- Email: [email protected]
Enhancement of CdSe quantum dots luminescence by calcium ions
Journal of Luminescence 134 (2013) 429–431
Contents lists available at SciVerse ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Enhancement of CdSe quantum dots luminescence by calcium ions Waleed E. Mahmoud n, S.J. Yaghmour, Amal M. Al-Amri Physics Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
a r t i c l e i n f o
abstract
Article history: Received 18 May 2012 Received in revised form 27 July 2012 Accepted 2 August 2012 Available online 13 August 2012
Water soluble functionalized CdSe quantum dots (QDs) have been prepared via water based route technique by using safe and low cost materials at low temperature 75 1C. The XRD measurements of the functionalized CdSe quantum dots showed that these quantum dots have a cubic phase with zinc blend structure. The TEM measurements depicted that these quantum dots are mono-dispersed with spherical shape size about 4 nm. The HRTEM measurements confirmed that the prepared quantum dots have single crystalline cubic structure with lattice parameter 0.61 nm. The EDX measurements indicated that the prepared quantum dots are highly pure and there are no impurities in the structures. The influence of calcium metal ions on the FL intensity of the functionalized CdSe QDs was enhanced the FL intensity by 5-times at concentration 0.8 mM. The enhancement effect of Ca2 þ ion on the fluorescence emission of CdSe QDs is found to be concentration dependence. & 2012 Elsevier B.V. All rights reserved.
Keywords: Semiconductor Crystal structure X-ray diffraction Luminescence
1. Introduction Nanotechnology has been heralded as a new field that has the potential to revolutionize medicine, as well as many other seemingly unrelated subjects, such as electronics, textiles and energy production [1,2]. The heart of this field lies in the ability to shrink the size of tools and devices to the nanometer range, and to assemble atoms and molecules into larger structures with useful properties, while maintaining their dimensions on the nanometer-length scale [3–5]. The nanometer scale is also the scale of biological function. Many nanotechnologies are predicted to soon become translational tools for medicine, and move quickly from discovery-based devices to clinically useful therapies and medical tests [6,7]. Among these, quantum dots (QDs) are unique in their far-reaching possibilities in many avenues of medicine. A QD is a fluorescent nanoparticle that has the potential to be used for medical imaging and tumors detection [8–10]. These particles have the unique ability to be sensitively detected on a wide range of length scales, from macroscale visualization, down to atomic resolution using electron microscopy [11,12]. In the present study, we aimed to get highly fluorescent CdSe QDs by novel strategy that has the potential to be used as a label for tissue biopsies and as a high resolution contrast agent for medical imaging for detection of smallest tumors.
(0.2 mol). Then aqueous solution was prepared by dissolving 0.0571 g cadmium chloride and 0.4883 g of 2-mercaptoethanol into 250 ml deionized water into three-neck flask; afterwards, the mixture was bubbled with N2 for 30 min. For the growth of the CdSe QDs, the solution of Na2SeSO3 was swiftly injected into the Cadmium-2-mercaptoethanol solution with constant stirring. After the injection of Na2SeSO3 solution, the temperature was increased to 75 1C. The reaction is refluxed under nitrogen gas for 30 min. The resulted CdSe QDs were separated and purified by centrifugation. The X-ray measurements were performed using Philips X’pert ˚ diffractometer supplied with copper X-ray tube (lka1 ¼1.5406 A). The working conditions were 40 kV and 30 mA for the X-ray tube, scan speed 0.051 and 2 s measuring time per step. High resolution transmission electron microscopy (HR-TEM) of CdSe nanocrystallites was carried out using a JEOL 2010 high-resolution transmission electron micro- scope operated at 200 kV. The photoluminescence was measured at room temperature by He–Cd laser with a wavelength 365 nm as the excitation source. This measurement was carried out by preparing a dilute solution of CdSe nanocrystallites in chloroform.
3. Results and discussion 2. Experimental Sodium selenosulfate (Na2SeSO3) solution was firstly prepared by dissolving Se (0.02 mmol) powder in 3 ml Na2SO3 solution n Corresponding author. Permanent address: Physics Department, Faculty of Science, Suez Canal University, Ismailia, Egypt. Tel.: þ966 560 860 583. E-mail address: [email protected] (W.E. Mahmoud).
