Article pubs.acs.org/IECR
Green Synthesis of CdSe Colloidal Nanocrystals with Strong Green Emission by the Sol−Gel Method Mohammad Reza Gaeeni,*,§ Marzieh Tohidian,‡ and Mohammad Majles-Ara§ §
Photonic Laboratory, Physics Department, Kharazmi University, 49 Mofateh Ave., P. O. Box 1571914911, Tehran, Iran Faculty of Medicine, Tehran University of Medical Sciences, PourSina Ave., P. O. Box 14155-6447, Tehran, Iran
‡
ABSTRACT: In this paper, high-quality CdSe colloidal nanocrystals were synthesized by an improved Sol−Gel green technique. These colloidal nanocrystals were characterized by different techniques: Transmission Electron Microscopy (TEM) showed that the diameter of colloidal nanocrystals is about 3 nm; X-ray diffraction (XRD) demonstrated that CdSe colloidal nanocrystals formed in cubic phase; Fourier Transform Infrared spectroscopy (FT-IR) was employed to study the chemical compounds of asprepared sol; UV−visible absorption spectroscopy was used to evaluate optical properties of prepared CdSe colloidal nanocrystals, which indicated that the absorption peak is around 500 nm; Photoluminescence (PL) spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 50.2% with 440 nm excitation wavelengths. Experimental observation has shown that highly stable CdSe colloidal nanocrystals with a strong green emission were synthesized. The mentioned optical properties have not been reported before. for health and with wide applications is inevitable.26−28 This means that highly stable sol with a controlled concentration ratio of precursor material is necessary.29 In order to do this, several particular factors, such as pH, concentration, and temperature, must be optimized to develop a sol−gel route for the preparation of highly stable CdSe colloidal nanocrystals.30 The goal of this research is to introduce a facile green sol−gel route for synthesis of highly stable CdSe colloidal nanocrystals that radiate a strong green emission. In addition, optical properties such as optical spectra, optical band gap, and refractive index of the colloidal CdSe nanostructures have been evaluated that have not been reported before.
1. INTRODUCTION Colloidal semiconductor nanocrystals have attracted broad attention and have been used in numerous applications such as light emitting diodes (LED),1 solar cells,2 single-electron transistor,3 and lasers.4 A fundamental reason for this has been the adjustability of the optoelectronic properties by controlling the crystal’s composition, shape, and size.5 The colloidal nanocrystals are also of much interest due to their nonlinear effects and fast optical response.6−8 Over the last 30 years, various colloidal nanomaterials have been developed; among them, the Cadmium Selenide (CdSe) nanostructure has been the subject of intense study. CdSe nanostructures (at various particle sizes) display a full range of visible light emission colors from deep red to blue, due to the blue-shift of the optical threshold.9,10 The CdSe nanocrystals have abundant practical applications as emitting materials in cancer targeting and imaging,11 colortunable LED,12 photovoltaic,13 and solar cells.14 A major goal that causes developing synthetic chemistry of CdSe colloidal semiconductor nanocrystals is controlling the luminescence quantum efficiency.15 Several methods have been reported for preparing colloidal CdSe nanocrystals, such as inverse micelle technique,16 Molecular Beam Epitaxy (MBE),17 Metal Organic Chemical Vapor Deposition (MOCVD),18 hydrothermal methods,19 and solvothermal methods.20 These methods usually need hard conditions such as toxic solvents and reagents and high temperature and are expensive, while the green sol−gel route does not have these conditions.21 Compared with the other routes, the sol−gel route has many advantages, such as low process temperature, high control of purity, repeatability, low cost, simplicity, and the homogeneity of the final product up to atomic scale.22,23 This approach is a particularly powerful tool for the synthesis of nanostructures with desired shape and size on the nanometer scale.24,25 However, the development of “green” synthesis for preparation of CdSe colloidal nanocrystals with minimum chemical hazards © 2014 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Materials. The starting materials were selenium powder (Se, 99.5% Aldrich), cadmium chloride (CdCl2, 99.99% Aldrich), sodium borohydride (NaBH4, 98% Aldrich), nitric acid (HNO3, 35% Merck), sodium hydroxide (NaOH, Aldrich), soluble starch (C12H22O11, Aldrich), and distilled water, were of analytical grade, and were purchased from Aldrich (USA). 