligand conditions. The samples were observed to have relatively monodisperse particle size from the full width at half maximum (FWHM) of the PL spectra. The ligand exchange over the QD surfaces is evidenced from their IR spectra as depicted in Fig. 5
Fig. 5 IR spectra of oleic acid ligated QDs and photopatternable QDs.
, which shows the ligand exchange over QDs with green emission. Oleic acid ligated QDs were characterized with intense signals corresponding to the antisymmetric ν(CO) stretching vibration bands of carboxylate around 1,555 cm−1 with no detectable presence of carboxylic groups (1,710 cm−1) [14

14. L. J. Bellamy, The Infrared Spectra of Complex Molecules: Advances in Infrared Group Frequencies (Chapman and Hall, 1980), Vol. 2.

]. It also displays two bands at 2922 and 2850 cm−1 corresponding to the ν(CH) vibrations of CH2 groups. For the QDs with photopatternable ligands, absence of the characteristic peak at 2500 cm−1 for S-H stretching indicates the formation of QD-S bond on the surface of the NCs. Appearance of a new band around 1070 cm−1 is observed which corresponds to the Si-O-Si vibrations.

3.3 Microfabrication

Different lithographic techniques those have been employed in the past to achieve quantum dot embedded 3D microstructures had a pre-existing problem of detrimental aggregation effect when lithography was attempted by mixing photopatternable materials with QDs [9

9. C. Ingrosso, V. Fakhfouri, M. Striccoli, A. Agostiano, A. Voigt, G. Gruetzner, M. L. Curri, and J. Brugger, “An epoxy photoresist modified by luminescent nanocrystals for the fabrication of 3D high-aspect-ratio microstructures,” Adv. Funct. Mater. 17(13), 2009–2017 (2007). [CrossRef]

12

12. Y. Dirix, C. Bastiaansen, W. Caseri, and P. Smith, “Preparation, structure and properties of uniaxially oriented polyethylene-silver nanocomposites,” J. Mater. Sci. 34(16), 3859–3866 (1999). [CrossRef]

]. These effects are governed by the interactions between the surface ligands of the QDs, as well as their incompatibility with the photopatternable material in which they are dispersed.

We have successfully demonstrated that the acrylate-terminated QDs could be integrated well into acrylate and urethane acrylate resins due to their photopatternable corona and can be used for two-photon lithography (TPL) to fabricate microstructures. TPL is a fast-prototyping method that photoinduces chemical reactions in a patternable medium, allowing direct writing of microstructures. Femtosecond lasers with high repetition rates induce very specific chemical changes at the focal spot of the laser within a photoactive medium. Two-photon sensitivity is key for initiating chemical changes during microfabrication. For this reason, the patternable medium should contain a two-photon absorbing (TPA) material acting as a photosensitizer or an photoinitiator.

The spatial selectivity of the chemical process arises from the inverse dependence of two-photon absorption on the intensity of the laser beam. The two-photon dye used as the photosensitizer (spirofluorene-based TPA dye) was chosen such that the peak fluorescence of the dye does not coincide with that of the QD fluorescence during imaging the QD-impregnated structures. The fabricated structures were visualized by confocal microscopy. A Carl Zeiss LSM5 Live confocal microscope was used for visualization and the images are summarized in panels (a)-(d) in Fig. 6
Fig. 6 Confocal microscope images of 3D structure, demonstrating the uniform incorporation of RGB quantum dots throughout the structure.
. For the measurement of panel (a) visible laser line of 405 was used along with 415-480 nm filter and for panel (b) the visible laser line used was that of 488 nm and the filter was that of 500-525 nm wavelength. In the case of panel (c) it was done with laser line 532 nm in combination with a filter 550 nm-IR wavelength. Finally for the panel (d) the measurement was with all these three laser lines in operation with no filters to get white emission properties. The images discern the successful and uniform incorporation of nanocrystals within the microstructure.

The (a)-(d) panels in Fig. 6 shows the potential of these functionalized nanomaterials for their utilization in full color display devices. Charge transport layers consist of molecules or polymers having photocurable prosthetic groups such as oxetane or methacrylate can very well suited to utilize these materials for full color display device fabrication [15

15. J. Y. Park, J. Lee, and J.-B. Kim, “Photo-patternable electroluminescent blends of polyfluorene derivatives and charge-transporting molecules,” Eur. Polym. J. 44(12), 3981–3986 (2008). [CrossRef]

,16

16. J. V. Crivello, “Synergistic effects in hybrid free radical/cationic photopolymerizations,” J. Polym. Sci. A Polym. Chem. 45(16), 3759–3769 (2007). [CrossRef]

]. Attempts in this regard are in progress and the results will be reported in the due course.

4. Conclusion

Photopatternable RGB core only and core-shell type quantum dots with an inner siloxane layer and a photopatternable methacrylate corona were synthesized. The hybrid nature of the photopatternable QD makes it readily suitable for solution processing on both inorganic and organic substrates and subsequent photopatterning. Core-shell type nanocrystals were found with better PL properties. Chemical compatibility of photopatternable QD and the phenomenon of photodriven ordering in functionalized QDs was used to fabricate microstructure with uniform quantum dot dispersion. Confocal microscope images showed a uniform distribution of RGB QDs all over the microstructure.

