Photoluminescence enhancement in CdS quantum dots by thermal annealing
- Jae Ik Kim†1,
- Jongmin Kim†1,
- Junhee Lee†1,
- Dae-Ryong Jung1,
- Hoechang Kim1,
- Hongsik Choi1,
- Sungjun Lee1,
- Sujin Byun1,
- Suji Kang1 and
- Byungwoo Park1Email author
© Kim et al.; licensee Springer. 2012
Received: 12 July 2012
Accepted: 18 August 2012
Published: 29 August 2012
The photoluminescence behavior of CdS quantum dots in initial growth stage was studied in connection with an annealing process. Compared to the as-synthesized CdS quantum dots (quantum efficiency ≅ 1%), the heat-treated sample showed enhanced luminescence properties (quantum efficiency ≅ 29%) with a narrow band-edge emission. The simple annealing process diminished the accumulated defect states within the nanoparticles and thereby reduced the nonradiative recombination, which was confirmed by diffraction, absorption, and time-resolved photoluminescence. Consequently, the highly luminescent and defect-free nanoparticles were obtained by a facile and straightforward process.
Due to the benefits of their size-tunable physical properties [1–3], nanoscale semiconductor materials have promising future applications, including the optoelectronic devices such as light-emitting diodes [4–8] and next-generation quantum dot solar cells [9–14]. Moreover, nanoscale semiconductors functionalized with biomolecules are used as molecular fluorescent probes in biological applications .
In recent years, there has been a rapid development of the growth techniques for quantum dots with high crystallinity and narrow size distribution [16–18]. The hot-injection techniques allow the affordable growth of a wide range of nanoscale materials with high quality [19–21]. On the other hand, low-temperature synthesis has not been actively studied yet. Low-temperature synthesis has higher potential than hot-injection techniques because the process is relatively simple and nontoxic . However, the size distribution and the crystallinity of nanoparticles are generally poor because of low synthetic temperature and surface defects . Recently, several papers have introduced advanced low-temperature synthesis and colloidal growth that can yield quantum dots with a sufficiently narrow size distribution [24–27].
In this regard, introducing a facile annealing process has great potential for enhancing the quantum efficiency and tuning the size of nanocrystals. However, systematic analysis of the initial growth stage of the nanoparticles has rarely been studied. In this work, a simple aqueous system and straightforward annealing process were applied to the preparation of highly luminescent CdS quantum dots. The appropriate annealing condition was well correlated with the quantum dot size, local strain (crystallinity), and radiative/nonradiative recombination rates.
The CdS quantum dots were synthesized by using a combination of the reverse-micelle method and post-growth annealing process. Cadmium chloride (CdCl2, 0.182 g) and sodium sulfide (Na2S, 0.036 g) were separately dissolved in distilled water (15 ml) and stirred to achieve their complete dissolution. Linoleic acid ((C17H31)COOH, 2.4 ml) and sodium linoleate ((C17H31)COONa, 2 g) were dissolved in ethanol (15 ml) and formed transparent solutions. After the two solutions were mixed and stirred vigorously, the color changed from transparent to opaque white, implying the formation of a microemulsion consisting of cadmium linoleate. After the addition of sodium sulfide, the color changed from white to greenish yellow. For the annealing process, the autoclave was heated at 100°C for 1 to 24 h. In order to increase the quantum dot size, post-growth annealing was also conducted at 125°C to 225°C with the same annealing time (12 h). The resultant CdS quantum dots were precipitated by using centrifugation and cleaned several times with ethanol. Finally, the CdS quantum dots were dispersed into chloroform (CHCl3, 40 ml), displaying a translucent yellow solution.
The structural properties of the quantum dots, such as crystal size and local strain, were studied using X-ray diffraction (XRD; M18XHF-SRA, MAC Science, Yokohama, Japan) with θ to 2θ curves. To analyze the optical properties, the absorbance was measured using UV/visible spectrometry, and the photoluminescence (PL) data were measured under 360-nm excitation wavelength with a spectrofluorometer (FP-6500, JASCO, Essex, UK). The binding energy of CdS quantum dots was analyzed by X-ray photoelectron spectroscopy (XPS; Sigma Probe, Thermo VG Scientific, Logan, UT, USA) using Al Kα radiation (1,486.6 eV). Time-resolved PL was measured by using a picosecond laser system (FLS920P, Edinburgh Instruments Ltd., Livingston, UK), and the nanostructures of the CdS nanoparticles were analyzed by a high-resolution transmission electron microscopy (TEM; JEM-3000 F, JEOL Ltd., Tokyo, Japan).