2.2. Synthesize Method. In order to synthesize CdSe colloidal nanocrystals, 0.50 mmol of selenium powder was mixed with 30 mL of distilled water, and 1.22 mmol of sodium borohydride (NaBH4) was added to this solution. The solution was then stirred vigorously for 1 h at room temperature under an inert atmosphere. All of the selenium dissolved in water and after this stage the obtained solution turned into a clear colorless solution. In a typical room temperature preparation procedure, an aqueous solution of soluble starch (50 mL, 0.05 wt %) was Received: Revised: Accepted: Published: 7598
January 31, 2014 March 16, 2014 April 11, 2014 April 11, 2014 dx.doi.org/10.1021/ie5004398 | Ind. Eng. Chem. Res. 2014, 53, 7598−7603
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added to an aqueous solution of CdCl2 (5 mL, 16 × 10−3 M). Adding a few drops of nitric acid (HNO3) formed a clear solution with the pH value of 2. The reaction mixture was discharged into a round-bottom flask with vigorous stirring. Then 0.3 M sodium hydroxide solution was added to adjust the pH value from 2 to 11−12. This was followed by a slow addition of 3 mL (16 × 10−3 M) colorless selenide ion solution. The color of the solution changed immediately into transparent red upon addition of selenide ion solution, indicating the formation of CdSe colloidal nanoparticles. The solution was further stirred for 4 h at 70 °C and aged in an autoclave at 70 °C for 24 h. Since the chemical reaction is faster at 70 °C, aging can be accelerated by thermal treatment, which increases the rate of the condensation reaction.31 CdSe colloidal nanocrystals were obtained according to this procedure that the molar ratio of Cd:Se was 0.7:1.2. 2.3. Characterization. The absorption spectra of each solution was recorded after standing for 90 min. A CARY 500 SCAN UV−vis spectrophotometer was employed for absorbance measurements using quartz cells of path length 1 cm. The TEM investigations for the morphology of the samples were tested using the Philips CM250 FEG UltraTwin operated at 250 kV. Images were recorded with a Gatan model 794 CCDcamera. A Malvern Zetasizer Nano (ZEN3600) was employed for the particle size distribution measurements. Fourier transform infrared spectroscopy (FTIR) measurements of the samples were collected on a NEXU670 spectrometer with a spectral resolution of 1 cm−1. The crystallographic phases identification and estimation of the average crystallite size of samples were performed by X-ray diffractometer (XRD), Philips B.V (CuK- λ = 0.154 nm) radiation at 40 kV and 30 mA. The photoluminescence spectra of the samples were obtained by a GILDEN PHOTONICS FLUOROSENS spectrometer using quartz cells of path length 1 cm. All measurements were carried out at room temperature.
In the high absorption region, absorption coefficient, α(λ), is related to the energy of incident photons, hν, by band-to-band transition relation according to the Tauc34 procedure αhν = B(hν − Eg )n
(1)
where B is a constant nearly equal to one at absorption edge, and n is an index that characterizes the optical absorption process being theoretically equal to 0.5, 1.5, 2, or 3 for direct allowed, direct forbidden, indirect allowed, and indirect forbidden transitions, respectively.35 Figure 2 illustrates (αhv)2 versus (hv) for the CdSe colloidal nanocrystals. The optical direct band gap energy (Enano g ) of the
Figure 2. The variation of (αhν)2 versus photon energy (hv) for colloidal nanocrystalline CdSe.
