Synthesis of CdTe quantum dots and study of their stability.

Wansapura, P.T.; Chasteen, T.G.

• Introduction

• Materials and Methods

• Results and Discussion

• Conclusions

Introduction

• Quantum dots (QDs) are tiny particles, or “nanoparticles” (NPs).

• They were discovered at the beginning of the 1980s by Alexei Ekimov and Louis E. Brus.

• Traditionally chalcogenides (selenides, tellurides , sulfides) of metals like Cadmium or Zinc (CdSe or ZnS, for example).

• Range from 2 to 10 nanometers in diameter.

• Because of their small size, quantum dots display unique optical and electrical properties that are different in character from those of the corresponding bulk material.

• Emission photons under excitation, is visible to the human eye as light.

• The wavelength of these photon emissions depends on the its size.

• The ability to precisely control the size of a quantum dot enables the manufacturer to determine the wavelength of the emission, which in turn determines the colour of light the human eye perceives.

• Quantum dots can therefore be “tuned” during production to emit any colour of light desired.

• The smaller the dot, the closer it is to the blue end of the spectrum, and the larger the dot, the closer to the red end.

• Dots can even be tuned beyond visible light, into the infra-red or into the ultra-violet.

quarknet.fnal.gov (10.02.13)

• QDs exhibit important advantages such as

i) Narrow emission spectra,

ii) Increased chemical stability, iii) Tunable spectroscopic properties, iv) High quantum yields.

• At the end of the production process, quantum dots appear physically either as a powder or in a solution.

• Photovoltaic devices: solar cells• Biology : biosensors, imaging• Light emitting diodes: LEDs• Flat-panel displays• Memory elements• Photodetectors• Lasers

european-coatings.com (10.02.13)

openi.nlm.nih.gov (10.02.13)

blog.light-innovations.com (10.02.13)

CdTe-GSH (Glutathione) Quantum Dots

• The idea of slightly changing the shape of these QDs and hence their optical properties has made them very popular in optoelectronics.

• CdTe QDs are used in electronic and optoelectronic devices during the last decade, as an important tool for new solar cell technology (photovoltaic panels) and biomedicine.

Materials and Methods

• A CdCl2 (4 mM) solution was prepared in 15 mM borax-citrate buffer, (pH 9.0)

• Then glutathione (GSH) was added (up to 10 mM final).

• After 5 min, potassium tellurite ( K2TeO3) was added at 1 mM (final concentration) to produce a 4:10:1 ratio of CdCl2: GSH: K2TeO3.

• At this point the solution turned slightly green as result of CdTe ‘‘seeds’’ formation.

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.

• QDs nucleation was initiated by raising the temperature up to 900C.

• CdTe QD samples were obtained in every hour time intervals.

• CdTe-GSH QDs were precipitated with two volumes of ethanol and centrifuged for 20 min at 12,000 rpm.

• Fluorescence spectroscopic data obtained before and after the precipitation.

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.

• Dried QDs, QDs in buffer, and QDs in water were stored in under a variety of conditions involving different light intensities and temperatures.( 2hrs incubated QDs )

• 40C (under dark and light conditions), • -800C (under dark conditions), • Under sunlight, • Under room temperature conditions (under dark and light), • Under 1200 lumens bulb (fluorescent bulb),in replicate samples.

• Fluorescence spectrometric data were collected and analyzed periodically for three months.

Room Temp: In the

Lab

Room Temp: Under

Sunlight

Room Temp:Under 1200

Lumens Bulb

40C Under dark

40C Under Light / dark

-800CUnder dark

Room Temp: Underdark

QDs dissolved in Buffer

LB SB BB 4dB 4LB -80dB LdB

QDs dissolved

in deionized

water

LW SW BW 4dW 4LW -80dW LdW

QDs powder LN SN BN 4dN 4LN -80dN LdN

Results and Discussion

Freshly prepared QDs

After the resuspension of QDs, in the Buffer

1h 2h 3h 4h 5h 6h

1h 2h 3h 4h 5h 6h

Images under room light

0h 1h 2h 3h 4h 5h 6h

Freshly prepared QDs

Precipitated QDs

Dried QDs

Images of QDs in TransilluminatorA

B

CD

After the resuspension of QDs, in the Buffer

2hrs-Dried QDs under room light

2hrs-Dried QDs on transilluminator (302nm)

LB- Lab, RT, Light / SB- Sunlight / BB- Bulb / 4dB- 40C,dark / 4LB- 40C,Light / -80dB- -800C,Dark / LdB- Lab, RT, Dark

QDs in buffer

LB SB BB 4dB 4LB -80dB LdB LB SB BB 4dB 4LB -80dB LdB

0th day

18th day

24th day

32nd day

39th day

46th day

76th day

10th day

unde

r roo

m li

ght

On transillum

inator (302nm)

LW- Lab, RT,Light / SW- Sunlight / BW- Bulb / 4dW- 40C,dark / 4LW- 40C,Light / -80dW- -800C,Dark / LdW- Lab, RT,Dark

QDs in water

LW SW BW 4dW 4LW -80dW LdW LW SW BW 4dW 4LW -80dW LdW

0th day

18th day

24th day

32nd day

39th day

46th day

76th day

10th day

unde

r roo

m li

ght

On transillum

inator (302nm)

LN- Lab, RT, Light / SN- Sunlight / BN- Bulb / 4dN- 40C,dark / 4LN- 40C,Light / -80dN- -800C,Dark / LdN- Lab, RT, Dark

Dried QDs in Water

LN SN BN 4dN 4LN -80dN LdN LN SN BN 4dN 4LN -80dN LdN

0th day

18th day

24th day

32nd day

39th day

46th day

76th day

10th day

unde

r roo

m li

ght O

n transilluminator (302nm

)

Conclusions

• CdTe-GSH QDs were successfully synthesized (solutions and powders).

• Spectroscopic data shows that both QDs (solutions and powders) have similar Fluorescence characteristics.

• Dried QDs were more stable.(research continued)

• Under sunlight QDs in water and buffer showed degradation.(research continued)

Future works……

• Further studies of Fluorescence and Absorbance spectroscopic data.

• Stability studies – under different temperatures , dark / light conditions.(research continued)

• Inductively coupled plasma atomic emission spectroscopic (ICP-AES),analysis to find out the ratio of Cd/Te in QDs after the degradation.

ACKNOWLEDGEMENTS

• Dr. Chasteen’s Research group at Sam Houston State University.

• All the academic staff at Sam Houston State University.

• Dr. José Manuel Pérez Donoso and Dr. Waldo A. Dıáz-Vásquez Microbiology and BioNanotechnology Research Group

Laboratory of Biochemistry Facultad de Ciencias Químicas y Farmacéuticas Universidad de Santiago de Chile, Santiago, Chile.

• Ms. Rachelle Smith and staff - Texas Research Institute for Environmental Studies (TRIES).

• Robert A. Welch foundation.

THANK YOU

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