Synthesis of fluorescent CdSe quantum dots under mild chemical conditions H. N. Rathnaweera and T. G. Chasteen Department of Chemistry

Introduction Quantum Dots (QDs)  Quantum dots are extremely small particles made of semiconductor materials, usually ranging from 2-10 nanometers in diameter.  QDs were discovered in the early 1980s by Alexie Ekimov in a glass matrix and by Louis E. Brus in colloidal solutions. 2 (08/15/2014)

Solar cells Biosensors Light emitting diodes Flat-panel displays Photo detectors Lasers blog.light-innovations.com ( ) 3 CdSe Quantum Dots  CdSe QDs are used in a wide range of applications

 QDs display unique optical and electrical properties due to their size and composition. 4 (08/15/2014) Quantum dot color depends on its size  QDs have an ability to produce fluorescence.

 Over the past few years, there was a remarkable progress in synthesizing CdSe QDs using various methods.  These methods involve various organic solvents, high temperatures, high pressures and toxic substrates. But  There are some disadvantages Poor Biocompatibility Poor Water Solubility 5 Kriegel, I.; Fernandez, J. R.; Wisnet, A.; Zhang, H.; Waurisch, C.; Eychmuller, A.; Dubavik, A.; Govorov, A.O.; Feldmann, J., ACSNANO. 2013, 7,

Objectives  Develop a simple and environmentally friendly method to synthesize glutathione (GSH) capped CdSe QDs under mild chemical conditions.  Optimize the synthesis conditions to obtain CdSe QDs within a reasonable time period. 6

Imaginary structure of the capped CdSe QD 7 Kriegel, I.; Fernandez, J. R.; Wisnet, A.; Zhang, H.; Waurisch, C.; Eychmuller, A.; Dubavik, A.; Govorov, A.O.; Feldmann, J., ACSNANO. 2013, 7,

Method, Results and Discussion 1.Development of a method to synthesize GSH capped CdSe QDs 2.Optimization of the synthesis conditions to obtain CdSe QDs within a reasonable time period 8

9 1. CdCl 2 2. Borax-citrate buffer 3. Glutathione Method development for synthesis of GSH capped CdSe QDs CdSe QDs Pérez-Donoso, J. M.; Monrás, J. P.; Bravo, D.; Aguirre, A.; Quest, A. F.; Osorio-Román, I. O.; Aroca, R. F.; Chasteen, T. G.; Vásquez, C. C., PloS ONE 2012, 7(1), e Na 2 SeO 3 Keep on water bath 90°C

10 CdSe QDs at 90°C Synthetic mixture – after 2 h under room light Synthetic mixture - after 2 h under trans-illuminator QDs - after 2 h (resuspended in buffer) under trans-illuminator

11 1. CdCl 2 2. Borax-citrate buffer 3. Glutathione Optimization of the synthesis conditions CdSe QDs Pérez-Donoso, J. M.; Monrás, J. P.; Bravo, D.; Aguirre, A.; Quest, A. F.; Osorio-Román, I. O.; Aroca, R. F.; Chasteen, T. G.; Vásquez, C. C., PloS ONE 2012, 7(1), e Na 2 SeO 3 Keep on water bath at different temperatures 30°C, 40°C, 50°C, 60°C and 70°C

1. Temperature and growth time 12 Color variations of CdSe QDs - under trans-illuminator 1 h 3 h5 h7h24 h 48 h 144 h 1 h 3 h 5 h 7 h24 h 48 h 144 h 1 h 3 h 5 h 7 h 24 h 48 h 144 h 30°C 40°C 50°C

13 24 h 48 h 96 h 1 h3 h 5 h7 h 24 h 1 h 3 h5 h 7 h 60°C 70°C Color variations of CdSe QDs - under trans-illuminator

Temperature / o CColor variation range 30 Blue Green 40 Blue Yellow 50 Blue Orange 60 Green Yellow 70 Green Yellow 14 1 h 3 h 5 h 7 h 24 h 48 h 144 h 50°C Temperature and growth time - summary

2. Different reactant concentrations CdCl 2 : Na 2 SeO 3 4:1 CdCl 2 : Na 2 SeO 3 4: h 3 h 5 h 7 h 24 h 48 h 144 h 1 h 3 h 5 h 7 h 24 h 48 h72 h 1 h 3 h 5 h 7 h 24 h 48 h 72 h 1 h 3 h 5 h 7 h 24 h 48 h72 h CdCl 2 : Na 2 SeO 3 4:3 CdCl 2 : Na 2 SeO 3 4:4

Conclusions  CdSe QDs were successfully synthesized under mild chemical conditions.  The spectral behaviors of QDs depend on temperature and growth time.  The most suitable temperature for synthesis of CdSe QDs is 50 0 C with color varying from blue to orange color.  Larger size QDs (orange color) can be obtained in a reasonable time period by changing the reactant concentrations. 16

Acknowledgements  Supervisor- Dr. Thomas Chasteen, Department of Chemistry  Former members of Dr Chasteen’s Research group Mr. Tharaka Wansapura, Ms. Desire Lopez  Dr. José Manuel Pérez Donoso, Universidad de Santiago de Chile, Santiago, Chile.  Robert A. Welch foundation 17

18 Thank you