nanocrystalline CdSe sol was also calculated from (αhv)2 plot as a function of photon energy (hv), and then the linear portion of the curve was extrapolated to a value of zero. The obtained value of the band gap for CdSe sol (Enano g ) is equal to 2.27 eV which is in good agreement with other published letters. The radiuses (R) of spherical nanoparticles Quantum Dots (QDs) were calculated by the effective mass approximation (eq 2).On the basis of peak of the absorption spectrum, the size of nanoparticles can be estimated by
3. RESULTS AND DISCUSSION 3.1. UV−vis. Figure 1 shows the visible absorption spectrum of the CdSe sol at room temperature which exhibited the
Egnano = Egbulk +
ℏ2π 2 e2 + A 4πεε0R 2μR2
(Enano g )
(2)
(Ebulk g ),
where is the energy band of the nanoparticle, is the energy band of the bulk, μ is the reduced mass, ℏ is Planck’s constant, ε is the dielectric constant with the value of 6.2,36 and ε0 is the permittivity constant which is equal to 8.854 × 10−12 C2 N−1 m−2. Factor A can be determined according to each transition (Figure 3). For the transition 1Sh → 1Se, it has a value of 1.786, and for the others it varies between 1.6 and 1.9.37,38 By placing these values in eq 2, the radius of CdSe colloidal nanostructure was obtained to be equal to 2.5 nm. The linear refractive indexes (n) of CdSe QDs were calculated by eq 3:
Figure 1. Absorption spectrum of CdSe colloidal nanostructure.
maximum peak absorption at 480 nm wavelength. Also the absorption spectra included an absorption shoulder at 500 nm with an absorption edge at 550 nm (2.26 eV) for the CdSe colloidal nanostructure. So a blue-shift of 0.56 eV in energy relative to the bulk CdSe (Eg = 1.70 eV, λ = 730 nm at 300 K) was seen,6 which is probably due to the quantum size effect as expected from the nanosized nature of the CdSe colloidal nanostructure.32,33
n=
1+
(εbulk − 1) 1 + (3/4D)1.2
(3)
Here εbulk = 6.2, and D is the average diameter of CdSe QDs in nm.10,39,40 The obtained result for linear refractive index of CdSe with D = 3 nm was 2.24. This technique is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the 7599
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3.4. XRD. In order to evaluate the crystalline phase, the CdSe colloidal sol was dried at room temperature. Figure 6
Figure 3. Energy bands of CdSe.
Figure 6. XRD pattern of CdSe nanopowder.
excited state to the ground state, while absorption measures transitions from the ground state to the excited state.41 3.2. TEM. Figure 4 shows the High Resolution TEM image and particle size distribution of the synthesized CdSe. Images
shows the X-ray diffraction (XRD) pattern of the CdSe nanopowder, which confirms that the crystalline phase of dried sol is cubic.43,44 The diffraction peaks of CdSe correspond to the diffraction of planes of (111), (220), (311), (400), (331), and (422). However, compared with the standard data, the intensity of the (111) diffraction peak is particularly strong relative to the other peaks, suggesting that the CdSe nanopowder grows along the (111) direction.45 The crystallite size of the particles has been calculated from the Debye− Scherrer’s formula using the X-ray line broadening by applying full width-half-maximum of highest intensity peak as follows46 s=
kλ B cos θ
(4)
where λ is the wavelength of the X-ray radiation (λ = 0.15406 nm), s is the crystallite size, k is a constant taken as 0.94, θ is the diffraction angle, and B is the full width of diffraction peak at half-maximum intensity. The average crystallite size of CdSe was calculated to be about 3 nm, in good agreement with the TEM result. 3.5. Photoluminescence. In Figure 7, the photoluminescence emission spectra of fresh and aged CdSe colloidal sol between 465 to 765 nm wavelengths are observed. Strong green emission was observed when the samples were excited at 440 nm wavelength. After two months no considerable changes in
Figure 4. (a) HR-TEM image of CdSe nanostructure and (b) the corresponding particle size distribution of CdSe.
indicate that the CdSe QDs had an average diameter approximately 3 nm size. The HR-TEM analysis also confirms the nanocrystallinity of the synthesized CdSe colloidal nanostructure. 3.3. FTIR. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the main organic compound bands related to vibration modes of prepared sol. CdSe colloidal nanocrystals FTIR spectra show the existence of cadmium selenide compound and long alkane chains solvents. In Figure 5 CH3
Figure 5. FTIR spectrum of the prepared sol.
bending deformed behavior can be observed at 1377 cm−1 and CH2 bending band behavior at 1463 cm−1. Also the transmittance peaks between 2850 and 3100 cm−1 wavenumber are due to the C−H and the C−O bonds. The Cd−Se band stretching can be observed at 712 cm−1.16,42 In this study, it is also observed that almost all existing peaks in FTIR spectra show a slightly shifting behavior toward a larger wavenumber as the crystal size increases.