Results and discussion
The luminescence properties of CdS quantum dots in the initial growth stage were examined in connection with a simple annealing process. Both the accumulated defect states and nonradiative recombination rates were reduced, and these correlations were confirmed systematically by diffraction, absorption, and time-resolved photoluminescence. Consequently, the highly luminescent (quantum efficiency of 29% from the initial 1%) and defect-free nanoparticles were obtained by a facile annealing process.
This research was supported by the National Research Foundation of Korea through the World Class University (WCU, R31-2008-000-10075-0) and the Korean government (MEST:NRF, 2010–0029065).
- Scholes GD, Rumbles G: Excitons in nanoscale systems. Nat Mater 2006, 5: 683–696. 10.1038/nmat1710View ArticleGoogle Scholar
- Kelly KL, Coronado E, Zhao LL, Schatz GC: The optical properties of metal nanoparticles: the influence of size, shape, and dielectric environment. J Phys Chem B 2003, 107: 668–677.View ArticleGoogle Scholar
- Trindade T, O’Brien P, Pickett NL: Nanocrystalline semiconductors: synthesis, properties, and perspectives. Chem Mater 2001, 13: 3843–3858. 10.1021/cm000843pView ArticleGoogle Scholar
- Wang X, Wang ZM, Liang B, Salamo GJ, Shih CK: Direct spectroscopic evidence for the formation of one-dimensional wetting wires during the growth of InGaAs/GaAs quantum dot chains. Nano Lett 2006, 6: 1847–1851. 10.1021/nl060271tView ArticleGoogle Scholar
- Schlamp MC, Peng X, Alivisatos AP: Improved efficiencies in light emitting diodes made with CdSe(CdS) core/shell type nanocrystals and a semiconducting polymer. J Appl Phys 1997, 82: 5837–5842. 10.1063/1.366452View ArticleGoogle Scholar
- Lee SM, Choi KC, Kim DH, Jeon DY: Localized surface plasmon enhanced cathodoluminescence from Eu3+-doped phosphor near the nanoscaled silver particles. Opt Express 2011, 19: 13209–13217. 10.1364/OE.19.013209View ArticleGoogle Scholar
- Wu J, Lee S, Reddy VR, Manasreh MO, Weaver BD, Yakes MK, Furrow CS, Kunets VP, Benamara M, Salamo GJ: Photoluminescence plasmonic enhancement in InAs quantum dots coupled to gold nanoparticles. Mat Lett 2011, 65: 3605–3608. 10.1016/j.matlet.2011.08.019View ArticleGoogle Scholar
- Li Z, Wu J, Wang ZM, Fan D, Guo A, Li S, Yu SQ, Manasreh O, Salamo GJ: InGaAs quantum well grown on high-index surfaces for superluminescent diode applications. Nanoscale Res Lett 2010, 5: 1079–1084. 10.1007/s11671-010-9605-2View ArticleGoogle Scholar
- Shen Y, Lee Y: Assembly of CdS quantum dots onto mesoscopic TiO2 films for quantum dot-sensitized solar cell applications. Nanotechnology 2008, 19: 045602. 10.1088/0957-4484/19/04/045602View ArticleGoogle Scholar
- Biswas S, Hossain MF, Takahashi T: Fabrication of Grtäzel solar cell with TiO2/CdS bilayered photoelectrode. Thin Solid Films 2008, 517: 1284–1288. 10.1016/j.tsf.2008.06.010View ArticleGoogle Scholar
- Kim J, Choi H, Nahm C, Moon J, Kim C, Nam S, Jung DR, Park B: The effect of a blocking layer on the photovoltaic performance in CdS quantum-dot-sensitized solar cells. J Power Sources 2011, 196: 10526–10531. 10.1016/j.jpowsour.2011.08.052View ArticleGoogle Scholar