0022-2313/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2012.08.007
The X-ray diffraction patterns were carried out for the prepared ME-capped CdSe samples and typical diffractogram is shown in Fig. 1. This figure declares that the as-synthesized sample has characteristic features matching the bulk cubic CdSe pattern. These diffraction patterns appear at about 25.21, 41.91, and 49.71 correspond to the (1 1 1), (2 2 0), and (3 1 1) Planes of metastable cubic CdSe with the lattice constant, a¼0.609 nm [JCPDS No. 19-0191]. No evidence was found for the existence of impurities in the quantum dot product.
430
W.E. Mahmoud et al. / Journal of Luminescence 134 (2013) 429–431
Fig. 1. XRD patterns for ME-capped CdSe QDs prepared at temperatures 75 1C.
Fig. 3. Effect of metal ions on fluorescence intensity of 2-mercaptoetanol-capped CdSe QDs, the concentration of 2-mercaptoetanol-capped CdSe QDs: 1.2 mg L 1 and concentration of metal ions: 0.2 mM at pH 9.0.
measurement for ME-capped CdSe nanoparticles. It is clear that, there are two peaks for carbon and oxygen in addition to Cd and Se atoms. The peaks of ‘‘C’’ and ‘‘O’’ are corresponding to mercaptoethanol capping agent, which confirms the covering of CdSe QDs with mercaptoethanol. The EDX measurement showed that the atomic ratio of Cd:Se is 0.55:0.45. Fig. 3 shows the influence of some metal ions, at fixed concentration (0.2 mM), on the FL intensity of 2-mercaptoethanol capped CdSe QDs. It is clear that, Ni2þ , Co2 þ , Pb2 þ , Zn2þ and Cd2þ ions do not show any effect on the FL intensity of the 2-mercaptoethanol capped CdSe QDs. Na þ , K þ , and Mg2 þ ions show relatively slight increase of the FL intensity of 2-mercaptoethanol capped CdSe QDs. As compared with Ca2þ ion solutions, the influence of Ca2 þ metal ion is very high, where the Ca2þ ions enhanced the FL intensity 3-times. The effect of Ca2þ ions on the fluorescence emission of the 2-mercaptoethanol capped CdSe QDs is shown in Fig. 4a. The fluorescence intensity is significantly enhanced by the addition of Ca2 þ ion. The enhancement effect of Ca2 þ ion on the fluorescence emission of CdSe QDs is found to be concentration dependence. The enhancement of fluorescence intensity of 2-mercaptoethanol capped CdSe QDs is well linearly proportional to the Ca2 þ ion concentration along the range from 1.0 10 7 to 8.0 10 7 mol L 1 as indicated in Fig. 4b. Therefore, this ensemble can be used for the development of a sensitive and selective method for Ca2 þ ion sensor. The possible mechanism for enhancing the FL intensity of CdSe quantum dots may be attributed to the formation of a calcium–mercaptoethanol complex on the surface of the CdSe QDs. This reaction mechanism results in formation of calcium oxide on the surface of CdSe QDs. This calcium oxide is good matrix for hosting luminescence materials. Therefore enhance the transition energy transfer which gives rise to the increase of population of inversion symmetry of the QDs [13–15]. Fig. 2. (a) TEM image (inset HRTEM image) and (b) EDX measurement for ME-capped CdSe QDs prepared at temperatures 75 1C.
Fig. 2a shows the typical TEM image of the as-synthesized ME-capped CdSe NCs at reaction temperature 75 1C. The TEM measurement showed that the size distribution of the nanoparticles was nearly monodisperse. The average size of ME-capped CdSe nanoparticles is 4.0270.07 nm. The existence of lattice planes on the HRTEM (inset of Fig. 2a) confirmed the good crystallinity of the CdSe NCs. It is also indexed to the cubic phase of CdSe with lattice constant a¼0.61 nm. Fig. 2b depicts the EDX
4. Conclusion 2-mercaptoethanol capped CdSe quantum dots have been synthesized via low cost and friendly materials. The XRD depicted that these quantum dots have cubic structure. The TEM image showed that the synthesized quantum dots have average particle size 4 nm. The EDX measurement indicated that the atomic ratio of Cd:Se is 0.55: 0.45. The influence of some selected metal ions on the FL intensity of 2-mercaptoethanol capped CdSe QDs depicted that, Ni2 þ , Co2 þ , Pb2 þ , Zn2 þ and Cd2 þ ions do not
W.E. Mahmoud et al. / Journal of Luminescence 134 (2013) 429–431
431
Fig. 4. Influence of calcium ions concentration on the fluorescence intensity of the 2-mercaptoethanol capped CdSe quantum dots.
show any effect on the FL intensity of the CdSe QDs while Ca2 þ metal ion has very high effect, where the Ca2 þ ions enhanced the FL intensity by 3-times at 0.2 mM. The enhancement of fluorescence intensity of the functionalized CdSe QDs is well linearly proportional to the Ca2 þ ion concentration along the range from 1.0 10 7 to 8.0 10 7 mol L 1. The increase of FL intensity may be attributed to the formation of a calcium–mercaptoethanol complex on the surface of the CdSe QDs, which results in a restriction of the 2-mercaptoethanol rotation and in turn effective core protection. References [1] Z.A. Peng, X.G. Peng, J. Am. Chem. Soc. 123 (2001) 183.