Figure 7. PL spectra of the CdSe colloidal nanocrystal at excitation wavelength 440 nm. 7600
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Figure 8. PL emission intensity of the CdSe QDs as a function of the pH (a), concentration (b), and temperature (c).
and 100 °C during a heating cycle are shown in Figure 8c. As can be clearly seen, the PL emission intensity of the CdSe QDs decreased with increasing temperature.31,54
the intensity of photoluminescence spectrum was observed. These results are in agreement with the UV−Vis data in Figure 1. The green emission of CdSe nanocrystals is strongly dependent on size and shape.15 The photoluminescence quantum yield (QY) of CdSe sol was calculated using eq 5 by comparison with Fluorescein (Sigma-Aldrich) in 0.1 M aqueous NaOH taking its quantum yield as 95%:47 QY = QY r
I ODr n2 Ir OD nr2
4. CONCLUSION In summary, a green route sol−gel has been developed for the synthesis of colloidal CdSe nanocrystals by an improved method with 3 nm diameter. Several analytical techniques such as optical absorption spectroscopy, PL, FT-IR, XRD, and TEM were used to characterize the prepared CdSe sol. Experimental results confirm that the prepared CdSe colloidal nanocrystals have extra high luminescence green emission as compared to other published materials. FTIR analysis of CdSe colloidal nanocrystals was performed in order to investigate the synthesized products. X-ray diffraction results show the formation of a cubic cadmium selenide structure with a high degree of crystallinity. Upon aging at room temperature, there are no considerable changes in the intensity of photoluminescence spectrum of CdSe sol. This sol has enough potential to be used in preparation of nanostructured thin films, which are useful for optoelectronic applications. This future work is being pursued in our laboratory.
(5)
Here, I is the integrated intensity, OD is the optical density, and n is the refractive index.48,49 The subscript r refers to the Fluorescein with known quantum yield. We can calculate Optical Density (OD) of the CdSe nanocrystals, by using the Beer−Lambert Law47 A = log
I0 = OD I
(6)
where A is the absorbance, I is the light intensity at the center of the cuvette, and I0 is the intensity of the incident light to the cuvette. Beer’s Law predicts that the concentration of the absorbing species is directly proportional to the OD. So the PL emission intensity has also decreased with decreasing CdSe concentration. PL spectroscopy showed that quantum yield at (Cd:Se = 0.7:1.2) precursor molar ratio is 50.2% with 440 nm excitation wavelength, which is in agreement and better than reports in refs 15 and 50. The pH value played a serious role in growth of colloidal nanocrystals.51 The PL emission intensity of the obtained CdSe QDs at different pH values is displayed in Figure 8a, which demonstrates clearly that with the decrease of the pH value from 12.0 to 10.0, the PL intensity gradually decreased. Meantime, higher pH values helped nanoparticles to disperse better; these effects would provide better surface protection for the CdSe QDs and make them emit photons more efficiently with less nonradiative loss.52 As a result, we believed that higher pH values during the synthesis could help to improve the PL intensity of the CdSe QDs. Figure 8b shows the PL emission intensity of the CdSe QDs as a function of the concentration of distilled water used in the initial reaction, which shows obviously that when the concentration of water is systematically increased, the intensity of PL is decreased, which is in good agreement with other published letters.10,15 Up to now, examinations of the temperature-dependent PL properties of CdSe QDs have focused on single particles.53 PL emission spectra of the CdSe solution recorded at 25, 55, 75,
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AUTHOR INFORMATION
Corresponding Author
*Phone: +98-91-94520107. E-mail:
[email protected]; dr.gaeeni@ yahoo.com. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We gratefully acknowledge Tehran University of Medical Sciences (TUMS) for the financial support of this work. We also would like to thank Dr. M. Sasani Ghamsari and Dr. Amir Khalili for their help during various stages of this research.
