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.
A CdCl 2 (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 ( K 2 TeO 3 ) was added at 1 mM (final concentration) to produce a 4:10:1 ratio of CdCl 2 : GSH: K 2 TeO 3. 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 90 0 C. 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 ) 4 0 C (under dark and light conditions), -80 0 C (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 4 0 C Under dark 4 0 C Under Light / dark -80 0 C Under dark Room Temp: Under dark QDs dissolved in Buffer LBSBBB4dB4LB-80dBLdB QDs dissolved in deionized water LWSWBW4dW4LW-80dWLdW QDs powder LNSNBN4dN4LN-80dNLdN
LB- Lab, RT, Light / SB- Sunlight / BB- Bulb / 4dB- 40C,dark / 4LB- 4 0 C,Light / -80dB- -80 0 C,Dark / LdB- Lab, RT, Dark QDs in buffer LB SB BB 4dB 4LB -80dB LdB 0 th day 18 th day 24 th day 32 nd day 39 th day 46 th day 76 th day 10 th day under room light On transilluminator (302nm)
LW- Lab, RT,Light / SW- Sunlight / BW- Bulb / 4dW- 4 0 C,dark / 4LW- 4 0 C,Light / -80dW- -80 0 C,Dark / LdW- Lab, RT,Dark QDs in water LW SW BW 4dW 4LW -80dW LdW 0 th day 18 th day 24 th day 32 nd day 39 th day 46 th day 76 th day 10 th day under room light On transilluminator (302nm)
LN- Lab, RT, Light / SN- Sunlight / BN- Bulb / 4dN- 40C,dark / 4LN- 4 0 C,Light / -80dN- -80 0 C,Dark / LdN- Lab, RT, Dark Dried QDs in Water LN SN BN 4dN 4LN -80dN LdN 0 th day 18 th day 24 th day 32 nd day 39 th day 46 th day 76 th day 10 th day under room light On transilluminator (302nm)
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. Chasteens 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.