Sol-gel Synthesis & Sol-gel Synthesis & Characterization of Luminescent Characterization of Luminescent

Quantum DotsQuantum Dots

Laura Ingalls HuntleyLaura Ingalls HuntleyProf. Christie LaRochelleProf. Christie LaRochelle

PHY490: Senior Independent StudyPHY490: Senior Independent Study04 May 200704 May 2007

Quantum Dots …Quantum Dots …

Semiconductor crystals of less than 10 nm in Semiconductor crystals of less than 10 nm in size. I.e. “nanocrystals.” size. I.e. “nanocrystals.”

Of particular interest due to their many Of particular interest due to their many applications in the fields of optoelectronics and applications in the fields of optoelectronics and quantum computing.quantum computing.

Synthesis: Sol-gel process to produce silica Synthesis: Sol-gel process to produce silica glasses doped with SnOglasses doped with SnO22 and Tb and Tb3+3+. .

Characterization: optical spectroscopy, XRD, Characterization: optical spectroscopy, XRD, and TEM.and TEM.

Sol-gel Synthetic MethodSol-gel Synthetic Method TEOS is hydrolyzed TEOS is hydrolyzed

with water, ethanol, with water, ethanol, and acid.and acid.

SnClSnCl22 is dissolved in is dissolved in ethanol and added ethanol and added with stirring.with stirring.

Tb nitrate is dissolved Tb nitrate is dissolved and added after .5 hrs.and added after .5 hrs.

Water/Ethanol/Acid Water/Ethanol/Acid mixture is added to mixture is added to complete complete hydrolyzation.hydrolyzation.

Solution is transferred Solution is transferred into plastic test tubes.into plastic test tubes.

Synthetic Method Cont.Synthetic Method Cont. Solution in test tubes gels within 3-5 days as ethanol Solution in test tubes gels within 3-5 days as ethanol

evaporates and crystals start to form.evaporates and crystals start to form.

After gel is formed, pellet is removed from test tube After gel is formed, pellet is removed from test tube and placed in ~ 90 and placed in ~ 90 °C oven for a period of °C oven for a period of approximately 2 days. Pellets will form small approximately 2 days. Pellets will form small glasses.glasses.

Glasses are then fired in tube furnace: temperature Glasses are then fired in tube furnace: temperature is ramped from 90 is ramped from 90 °C to 450°C to 450 °C in 9 hours, then to °C in 9 hours, then to 650650 °C in 20 minutes, and finally to °C in 20 minutes, and finally to 800 800 °C in 5 °C in 5 hours. This temperature is maintained for 2 hours; hours. This temperature is maintained for 2 hours; subsequently, the glasses are allowed to cool to subsequently, the glasses are allowed to cool to room temperature.room temperature.

Optical SpectroscopyOptical Spectroscopy

Emission Spectra, Excitation Wavelength = 266 nm

470 475 480 485 490 495 500 505 510 515 520

Emission Wavelength (nm)

Inte

ns

ity

Optical Spectroscopy, Cont.Optical Spectroscopy, Cont.

Emission Spectra, Excitation Wavelength = 266 nm

520 540 560 580 600 620 640 660

Emission Wavelength (nm)

Inte

ns

ity

XRD & TEMXRD & TEM XRD analysis showed only the SiOXRD analysis showed only the SiO22 network. A network. A

higher concentration of tin may be needed for higher concentration of tin may be needed for the SnOthe SnO2 2 crystals to register on the XRD.crystals to register on the XRD.

TEM is the next step in characterizing the TEM is the next step in characterizing the glasses. The TEM machine needs an extremely glasses. The TEM machine needs an extremely thin sample in order to work, this may be thin sample in order to work, this may be achieved by grinding the glasses into a powder, achieved by grinding the glasses into a powder, adding a resin, and then shaving off a small adding a resin, and then shaving off a small layer. layer.

However, the synthetic method could also be However, the synthetic method could also be altered such that the glasses formed as a thin altered such that the glasses formed as a thin film. film.