Sol-gel Synthesis

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Sol-gel Synthesis Characterization of
Luminescent Quantum Dots

• Laura Ingalls Huntley
• Prof. Christie LaRochelle
• PHY490 Senior Independent Study
• 04 May 2007

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Quantum Dots

• Semiconductor crystals of less than 10 nm in
  size. I.e. nanocrystals.
• Of particular interest due to their many
  applications in the fields of optoelectronics and
  quantum computing.
• Synthesis Sol-gel process to produce silica
  glasses doped with SnO2 and Tb3.
• Characterization optical spectroscopy, XRD, and
  TEM.

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Sol-gel Synthetic Method

• TEOS is hydrolyzed with water, ethanol, and acid.
• SnCl2 is dissolved in ethanol and added with
  stirring.
• Tb nitrate is dissolved and added after .5 hrs.
• Water/Ethanol/Acid mixture is added to complete
  hydrolyzation.
• Solution is transferred into plastic test tubes.

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Synthetic Method Cont.

• Solution in test tubes gels within 3-5 days as
  ethanol evaporates and crystals start to form.
• After gel is formed, pellet is removed from test
  tube and placed in 90 C oven for a period of
  approximately 2 days. Pellets will form small
  glasses.
• Glasses are then fired in tube furnace
  temperature is ramped from 90 C to 450 C in 9
  hours, then to 650 C in 20 minutes, and finally
  to 800 C in 5 hours. This temperature is
  maintained for 2 hours subsequently, the glasses
  are allowed to cool to room temperature.

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Optical Spectroscopy
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Optical Spectroscopy, Cont.
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XRD TEM

• XRD analysis showed only the SiO2 network. A
  higher concentration of tin may be needed for the
  SnO2 crystals to register on the XRD.
• TEM is the next step in characterizing the
  glasses. The TEM machine needs an extremely thin
  sample in order to work, this may be achieved by
  grinding the glasses into a powder, adding a
  resin, and then shaving off a small layer.
• However, the synthetic method could also be
  altered such that the glasses formed as a thin
  film.