Synthesis of fluorescent CdSe quantum dots under mild chemical conditions

H. N. Rathnaweera and T. G. ChasteenDepartment 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.

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• Solar cells• Biosensors• Light emitting diodes• Flat-panel displays• Photo detectors• Lasers

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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.

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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

5Kriegel, I.; Fernandez, J. R.; Wisnet, A.; Zhang, H.; Waurisch, C.; Eychmuller, A.; Dubavik, A.; Govorov, A.O.; Feldmann, J., ACSNANO. 2013, 7, 4367-4377.

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.

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Imaginary structure of the capped CdSe QD

7Kriegel, I.; Fernandez, J. R.; Wisnet, A.; Zhang, H.; Waurisch, C.; Eychmuller, A.; Dubavik, A.; Govorov, A.O.; Feldmann, J., ACSNANO. 2013, 7, 4367-4377.

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

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1. CdCl2 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), e30741.

4. Na2SeO3

Keep on water bath 90°C

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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

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1. CdCl2 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), e30741.

4. Na2SeO3

Keep on water bath at different temperatures

30°C, 40°C, 50°C, 60°C and 70°C

1. Temperature and growth time

12Color variations of CdSe QDs - under trans-illuminator

1 h 3 h 5 h 7h 24 h 48 h 144 h 1 h 3 h 5 h 7 h 24 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

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24 h 48 h 96 h1 h 3 h 5 h 7 h

24 h1 h 3 h 5 h 7 h

60°C

70°C

Color variations of CdSe QDs - under trans-illuminator

Temperature / oC Color variation range

30Blue Green

40Blue Yellow

50Blue Orange

60Green Yellow

70Green Yellow

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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

CdCl2: Na2SeO3 4:1 CdCl2: Na2SeO3 4:2

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1 h 3 h 5 h 7 h 24 h 48 h 144 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 h 72 h 1 h 3 h 5 h 7 h 24 h 48 h 72 h

CdCl2: Na2SeO3 4:3 CdCl2: Na2SeO3 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 500C 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.

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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

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Thank you