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REFERENCES
(1) Tessler, N.; Medvedev, V.; Kazes, M.; Kan, S.; Banin, U. Efficient near-infrared polymer nanocrystal light-emitting diodes. Science 2002, 295, 1506−1508. (2) Huynh, W. U.; Dittmer, J. J.; Alivisatos, A. P. Hybrid nanorodpolymer solar cells. Science 2002, 295, 2425−2427. (3) Klein, D. L.; Roth, R.; Lim, A. K.; Alivisatos, A. P.; McEuen, P. L. A single-electron transistor made from a cadmium selenide nanocrystal. Nature 1997, 389, 699−701. (4) Kazes, M.; Lewis, D. Y.; Ebenstein, Y.; Mokari, T.; Banin, U. Lasing from semiconductor quantum rods in a cylindrical microcavity. Adv. Mater. 2002, 14, 317.
7601
dx.doi.org/10.1021/ie5004398 | Ind. Eng. Chem. Res. 2014, 53, 7598−7603
Industrial & Engineering Chemistry Research
Article
(26) Murphy, C. J. Sustainability as an emerging design criterion in nanoparticle synthesis and applications. J. Mater. Chem. 2008, 18, 2173−2176. (27) Dahl, J. A.; Maddux, B. L.; Hutchison, J. E. Toward greener nanosynthesis. Chem. Rev. 2007, 107, 2228−2269. (28) Oluwafemi, S.; Revaprasadu, N.; Ramirez, A. A novel one-pot route for the synthesis of water-soluble cadmium selenide nanoparticles. J. Cryst. Growth 2008, 310, 3230−3234. (29) Mulvihill, M. J.; Habas, S. E.; Jen-La Plante, I.; Wan, J.; Mokari, T. Influence of size, shape, and surface coating on the stability of aqueous suspensions of CdSe nanoparticles. Chem. Mater. 2010, 22, 5251−5257. (30) Arachchige, I. U.; Brock, S. L. Sol-gel assembly of CdSe nanoparticles to form porous aerogel networks. J. Am. Chem. Soc. 2006, 128, 7964−7971. (31) Joo, J.; Son, J. S.; Kwon, S. G.; Yu, J. H.; Hyeon, T. Lowtemperature solution-phase synthesis of quantum well structured CdSe nanoribbons. J. Am. Chem. Soc. 2006, 128, 5632−5633. (32) Oluwafemi, O. S. A novel “green” synthesis of starch-capped CdSe nanostructures. Colloids Surf., B 2009, 73, 382−386. (33) Wang, Z.; Lu, Q.; Kong, M.; Zhang, L. Manipulation of the Morphology of Semiconductor-Based Nanostructures from Core− Shell Nanoparticles to Nanocables: The Case of CdSe/SiO2. Chem. − Eur. J. 2007, 13, 1463−1470. (34) Tauc, J.; Grigorovici, R.; Vancu, A. Optical properties and electronic structure of amorphous germanium. Phys. Status Solidi B 1966, 15, 627−637. (35) Sreemany, M.; Sen, S. A simple spectrophotometric method for determination of the optical constants and band gap energy of multiple layer TiO2 thin films. Mater. Chem. Phys. 2004, 83, 169−177. (36) Wang, L.-W.; Zunger, A. Pseudopotential calculations of nanoscale CdSe quantum dots. Phys. Rev. B 1996, 53, 9579. (37) Peyghambarian, N.; Koch, S. W.; Mysyrowicz, A. Introduction to semiconductor optics. Prentice-Hall, Inc.: 1994. (38) Lippens, P.; Lannoo, M. Optical properties of II-VI semiconductor nanocrystals. Semicond. Sci. Technol. 1991, 6, A157. (39) Seo, J.; Ma, S.; Yang, Q.; Creekmore, L.; Battle, R.; Brown, H.; Jackson, A.; Skyles, T.; Tabibi, B.; Yu, W. In Large resonant third-order optical nonlinearity of CdSe nanocrystal quantum dots, J. Phys.: Conference Series, 2006; IOP Publishing: 2006; p 91. (40) Gerdova, I.; Haché, A. Third-order non-linear spectroscopy of CdSe and CdSe/ZnS core shell quantum dots. Opt. Commun. 