- Tang L, Li X, Cammarata RC, Friesen C, Sieradzki K: Electrochemical stability of elemental metal nanoparticles. J Am Chem Soc 2010, 132: 11722–11726. 10.1021/ja104421tView ArticleGoogle Scholar
- Hu MS, Chen HL, Shen CH, Hong LS, Huang BR, Chen KH, Chen LC: Photosensitive gold-nanoparticle-embedded dielectric nanowires. Nat Mater 2006, 5: 102–106. 10.1038/nmat1564View ArticleGoogle Scholar
- Martí A, Antolín E, Stanley CR, Farmer CD, López N, Díaz P, Cánovas E, Linares PG, Luque A: Production of photocurrent due to intermediate-to-conduction-band transitions: a demonstration of a key operating principle of the intermediate-band solar cell. Phys Rev Lett 2006, 97: 247701.View ArticleGoogle Scholar
- Bruchez M, Morrone M, Gin P, Weiss S, Alivisatos AP: Semiconductor nanocrystals as fluorescent biological labels. Science 1998, 281: 2013–2016.View ArticleGoogle Scholar
- Laurent S, Forge D, Port M, Roch A, Robic C, Vander EL, Muller RN: Magnetic iron oxide nanoparticles: synthesis, stabilization, vectorization, physicochemical characterizations, and biological applications. Chem Rev 2008, 108: 2064–2110. 10.1021/cr068445eView ArticleGoogle Scholar
- Sau TK, Rogach AL: Nonspherical noble metal nanoparticles: colloid-chemical synthesis and morphology control. Adv Mater 2010, 22: 1781–1804. 10.1002/adma.200901271View ArticleGoogle Scholar
- Yang H, Luan W, Tu ST, Wang ZM: Synthesis of nanocrystals via microreaction with temperature gradient: towards separation of nucleation and growth. Lab Chip 2008, 8: 451–455. 10.1039/b715540aView ArticleGoogle Scholar
- Murray CB, Norris DJ, Bawendi MG: Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites. J Am Chem Soc 1993, 115: 8706–8715. 10.1021/ja00072a025View ArticleGoogle Scholar
- Peng X, Manna L, Yang W, Wickham J, Scher E, Kadavanich A, Alivisatos AP: Shape control of CdSe nanocrystals. Nature 2000, 404: 59–61. 10.1038/35003535View ArticleGoogle Scholar
- Hyeon T: Chemical synthesis of magnetic nanoparticles. Chem Comm 2003, 9: 927–934.View ArticleGoogle Scholar
- Zhao N, Qi L: Low-temperature synthesis of star-shaped PbS nanocrystals in aqueous solutions of mixed cationic/anionic surfactants. Adv Mater 2006, 18: 359–362. 10.1002/adma.200501756View ArticleGoogle Scholar
- Shi JW, Yan X, Cui HJ, Zong X, Fu ML, Chen S, Wang L: Low-temperature synthesis of CdS/TiO2 composite photocatalysts: influence of synthetic procedure on photocatalytic activity under visible light. J Mol Catal A 2012, 356: 53–60.View ArticleGoogle Scholar
- Wang X, Zhuang J, Peng Q, Li Y: A general strategy for nanocrystal synthesis. Nature 2005, 437: 121–124. 10.1038/nature03968View ArticleGoogle Scholar
- Kwon SG, Hyeon T: Formation mechanisms of uniform nanocrystals via hot-injection and heat-up methods. Small 2011, 7: 2685–2702. 10.1002/smll.201002022View ArticleGoogle Scholar
- Son D, Jung DR, Kim J, Moon T, Kim C, Park B: Synthesis and photoluminescence of Mn-doped zinc sulfide nanoparticles. Appl Phys Lett 2007, 90: 101910. 10.1063/1.2711709View ArticleGoogle Scholar
- Joo J, Na H, Yu T, Yu J, Kim Y, Xu F, Zhang J, Hyeon T: Generalized and facile synthesis of semiconducting metal sulfide nanocrystals. J Am Chem Soc 2003, 125: 11100–11105. 10.1021/ja0357902View ArticleGoogle Scholar
