Sol-gel Synthesis & Characterization of Luminescent Quantum Dots Laura Ingalls Huntley Prof. Christie LaRochelle PHY490: Senior Independent Study 04 May 2007

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 SnO 2 and Tb 3+.  Characterization: optical spectroscopy, XRD, and TEM.

Sol-gel Synthetic Method  TEOS is hydrolyzed with water, ethanol, and acid.  SnCl 2 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.

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.

Optical Spectroscopy

Optical Spectroscopy, Cont.

XRD & TEM  XRD analysis showed only the SiO 2 network. A higher concentration of tin may be needed for the SnO 2 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.