2005, 246, 205−212. (41) Holler, F.; Skoog, D.; Crouch, S. Principles of instrumental analysis. Thomson: Belmont, 2007; pp 169−173. (42) Hamizi, N. A.; Ying, C. n. S.; Johan, M. R. Synthesis with Different Se Concentrations and Optical Studies of CdSe Quantum Dots via Inverse Micelle Technique. Int. J. Electrochem. Sci. 2012, 7, 4727−4734. (43) Kale, R.; Lokhande, C. Band gap shift, structural characterization and phase transformation of CdSe thin films from nanocrystalline cubic to nanorod hexagonal on air annealing. Semicond. Sci. Technol. 2005, 20, 1. (44) Hankare, P.; Bhuse, V.; Garadkar, K.; Delekar, S.; Mulla, I. Chemical deposition of cubic CdSe and HgSe thin films and their characterization. Semicond. Sci. Technol. 2004, 19, 70. (45) Wang, Z.; Lu, Q.; Fang, X.; Tian, X.; Zhang, L. Manipulation of the morphology of CdSe nanostructures: the effect of Si. Adv. Funct. Mater. 2006, 16, 661−666. (46) Ghamsari, M. S.; Mahzar, Z. A. S.; Radiman, S.; Hamid, A. M. A.; Khalilabad, S. R. Facile route for preparation of highly crystalline γAl2O3 nanopowder. Mater. Lett. 2012, 72, 32−35. (47) Lakowicz, J. R. Principles of fluorescence spectroscopy. Springer: 2009; pp 54−59. (48) Pacifici, D.; Lezec, H. J.; Atwater, H. A. All-optical modulation by plasmonic excitation of CdSe quantum dots. Nat. Photonics 2007, 1, 402−406.
(5) Pileni, M.-P. The role of soft colloidal templates in controlling the size and shape of inorganic nanocrystals. Nat. Mater. 2003, 2, 145− 150. (6) Klimov, V. I. Nanocrystal quantum dots-From fundamental photophysics to multicolor lasing. Los Alamos Sci. 2003, 28, 214−220. (7) Costa-Fernández, J. M.; Pereiro, R.; Sanz-Medel, A. The use of luminescent quantum dots for optical sensing. TrAC, Trends Anal. Chem. 2006, 25, 207−218. (8) Huang, X.; Zhang, X.; Zhu, Y.; Li, T.; Han, L.; Shang, X.; Ni, H.; Niu, Z. The effect of an electric field on the nonlinear response of InAs/GaAs quantum dots. J. Opt. 2010, 12, 055203. (9) Anikeeva, P. O.; Halpert, J. E.; Bawendi, M. G.; Bulovic, V. Quantum dot light-emitting devices with electroluminescence tunable over the entire visible spectrum. Nano Lett. 2009, 9, 2532−2536. (10) Talapin, D. V.; Rogach, A. L.; Kornowski, A.; Haase, M.; Weller, H. Highly luminescent monodisperse CdSe and CdSe/ZnS nanocrystals synthesized in a hexadecylamine-trioctylphosphine oxidetrioctylphospine mixture. Nano Lett. 2001, 1, 207−211. (11) Gao, X.; Cui, Y.; Levenson, R. M.; Chung, L. W.; Nie, S. In vivo cancer targeting and imaging with semiconductor quantum dots. Nat. Biotechnol. 2004, 22, 969−976. (12) Kang, S. H.; Huh, H. H.; Son, K. C.; Lee, C. S.; Kim, K. H.; Huh, C.; Kim, E. T. Light-emitting diode applications of colloidal CdSe/ZnS quantum dots embedded in TiO2−δ thin film. Phys. Status Solidi B 2009, 246, 889−892. (13) Greenham, N. C.; Peng, X.; Alivisatos, A. P. Charge separation and transport in conjugated-polymer/semiconductor-nanocrystal composites studied by photoluminescence quenching and photoconductivity. Phys. Rev. B 1996, 54, 17628. (14) Sholin, V.; Breeze, A.; Anderson, I.; Sahoo, Y.; Reddy, D.; Carter, S. All-inorganic CdSe/PbSe nanoparticle solar cells. Sol. Energy Mater. Sol. Cells 2008, 92, 1706−1711. (15) Qu, L.; Peng, X. Control of photoluminescence