- Jung DR, Kim J, Park B: Surface-passivation effects on the photoluminescence enhancement in ZnS:Mn nanoparticles by ultraviolet irradiation with oxygen bubbling. Appl Phys Lett 2010, 96: 211908. 10.1063/1.3431267View ArticleGoogle Scholar
- Moon T, Hwang S, Jung D, Son D, Kim C, Kim J, Kang M, Park B: Hydroxyl-quenching effects on the photoluminescence properties of SnO2:Eu3+. J Phys Chem C 2007, 111: 4164–4167. 10.1021/jp067217lView ArticleGoogle Scholar
- Kim T, Oh J, Park B: Correlation between strain and dielectric properties in ZrTiO4 thin films. Appl Phys Lett 2000, 76: 3043–3045. 10.1063/1.126573View ArticleGoogle Scholar
- Warren BE: X-Ray Diffraction. Dover, New York; 1990:257–262.Google Scholar
- Rengaraj S, Venkataraj S, Jee S, Kim Y, Tai C, Repo E, Koistinen A, Ferancova A, Sillanpää M: Cauliflower-like CdS microspheres composed of nanocrystals and their physicochemical properties. Langmuir 2011, 27: 352–358. 10.1021/la1032288View ArticleGoogle Scholar
- Jin Z, Li Q, Xi C, Jian Z, Chen Z: Effect of high-temperature treatment in air ambience on the surface composition and structure of CdS. Appl Surf Sci 1988, 32: 218–232. 10.1016/0169-4332(88)90082-7View ArticleGoogle Scholar
- Kundu S, Wang Y, Xia W, Muhler M: Thermal stability and reducibility of oxygen-containing functional groups on multiwalled carbon nanotube surfaces: a quantitative high-resolution XPS and TPD/TPR study. J Phys Chem C 2008, 112: 16869–16878. 10.1021/jp804413aView ArticleGoogle Scholar
- Jang E, Jun S, Chung Y, Pu L: Surface treatment to enhance the quantum efficiency of semiconductor nanocrystals. J Phys Chem B 2004, 108: 4597–4600. 10.1021/jp049475tView ArticleGoogle Scholar
- Saunders AE, Ghezelbash A, Sood P, Korgel BA: Synthesis of high aspect ratio quantum-size CdS nanorods and their surface-dependent photoluminescence. Langmuir 2008, 24: 9043–9049. 10.1021/la800964sView ArticleGoogle Scholar
- Jones M, Nedeljkovic J, Ellingson RJ, Nozik AJ, Rumbles G: Photoenhancement of luminescence in colloidal CdSe quantum dot solutions. J Phys Chem B 2003, 107: 11346–11352. 10.1021/jp035598mView ArticleGoogle Scholar
- Wu J, Wang ZM, Dorogan VG, Li S, Mazur YI, Salamo GJ: Near infrared broadband emission of In0.35Ga0.65As quantum dots on high index GaAs surfaces. Nanoscale 2011, 3: 1485–1488. 10.1039/c0nr00973cView ArticleGoogle Scholar
- Na CW, Han DS, Kim DS, Kang YJ, Lee JY, Park J, Oh DK, Kim KS, Kim D: Photoluminescence of Cd1-xMnxS (x ≤ 0.3) nanowires. J Phys Chem B 2006, 110: 6699–6704. 10.1021/jp060224pView ArticleGoogle Scholar
- Sarma DD, Nag A, Santra PK, Kumar A, Sapra S, Mahadevan P: Origin of the enhanced photoluminescence from semiconductor CdSeS nanocrystals. J Phys Chem Lett 2010, 3: 2149–2153.View ArticleGoogle Scholar
- Jung DR, Son D, Kim J, Kim C, Park B: Highly luminescent surface-passivated ZnS:Mn nanoparticles by a simple one-step synthesis. Appl Phys Lett 2008, 93: 163118. 10.1063/1.3007980View ArticleGoogle Scholar
- Fischer M, Georges J: Fluorescence quantum yield of rhodamine 6 G in ethanol as a function of concentration using thermal lens spectrometry. Chem Phys Lett 1996, 260: 115–118. 10.1016/0009-2614(96)00838-XView ArticleGoogle Scholar
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