[2] W.E. Mahmoud, T. Al-Harbi, J. Cryst. Growth 327 (1) (2011) 52. [3] W.E. Mahmoud, J. Cryst. Growth 312 (21) (2010) 3075. [4] W.E. Mahmoud, A.A. Al-Ghamdi, S. Al-Heniti, S. Al-Ameer, J. Alloys Compd. 491 (1-2) (2010) 742. [5] R. Al-Tuwirqi, A.A. Al-Ghamdi, N.A. Aal, A. Umar, W.E. Mahmoud, Superlattices Microstruct. 49 (4) (2011) 416. [6] R.K. Jain, M. Stroh, Nat. Biotechnol. 22 (8) (2004) 959. [7] Y. Yin, A.P. Alivisatos, Nature 437 (2005) 664. [8] A. Smith, X.H. Gao, S. Nie, Photochem. Photobiol. 80 (2004) 377. [9] M. Bruchez, M. Moronne, P. Gin, S. Weiss, A.P. Alivisatos, Science 281 (5385) (1998) 2013. [10] W.E. Mahmoud, S.J. Yaghmour, Luminescence 132 (2012) 2447. [11] W.E. Mahmoud, A.A. Al-Ghamdi, Opt. Laser Technol. 42 (7) (2010) 1134. [12] A.M. Al-Amri, S.J. Yaghmour, W.E. Mahmoud, Cryst. Growth 334 (2011) 76. [13] W.E. Mahmoud, A.M. Al-Amri, S.J. Yaghmour, Opt. Mater. 34 (7) (2012) 1082. [14] W.E. Mahmoud, Sensors Actuators B 164 (1) (2012) 76. [15] R. Freeman, I. Willner, Chem. Soc. Rev. 41 (2012) 4067.
Contents lists available at SciVerse ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Enhancement of CdSe quantum dots luminescence by calcium ions Waleed E. Mahmoud n, S.J. Yaghmour, Amal M. Al-Amri Physics Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
a r t i c l e i n f o
abstract
Article history: Received 18 May 2012 Received in revised form 27 July 2012 Accepted 2 August 2012 Available online 13 August 2012
Water soluble functionalized CdSe quantum dots (QDs) have been prepared via water based route technique by using safe and low cost materials at low temperature 75 1C. The XRD measurements of the functionalized CdSe quantum dots showed that these quantum dots have a cubic phase with zinc blend structure. The TEM measurements depicted that these quantum dots are mono-dispersed with spherical shape size about 4 nm. The HRTEM measurements confirmed that the prepared quantum dots have single crystalline cubic structure with lattice parameter 0.61 nm. The EDX measurements indicated that the prepared quantum dots are highly pure and there are no impurities in the structures. The influence of calcium metal ions on the FL intensity of the functionalized CdSe QDs was enhanced the FL intensity by 5-times at concentration 0.8 mM. The enhancement effect of Ca2 þ ion on the fluorescence emission of CdSe QDs is found to be concentration dependence. & 2012 Elsevier B.V. All rights reserved.
Keywords: Semiconductor Crystal structure X-ray diffraction Luminescence
1. Introduction Nanotechnology has been heralded as a new field that has the potential to revolutionize medicine, as well as many other seemingly unrelated subjects, such as electronics, textiles and energy production [1,2]. The heart of this field lies in the ability to shrink the size of tools and devices to the nanometer range, and to assemble atoms and molecules into larger structures with useful properties, while maintaining their dimensions on the nanometer-length scale [3–5]. The nanometer scale is also the scale of biological function. Many nanotechnologies are predicted to soon become translational tools for medicine, and move quickly from discovery-based devices to clinically useful therapies and medical tests [6,7]. Among these, quantum dots (QDs) are unique in their far-reaching possibilities in many avenues of medicine. A QD is a fluorescent nanoparticle that has the potential to be used for medical imaging and tumors detection [8–10]. These particles have the unique ability to be sensitively detected on a wide range of length scales, from macroscale visualization, down to atomic resolution using electron microscopy [11,12]. In the present study, we aimed to get highly fluorescent CdSe QDs by novel strategy that has the potential to be used as a label for tissue biopsies and as a high resolution contrast agent for medical imaging for detection of smallest tumors.