properties of CdSe nanocrystals in growth. J. Am. Chem. Soc. 2002, 124, 2049−2055. (16) Hamizi, N. A.; Johan, M. R. Synthesis and size dependent optical studies in CdSe quantum dots via inverse micelle technique. Mater. Chem. Phys. 2010, 124, 395−398. (17) Livingstone, R.; Zhou, X.; Tamargo, M. C.; Lombardi, J. R.; Quagliano, L. G.; Jean-Mary, F. Surface Enhanced Raman Spectroscopy of Pyridine on CdSe/ZnBeSe Quantum Dots Grown by Molecular Beam Epitaxy. J. Phys. Chem. C 2010, 114, 17460−17464. (18) Afzaal, M.; Aucott, S. M.; Crouch, D.; O’Brien, P.; Woollins, J. D.; Park, J. H. Deposition of MSe (M = Cd, Zn) Films by LPMOCVD from Novel Single-Source Precursors M [(SePPh2) 2N]2. Chem. Vap. Deposition 2002, 8, 187−189. (19) Xi, L.; Lam, Y. M.; Xu, Y. P.; Li, L.-J. Synthesis and characterization of one-dimensional CdSe by a novel reverse micelle assisted hydrothermal method. J. Colloid Interface Sci. 2008, 320, 491− 500. (20) Yao, W.-T.; Yu, S.-H.; Liu, S.-J.; Chen, J.-P.; Liu, X.-M.; Li, F.-Q. Architectural control syntheses of CdS and CdSe nanoflowers, branched nanowires, and nanotrees via a solvothermal approach in a mixed solution and their photocatalytic property. J. Phys. Chem. B 2006, 110, 11704−11710. (21) Nogami, M.; Suzuki, S.; Nagasaka, K. Sol-gel processing of small-sized CdSe crystal-doped silica glasses. J. Non-Cryst. Solids 1991, 135, 182−188. (22) Hench, L. L.; West, J. K. The sol-gel process. Chem. Rev. 1990, 90, 33−72. (23) Brinker, C. J.; Scherer, G. W. Sol-gel science: the physics and chemistry of sol-gel processing. Gulf Professional Publishing: 1990. (24) Mackenzie, J. D.; Bescher, E. P. Chemical Routes in the Synthesis of Nanomaterials Using the Sol−Gel Process. Acc. Chem. Res. 2007, 40, 810−818. (25) Arachchige, I. U.; Brock, S. L. Sol−Gel Methods for the Assembly of Metal Chalcogenide Quantum Dots. Acc. Chem. Res. 2007, 40, 801−809. 7602
dx.doi.org/10.1021/ie5004398 | Ind. Eng. Chem. Res. 2014, 53, 7598−7603
Industrial & Engineering Chemistry Research
Article
(49) Giblin, J.; Kuno, M. Nanostructure Absorption: A Comparative Study of Nanowire and Colloidal Quantum Dot Absorption Cross Sections. J. Phys. Chem. Lett. 2010, 1, 3340−3348. (50) Chen, O.; Zhao, J.; Chauhan, V. P.; Cui, J.; Wong, C.; Harris, D. K.; Wei, H.; Han, H.-S.; Fukumura, D.; Jain, R. K. Compact highquality CdSe−CdS core−shell nanocrystals with narrow emission linewidths and suppressed blinking. Nat. Mater. 2013, 12, 445−451. (51) Hiramatsu, H.; Osterloh, F. E. pH-controlled assembly and disassembly of electrostatically linked CdSe-SiO2 and Au-SiO2 nanoparticle clusters. Langmuir 2003, 19, 7003−7011. (52) Mahmoud, W. E.; Yaghmour, S. Synthesis, characterization and luminescence properties of thiol-capped CdSe quantum dots at different processing conditions. Opt. Mater. 2013, 35, 652−656. (53) Walker, G. W.; Sundar, V. C.; Rudzinski, C. M.; Wun, A. W.; Bawendi, M. G.; Nocera, D. G. Quantum-dot optical temperature probes. Appl. Phys. Lett. 2003, 83, 3555−3557. (54) Biju, V.; Makita, Y.; Sonoda, A.; Yokoyama, H.; Baba, Y.; Ishikawa, M. Temperature-sensitive photoluminescence of CdSe quantum dot clusters. J. Phys. Chem. B 2005, 109, 13899−13905.
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