Acknowledgments

This work was supported by the Mid-career Researcher Program (No. 2010-0000499) and the Active Polymer Center for Patterned Integration (ERC R 11-2007-050-01002-0) of the National Research Foundation of Korea. One of us, K.-S. Lee, thanks to the Asian Office of Aerospace Research and Development (AOARD), Air Force Office of Scientific Research, USA, for their support.

References and links

1.

A. M. Brozell, M. A. Muha, A. Abed-Amoli, D. Bricarello, and A. N. Parikh, “Patterned when wet: environment-dependent multifunctional patterns within amphiphilic colloidal crystals,” Nano Lett. 7(12), 3822–3826 (2007). [CrossRef] [PubMed]

2.

V. L. Colvin, M. C. Schlamp, and A. P. Alivisatos, “Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer,” Nature 370(6488), 354–357 (1994). [CrossRef]

3.

S. Jun, E. Jang, J. Park, and J. Kim, “Photopatterned semiconductor nanocrystals and their electroluminescence from hybrid light-emitting devices,” Langmuir 22(6), 2407–2410 (2006). [CrossRef] [PubMed]

4.

K. Aoki, D. Guimard, M. Nishioka, M. Nomura, S. Iwamoto, and Y. Arakawa, “Coupling of quantum-dot light emission with a three-dimensional photonic-crystal nanocavity,” Nat. Photonics 2(11), 688–692 (2008). [CrossRef]

5.

J.-J. Park, P. Prabhakaran, K. K. Jang, Y. Lee, J. Lee, K. Lee, J. Hur, J.-M. Kim, N. Cho, Y. Son, D.-Y. Yang, and K.-S. Lee, “Photopatternable quantum dots forming quasi-ordered arrays,” Nano Lett. 10(7), 2310–2317 (2010). [CrossRef] [PubMed]

6.

W. K. Bae, M. K. Nam, K. Char, and S. Lee, “Gram-scale one-pot synthesis of highly luminescent blue emitting Cd1−xZnxS/ZnS nanocrystals,” Chem. Mater. 20(16), 5307–5313 (2008) (and the references cited therein). [CrossRef]

7.

H. Song and S. Lee, “Red light emitting solid state hybrid quantum dot–near-UV GaN LED devices,” Nanotechnology 18(25), 255202 (2007) (and the references cited therein). [CrossRef]

8.

W. K. Bae, K. Char, H. Hur, and S. Lee, “Single-step synthesis of quantum dots with chemical composition gradients,” Chem. Mater. 20(2), 531–539 (2008) (and the references cited therein). [CrossRef]

9.

C. Ingrosso, V. Fakhfouri, M. Striccoli, A. Agostiano, A. Voigt, G. Gruetzner, M. L. Curri, and J. Brugger, “An epoxy photoresist modified by luminescent nanocrystals for the fabrication of 3D high-aspect-ratio microstructures,” Adv. Funct. Mater. 17(13), 2009–2017 (2007). [CrossRef]

10.

R. Shenhar, E. Jeoung, S. Srivastava, T. B. Norsten, and V. M. Rotello, “Crosslinked nanoparticle stripes and hexagonal networks obtained via selective patterning of block copolymer thin films,” Adv. Mater. 17(18), 2206–2210 (2005). [CrossRef]

11.

M. Gianini, W. R. Caseri, and U. W. Suter, “Polymer nanocomposites containing superstructures of self-organized platinum colloids,” J. Phys. Chem. B 105(31), 7399–7404 (2001). [CrossRef]

12.

Y. Dirix, C. Bastiaansen, W. Caseri, and P. Smith, “Preparation, structure and properties of uniaxially oriented polyethylene-silver nanocomposites,” J. Mater. Sci. 34(16), 3859–3866 (1999). [CrossRef]

13.

X. Peng, M. C. Schlamp, A. V. Kadavanich, and A. P. Alivisatos, “Epitaxial growth of highly luminescent CdSe/CdS core/shell nanocrystals with photostability and electronic accessibility,” J. Am. Chem. Soc. 119(30), 7019–7029 (1997). [CrossRef]

14.

L. J. Bellamy, The Infrared Spectra of Complex Molecules: Advances in Infrared Group Frequencies (Chapman and Hall, 1980), Vol. 2.

15.

J. Y. Park, J. Lee, and J.-B. Kim, “Photo-patternable electroluminescent blends of polyfluorene derivatives and charge-transporting molecules,” Eur. Polym. J. 44(12), 3981–3986 (2008). [CrossRef]

16.