(0.2 mol). Then aqueous solution was prepared by dissolving 0.0571 g cadmium chloride and 0.4883 g of 2-mercaptoethanol into 250 ml deionized water into three-neck flask; afterwards, the mixture was bubbled with N2 for 30 min. For the growth of the CdSe QDs, the solution of Na2SeSO3 was swiftly injected into the Cadmium-2-mercaptoethanol solution with constant stirring. After the injection of Na2SeSO3 solution, the temperature was increased to 75 1C. The reaction is refluxed under nitrogen gas for 30 min. The resulted CdSe QDs were separated and purified by centrifugation. The X-ray measurements were performed using Philips X’pert ˚ diffractometer supplied with copper X-ray tube (lka1 ¼1.5406 A). The working conditions were 40 kV and 30 mA for the X-ray tube, scan speed 0.051 and 2 s measuring time per step. High resolution transmission electron microscopy (HR-TEM) of CdSe nanocrystallites was carried out using a JEOL 2010 high-resolution transmission electron micro- scope operated at 200 kV. The photoluminescence was measured at room temperature by He–Cd laser with a wavelength 365 nm as the excitation source. This measurement was carried out by preparing a dilute solution of CdSe nanocrystallites in chloroform.
3. Results and discussion 2. Experimental Sodium selenosulfate (Na2SeSO3) solution was firstly prepared by dissolving Se (0.02 mmol) powder in 3 ml Na2SO3 solution n Corresponding author. Permanent address: Physics Department, Faculty of Science, Suez Canal University, Ismailia, Egypt. Tel.: þ966 560 860 583. E-mail address: [email protected] (W.E. Mahmoud).
0022-2313/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2012.08.007
The X-ray diffraction patterns were carried out for the prepared ME-capped CdSe samples and typical diffractogram is shown in Fig. 1. This figure declares that the as-synthesized sample has characteristic features matching the bulk cubic CdSe pattern. These diffraction patterns appear at about 25.21, 41.91, and 49.71 correspond to the (1 1 1), (2 2 0), and (3 1 1) Planes of metastable cubic CdSe with the lattice constant, a¼0.609 nm [JCPDS No. 19-0191]. No evidence was found for the existence of impurities in the quantum dot product.
430
W.E. Mahmoud et al. / Journal of Luminescence 134 (2013) 429–431
Fig. 1. XRD patterns for ME-capped CdSe QDs prepared at temperatures 75 1C.
Fig. 3. Effect of metal ions on fluorescence intensity of 2-mercaptoetanol-capped CdSe QDs, the concentration of 2-mercaptoetanol-capped CdSe QDs: 1.2 mg L 1 and concentration of metal ions: 0.2 mM at pH 9.0.
measurement for ME-capped CdSe nanoparticles. It is clear that, there are two peaks for carbon and oxygen in addition to Cd and Se atoms. The peaks of ‘‘C’’ and ‘‘O’’ are corresponding to mercaptoethanol capping agent, which confirms the covering of CdSe QDs with mercaptoethanol. The EDX measurement showed that the atomic ratio of Cd:Se is 0.55:0.45. Fig. 3 shows the influence of some metal ions, at fixed concentration (0.2 mM), on the FL intensity of 2-mercaptoethanol capped CdSe QDs. It is clear that, Ni2þ , Co2 þ , Pb2 þ , Zn2þ and Cd2þ ions do not show any effect on the FL intensity of the 2-mercaptoethanol capped CdSe QDs. Na þ , K þ , and Mg2 þ ions show relatively slight increase of the FL intensity of 2-mercaptoethanol capped CdSe QDs. As compared with Ca2þ ion solutions, the influence of Ca2 þ metal ion is very high, where the Ca2þ ions enhanced the FL intensity 3-times. The effect of Ca2þ ions on the fluorescence emission of the 2-mercaptoethanol capped CdSe QDs is shown in Fig. 4a. The fluorescence intensity is significantly enhanced by the addition of Ca2 þ ion. The enhancement effect of Ca2 þ ion on the fluorescence emission of CdSe QDs is found to be concentration dependence. The enhancement of fluorescence intensity of 2-mercaptoethanol capped CdSe QDs is well linearly proportional to the Ca2 þ ion concentration along the range from 1.0 10 7 to 8.0 10 7 mol L 1 as indicated in Fig. 4b. Therefore, this ensemble can be used for the development of a sensitive and selective method for Ca2 þ ion sensor. The possible mechanism for enhancing the FL intensity of CdSe quantum dots may be attributed to the formation of a calcium–mercaptoethanol complex on the surface of the CdSe QDs. This reaction mechanism results in formation of calcium oxide on the surface of CdSe QDs. This calcium oxide is good matrix for hosting luminescence materials. Therefore enhance the transition energy transfer which gives rise to the increase of population of inversion symmetry of the QDs [13–15]. Fig. 2. (a) TEM image (inset HRTEM image) and (b) EDX measurement for ME-capped CdSe QDs prepared at temperatures 75 1C.
Fig. 2a shows the typical TEM image of the as-synthesized ME-capped CdSe NCs at reaction temperature 75 1C. The TEM measurement showed that the size distribution of the nanoparticles was nearly monodisperse. The average size of ME-capped CdSe nanoparticles is 4.0270.07 nm. The existence of lattice planes on the HRTEM (inset of Fig. 2a) confirmed the good crystallinity of the CdSe NCs. It is also indexed to the cubic phase of CdSe with lattice constant a¼0.61 nm. Fig. 2b depicts the EDX
4. Conclusion 2-mercaptoethanol capped CdSe quantum dots have been synthesized via low cost and friendly materials. The XRD depicted that these quantum dots have cubic structure. The TEM image showed that the synthesized quantum dots have average particle size 4 nm. The EDX measurement indicated that the atomic ratio of Cd:Se is 0.55: 0.45. The influence of some selected metal ions on the FL intensity of 2-mercaptoethanol capped CdSe QDs depicted that, Ni2 þ , Co2 þ , Pb2 þ , Zn2 þ and Cd2 þ ions do not
W.E. Mahmoud et al. / Journal of Luminescence 134 (2013) 429–431
431
Fig. 4. Influence of calcium ions concentration on the fluorescence intensity of the 2-mercaptoethanol capped CdSe quantum dots.
show any effect on the FL intensity of the CdSe QDs while Ca2 þ metal ion has very high effect, where the Ca2 þ ions enhanced the FL intensity by 3-times at 0.2 mM. The enhancement of fluorescence intensity of the functionalized CdSe QDs is well linearly proportional to the Ca2 þ ion concentration along the range from 1.0 10 7 to 8.0 10 7 mol L 1. The increase of FL intensity may be attributed to the formation of a calcium–mercaptoethanol complex on the surface of the CdSe QDs, which results in a restriction of the 2-mercaptoethanol rotation and in turn effective core protection. References [1] Z.A. Peng, X.G. Peng, J. Am. Chem. Soc. 123 (2001) 183.
[2] W.E. Mahmoud, T. Al-Harbi, J. Cryst. Growth 327 (1) (2011) 52. [3] W.E. Mahmoud, J. Cryst. Growth 312 (21) (2010) 3075. [4] W.E. Mahmoud, A.A. Al-Ghamdi, S. Al-Heniti, S. Al-Ameer, J. Alloys Compd. 491 (1-2) (2010) 742. [5] R. Al-Tuwirqi, A.A. Al-Ghamdi, N.A. Aal, A. Umar, W.E. Mahmoud, Superlattices Microstruct. 49 (4) (2011) 416. [6] R.K. Jain, M. Stroh, Nat. Biotechnol. 22 (8) (2004) 959. [7] Y. Yin, A.P. Alivisatos, Nature 437 (2005) 664. [8] A. Smith, X.H. Gao, S. Nie, Photochem. Photobiol. 80 (2004) 377. [9] M. Bruchez, M. Moronne, P. Gin, S. Weiss, A.P. Alivisatos, Science 281 (5385) (1998) 2013. [10] W.E. Mahmoud, S.J. Yaghmour, Luminescence 132 (2012) 2447. [11] W.E. Mahmoud, A.A. Al-Ghamdi, Opt. Laser Technol. 42 (7) (2010) 1134. [12] A.M. Al-Amri, S.J. Yaghmour, W.E. Mahmoud, Cryst. Growth 334 (2011) 76. [13] W.E. Mahmoud, A.M. Al-Amri, S.J. Yaghmour, Opt. Mater. 34 (7) (2012) 1082. [14] W.E. Mahmoud, Sensors Actuators B 164 (1) (2012) 76. [15] R. Freeman, I. Willner, Chem. Soc. Rev. 41 (2012) 4067.