J. V. Crivello, “Synergistic effects in hybrid free radical/cationic photopolymerizations,” J. Polym. Sci. A Polym. Chem. 45(16), 3759–3769 (2007). [CrossRef]

OCIS Codes
(110.3960) Imaging systems : Microlithography
(230.5590) Optical devices : Quantum-well, -wire and -dot devices
(250.5230) Optoelectronics : Photoluminescence

ToC Category:
Fluorescent and Luminescent Materials

History
Original Manuscript: February 21, 2012
Revised Manuscript: March 24, 2012
Manuscript Accepted: March 24, 2012
Published: April 2, 2012

Virtual Issues
Quantum Dots for Photonic Applications (2012) Optical Materials Express

Citation
Kyung Kook Jang, Prem Prabhakaran, Deepak Chandran, Jong-Jin Park, and Kwang-Sup Lee, "Solution processable and photopatternable blue, green and red quantum dots suitable for full color displays devices," Opt. Mater. Express 2, 519-525 (2012)
http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-2-5-519


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. A. M. Brozell, M. A. Muha, A. Abed-Amoli, D. Bricarello, and A. N. Parikh, “Patterned when wet: environment-dependent multifunctional patterns within amphiphilic colloidal crystals,” Nano Lett.7(12), 3822–3826 (2007). [CrossRef] [PubMed]
  2. V. L. Colvin, M. C. Schlamp, and A. P. Alivisatos, “Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer,” Nature370(6488), 354–357 (1994). [CrossRef]
  3. S. Jun, E. Jang, J. Park, and J. Kim, “Photopatterned semiconductor nanocrystals and their electroluminescence from hybrid light-emitting devices,” Langmuir22(6), 2407–2410 (2006). [CrossRef] [PubMed]
  4. K. Aoki, D. Guimard, M. Nishioka, M. Nomura, S. Iwamoto, and Y. Arakawa, “Coupling of quantum-dot light emission with a three-dimensional photonic-crystal nanocavity,” Nat. Photonics2(11), 688–692 (2008). [CrossRef]
  5. J.-J. Park, P. Prabhakaran, K. K. Jang, Y. Lee, J. Lee, K. Lee, J. Hur, J.-M. Kim, N. Cho, Y. Son, D.-Y. Yang, and K.-S. Lee, “Photopatternable quantum dots forming quasi-ordered arrays,” Nano Lett.10(7), 2310–2317 (2010). [CrossRef] [PubMed]
  6. W. K. Bae, M. K. Nam, K. Char, and S. Lee, “Gram-scale one-pot synthesis of highly luminescent blue emitting Cd1−xZnxS/ZnS nanocrystals,” Chem. Mater.20(16), 5307–5313 (2008) (and the references cited therein). [CrossRef]
  7. H. Song and S. Lee, “Red light emitting solid state hybrid quantum dot–near-UV GaN LED devices,” Nanotechnology18(25), 255202 (2007) (and the references cited therein). [CrossRef]
  8. W. K. Bae, K. Char, H. Hur, and S. Lee, “Single-step synthesis of quantum dots with chemical composition gradients,” Chem. Mater.20(2), 531–539 (2008) (and the references cited therein). [CrossRef]
  9. C. Ingrosso, V. Fakhfouri, M. Striccoli, A. Agostiano, A. Voigt, G. Gruetzner, M. L. Curri, and J. Brugger, “An epoxy photoresist modified by luminescent nanocrystals for the fabrication of 3D high-aspect-ratio microstructures,” Adv. Funct. Mater.17(13), 2009–2017 (2007). [CrossRef]
  10. R. Shenhar, E. Jeoung, S. Srivastava, T. B. Norsten, and V. M. Rotello, “Crosslinked nanoparticle stripes and hexagonal networks obtained via selective patterning of block copolymer thin films,” Adv. Mater.17(18), 2206–2210 (2005). [CrossRef]
  11. M. Gianini, W. R. Caseri, and U. W. Suter, “Polymer nanocomposites containing superstructures of self-organized platinum colloids,” J. Phys. Chem. B105(31), 7399–7404 (2001). [CrossRef]
  12. Y. Dirix, C. Bastiaansen, W. Caseri, and P. Smith, “Preparation, structure and properties of uniaxially oriented polyethylene-silver nanocomposites,” J. Mater. Sci.34(16), 3859–3866 (1999). [CrossRef]
  13. X. Peng, M. C. Schlamp, A. V. Kadavanich, and A. P. Alivisatos, “Epitaxial growth of highly luminescent CdSe/CdS core/shell nanocrystals with photostability and electronic accessibility,” J. Am. Chem. Soc.119(30), 7019–7029 (1997). [CrossRef]
  14. L. J. Bellamy, The Infrared Spectra of Complex Molecules: Advances in Infrared Group Frequencies (Chapman and Hall, 1980), Vol. 2.
  15. J. Y. Park, J. Lee, and J.-B. Kim, “Photo-patternable electroluminescent blends of polyfluorene derivatives and charge-transporting molecules,” Eur. Polym. J.44(12), 3981–3986 (2008). [CrossRef]
  16. J. V. Crivello, “Synergistic effects in hybrid free radical/cationic photopolymerizations,” J. Polym. Sci. A Polym. Chem.45(16), 3759–3769 (2007). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited